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Firefighting Foam - T~chnical

Volume 1Fire Service Technology,Equipment and Media

HM Fire Service Inspectorate Publications Section

London: The Stationery Office

Fire Service Manual

Issued under the authority of the Home Office(Fire and Emergency Planning Directorate)

The Fire ServiceCollege

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(01608) 650831 Ext.2338library@fireservicecollege.ac.uk

THE FIRE SERVICE COLLEGE LIBRARYMORETON-IN MARSHGLOUCESTERSHIRE

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© Crown Copyright 2000Published with the permission of the Home Officeon behalf of the Controller of Her Majesty's Stationery Office

Applications for reproduction should be made inwriting to The Copyright Unit, Her Majesty's Stationery Office,St. Clements House, 2-16 Colegate, NorwiCh, NR3 IBQ

FirefightingTechnical

Preface

oam-

ISBNO 11 341188 X

Cover photograph: The Fire Experimentation Unit

Half-title page photograph: West Midlands Fire Brigade

Printed in the United Kingdom for The Stationery OfficeTJ763 4/00 C50 5673

This manual, Volume 1, Fire Service Technology,Equipment and Media - Firefighting Foam, dealswith technical aspects of foam concentrates, stan­dards and equipment.

This book complements the eXisting manual inVolume 2 - Fire Service Operations - FirefightingFoam.

These books replace:

The Manual of Firemanship Book 3, Part 3

Dear Chief Fire Officer Letter 2/97 - FoamApplication Rates.

The Home Office is endebted to all those who havehelped in the preparation of this work, in particular:

Mr Bryan Johnson BSc.;Home Office Fire Experimental Unit;Mid and West Wales Fire Brigade;Angus Fire Armour Ltd;Williams Fire and Hazard Control Inc.;Civil Aviation Authority;British Fire Protection Association Ltd;Cheshire Fire Brigade;London Fire Brigade;Fire Service College;Dr Tony Cash;Northern Ireland Fire Brigade.

Home Office, April 2000

Firejighfing Foam - Technical111 [

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Firefighting Foam ­Technical

Contents

Preface Hi

Chapter 1 Introduction 1

1.1 General 11.2 Historical Development of Firefighting Foams 213 How Foams Extinguish Fires 31.4 Production of Finished Foam 31.4.1 General 31.4.2 Percentage Concentration 31.43 Aspiration 41.5 Foam Expansion Ratios 51.5.1 General 51.5.2 Equipment Used For Generating Different Expansion Ratio Foams 51.53 Foam Concentrates 51.5.4 Typical Uses and Properties of Low, Medium and High Expansion Finished Foams 6

Chapter 2 Foam Concentrate' 72.1 Types of Foam Concentrate 72.1.1 General 72.1.2 Protein Based Foam Concentrates 8

(a) Protein (P) 8(b) Fluoroprotein (FP) 9(c) Film-forming Fluoroprotein (FFFP) 9

2.13 Synthetic Based Foam Concentrates 9(a) Synthetic Detergent (SYNDET) 9(b) Aqueous Film-forming Foam (AFFF) 9

2.1.4 Alcohol Resistant Foam Concentrates (AFFF-AR and FFFP-AR) 102.1.5 Hazmat Foam Concentrates 112.1.6 Wetting Agents 112.1.7 Class A Foam Concentrates 122.1.8 Fuel Emulsifiers 122.2 Handling and Storage of Foam Concentrates 122.2.1 Compatibility 122.2.2 Viscosity 132.2.3 Corrosion 142.2.4 Storage and Use Temperature Conditions 142.2.5 Order of Use 152.2.6 Storage Containers and Bulk Storage 15

Firefighting Foam - Technical V Ir

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Chapter 4 The Propertie of Finished Foams and The Effectof These on irefighting Performance

Chapter 3 Foam Concentrate tandards and Periodic Testing3.1 General3.2 Physical Property Tests of Foam Concentrates3.2.1 General3.2.2 Specific Gravity (Relative Density)3.2.3 pH (acidity/alkalinity)3.2.4 Sediment (Sludge)3.2.5 Spreading Coefficient3.2.6 Effects of Freeze/Thaw3.2.7 Accelerated Ageing3.2.8 Viscosity3.3 Foam Concentrate Standard Fire Tests3.3.1 General3.3.2 Is the Fuel Commonly Encountered Operationally?3.3.3 Is the Fuel Reproducible?3.3.4 How Long is the Preburn?3.3.5 How Deep is the Fuel?3.3.6 What is the Application Rate?3.3.7 How is the Foam Applied?3.3.8 Under What Conditions are the Fire Tests Performed?3.3.9 What Burnback Test is Used?3.3.10 When are the Fire Tests Carried Out?3.4 Periodic Testing of Foam Concentrates3.4.1 General3.4.2 Collection of Foam Concentrate Samples3.4.3 Typical Physical Property Tests

(a) Specific Gravity (Relative Density)(b) pH (Acidity/Alkalinity)(c) Sediment (Sludge)(d) Spreading Coefficient

3.4.4 Periodic Fire Tests

Chapter 5 Equipment5.1 General5.2 Foam-Making Equipment5.2.1 General5.2.2 LX Hand-held Foam-making Branches

(a) How They Work(b) LX Foam-making Branch Performance

5.2.3 LX Hand-held Hosereel Foam Unit5.2.4 LX Foam Generators5.2.5 LX Foam Monitors5.2.6 MX Hand-held Foam-making Branches5.2.7 LX and MX Hand-held Water Branch 'Snap-on' Attachments5.2.8 MX Foam Pourers5.2.9 HX Foam Generators5.3 Foam Concentrate Induction and Injection Equipment5.3.1 General5.3.2 In-line inductors5.3.3 Round-the-pump Proportioners5.3.4 Pressure Control Valves5.3.5 Pressurised Foam Supply

(a) General(b) Distribution Manifold(c) Metering Devices(d) Inline Foam Injection (Pelton Wheel)(e) Pre-induction Units(f) Direct Coupled Water Pump

5.3.6 Hosereel Foam Induction and Injection Systems(a) General(b) Premix(c) Round-the-pump(d) Injection in to Pump Inlet(e) In-line Inductors(f) Suggestions for an Operational Requirement for a Hosereel Induction System

5.4 Compressed Air Foam Systems (CAFS)5.5 Methods For Checking Foam Solution Concentration as Produced by Foam-making

Equipment

4.14.24.34.44.54.64.74.84.94.104.114.124.134.13.14.13.2

GeneralWorkingFoam FlowlFluidityFilm FormationFuel ToleranceEdge SealingFoam Blanket StabilitylDrainage TimeVapour SuppressionBurnback ResistanceWater-miscible Fuel CompatibilitySuitability For Subsurface (Base) InjectionQuality of Finished FoamCompatibility of Finished FoamsWith Other Finished FoamsWith Dry Powder

17

171919191919192020202020202121212121222222222223242424242424

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272728282930303131323232333333

4.144.14.14.14.2

4.154.15.14.15.24.15.3

Typical Characteristics of Finished FoamsGeneralIndividual Foam Characteristics(a) P(b) FP(c) FFFP(d) Synthetic (SYNDET)(e) AFFF(f) Alcohol Resistant Foam Concentrates (AFFF-AR and FFFP-AR)Environmental Impact of Firefighting FoamsGeneralToxicityBiodegradability

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65

VI Fire Service Manual Firefighting Foam - Technical VU

5.5.15.5.25.5.3

GeneralRefractometer MethodFlow Method

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Firefighting Foam ­Technical

Chapter 6 Categorie of Fire and the se of Firefighting Foamgainst Them

6.1 Classes of Fire6.1.1 Class A fires6.1.2 Class B Fires

(a) General(b) High Flash Point Water-immiscible Class B Liquids(c) Low Flash Point Water-immiscible Class B Liquids(d) Water-miscible Class B Liquids

6.1.3 Class C Fires6.1.4 Class 0 Fires6.2 Electrical Fires6.3 Types of Liquid Fuel Fire6.3.1 General6.3.2 Spill Fires6.3.3 Pool Fires6.3.4 Spreading Fires6.3.5 Running Fires6.3.6 Other Terms

Chapter 7 Application Rates7.1 General7.2 Critical Application Rate7.3 Recommended Minimum Application Rate7.3.1 General7.3.2 Fires Involving Water-immiscible Class B Liquids7.3.3 Fires Involving Water-miscible Class B Liquids7.4 Optimum Application Rate7.5 Overkill Rate7.6 Continued Application Rate

References

Further Reading

Glossary of Term - Firefighting Foams

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VU 1 Fire Service Manual I------------

Firefighting Foam ­Technical

Chapter

Chapter 1 - Introduction

1.1 General

Firefighting foams have been developed primarilyto deal with the hazards posed by liquid fuelfires.

extracting the water they contain. This rapidlyleads to the complete destructjon of the foamblanket. Consequently, special firefighting foams,generally known as 'alcohol resistant' foam con­centrates, have been developed to deal with theseparticular types of liquid.

The main properties of firefighting foams include:

Some firefighting foams have also been developedspecifically for use against class A fires.

• Knockdown and extinction: the ability ofthe finished foam to control and extinguishfires.

• Expansion: the amount of finished foamproduced from a foam solution when it ispassed through foam-making equipment.

Burn-back resistance: the ability of the fin­ished foam, once formed on the fuel, to stayintact when subjected to heat and/or flame.

• Stability: the ability of the finished foam toretain its liquid content and to maintain thenumber, size and shape of its bubbles. Inother words, its ability to remain intact.

• Sealing and resealing: the ability of thefoam blanket to reseal should breaks occurand its abi Iity to seal against hot and irregu­lar shaped objects.

• Fluidity: the ability of the finished foam tobe projected on to, and to flow across, theliquid to be extinguished and/or protected.

• Contamination resistance: the ability of thefinished foam to resist contamination by theliquid to which it is applied.

•

Water is used for most firefighting incidents.However, it is generally ineffective against firesinvolving flammable liquids. This is because waterhas a density that is greater than most flammableliquids so, when applied, it quickly sinks belowtheir sUIfaces, often without having any significanteffect on the fire. However, when some burningliquids, such as heavy fuel oils and crude oils,become extremely hot, any water that is appliedwill begin to boil. The resulting rapid expansion asthe water converts to steam may cause burningfuel to ovelflow its containment and the fire tospread - this event is known as a slop-over. Also,the water that sinks below the fuel will collect inthe container and, should the container becomefull, this will result in the fuel overflowing.

Finished firefighting foams, on the other hand,consist of bubbles that are produced from a com­bination of a solution of firefighting foam concen­trate and water that has then been mixed with air.These air filled bubbles form a blanket that floatson the surface of flammable liquids. In so doing,the foam suffocates the fire and can lead to theknockdown and extinction of the flames.

The Jow density of firefighting foam blankets alsomakes them useful for suppressing the release ofvapour from flammable and other liquids. Specialfoam concentrates are available which allowvapour suppression of many toxic chemicals.

Water-miscible liquids, such as some polar sol­vents, can pose additional problems for firefight­ers. These quickly attack finished foams by

Firejighling Foam - Technical

The performance of firefighting foams can begreatly influenced by:

• The type of foam-making equipmentused and the way it is operated and maIn­tained.

• The type of foam concentrate used.

• The type of fire and the fuel involved.

• The tactics of foam application.

• The rate at which the foam is applied.

• The quality of the water used.

• The length of pre-burn.

The most effective and efficient use of firefightingfoam can only be achieved after full considerationhas been given to all of the above factors.

This Volume of the Manual describes a11 aspects offirefighting foam and discusses the types of equip­ment typically used by the fire service to produceit. Topics covered include the properties of foamconcentrates, finished foams and foam equipment;application rates; and the classes of, and types of,fire for which foam can be used.

Volume 2 of the Manual describes the operationaluse of foam including recommended minimumapplication rates and application techniques;practical scenario considerations; and the logis­tics involved in dealing with fires in storagetanks.

At the rear of this Volume, there is a glossary ofterms used in this Manual and other terms thatmay be used in connection with firefightingfoams.

It must be stressed that this Manual only givesgeneral information on the use of firefightingfoams. Incidents requiring the use of foam arevaried and preplanning in support of an effec­tive risk assessment at the commencement of anincident is of the utmost importance to ensurethat the correct foams, equipment and tacticsare selected and employed.

1.2 Historical Development ofFirefighting Foams

1877 - Chemical foam, first patented by a Britishscientist.

1904 - First successful use of chemical foam.Used to extinguish an I I metre diameter naphthastorage tank fire in Russia. Foam produced frommixing together large quantities of two chemicalsolutions.

1914 - Austrian engineers produce foam byintroducing a powder into running water.

1920s - Protein foam concentrate first producedalong with equipment designed for the productionand delivery of this first 'mechanical' foam.

1930s - Development of early chemical foamswith alcohol resisting properties. The concepts ofaspiration and proportioning were developed formechanical foam systems much as we know themtoday. Experimental work started on synthetictypes of foam concentrate.

1940s - 3% Protein foam concentrates developedto offer space and weight savings over the exist­ing 6% concentrates.

1950s - Low, medium and high expansion foamscould now be produced from a single syntheticfoam concentrate. First water-miscible liquidresistant mechanical foam concentrate developed.

1960s - Fluoroprotein and AFFF (Aqueous Film­forming Foam) foam concentrates developed.Improved alcohol resistant foams developed.

1970s - Further development of alcohol resistantfoam concentrates to produce mUlti-purpose foamsfor use at 3% on hydrocarbons and 6% on water­miscible liquids. "Hazmat" foams developed for thesuppression of vapour from hazardous materials.

1980s - Development of alcohol resistant foamconcentrates to produce AFFF-AR (alcohol resis­tant AFFF). Development of fluoroprotein foamsto produce FFFP (Film-forming Fluoroprotein)and multi-purpose FFFP-AR (Alcohol ResistantFFFP) foam concentrates.

1990s - Development of alcohol resistant foamconcentrates to produce versions that can be usedat 3% concentration on both hydrocarbons andwater-miscible liquids. Introduction of class Afoam concentrates.

1.3 How Foams Extinguish Fire

Firefighting foam is much lighter (less dense) thanall liquid fuels and so it floats on their surfaces.The foam blankets that are formed help to knock­down and extinguish these fires in the followingways:

• By excluding air (oxygen) from the fuelsurface.

• By separating the flames from the fuelsurface.

• By restricting the release of flammablevapour from the surface of the fuel.

• By forming a radiant heat barrier whichcan help to reduce heat feedback fromflames to the fuel and hence reduce theproduction of flammable vapour.

• By cooling the fuel surface and any metalsuli'aces as the foam sol ution drains outof the foam blanket. This process alsoproduces steam which dilutes the oxygenaround the fire.

1.4 Production of Fini bed Foam

1.4.1 General

Finished foam is produced from three main ingre­dients; foam concentrate, water and air. There areusually two stages in its production. The firststage is to mix foam concentrate with water toproduce a foam solution. The foam concentratemust be mixed into the water in the correct pro­portions (usually expressed as a percentage) inorder to ensure optimum foam production andfirefighting performance. This proportioning isnormally carried out by the use of inductors (orproportioners) or other similar equipment. Thisresults in the production of a 'premix' foam solu­tion. In other words, the foam concentrate and

water have been mixed together prior to arrivingat the foam-making equipment. Occasionally,premix solutions are produced by mixing the cor­rect proportions of water and foam concentrate ina container, such as an appliance tank, prior topumping to the foam-making equipment. In addi­tion, some types of foam-making equipment arefitted with a means of picking up foam concen­trate at the equipment; these are known as 'self­inducing' with the mixing taking place in thefoam-making equipment itself.

The second stage is the addition of air to the foamsolution to make bubbles (aspiration) to producethe finished foam. The amount of air addeddepends on the type of equipment used. Hand-heldfoam-making branches generally only mix rela­tively small amounts of air into the foam solution.Consequently, these produce finished foam withlow expansion (LX) ratios, that is to say, the ratioof the volume of the finished foam produced bythe nozzle, to the volume of the foam solution usedto produce it, is 20: 1 or less. Other equipment isavailable which can produce medium expansionfoam (MX) with expansion ratios of more than20: I but less than 200: 1, and high expansion foam(HX) with expansion ratios of more than 200: I andpossibly in excess of 1000: 1.

The following Sections describe in more detailsome of the important factors of foam productionthat were introduced above.

1.4.2 Percentage Concentration

All foams are usually supplied as liquid concen­trates. These must be mixed with water, to form afoam solution, before they can be applied to fires.They are generally supplied by manufacturers aseither 6%, 3% or I % foam concentrates. Thesehave been designed to be mixed with water as fol­lows:

• 6% concentrates6 parts foam concentrate in 94 parts water,

• 3 % concentrates3 parts foam concentrate in 97 parts water,

• 1% concentratesI palt foam concentrate in 99 parts water.

2 Fire Service Manual Firefighring Foam - Technical 3

It is also vely important to have compatibility offoam-making equipment and induction equipment,and just as importantly, foam induction equipmentmust be checked regularly to ensure that it is operat­ing correctly and giving an accurate rate of induction.

Once the correctly mixed foam solution has beendelivered to the end of a hose line, there are a num­ber of forms in which it can be applied to the fire.Generally, foam application is referred to as beingeither' aspirated' or 'non-aspirated':

1% concentrate is basically six times as strong as6% concentrate, and 3% concentrate is twice asstrong as 6% concentrate. However, the firefightingcharacteristics of finished foam produced from 1%.3% and 6% concentrates of a particular type ofmanufacturer's foam should be virtually identical.

The lower the percentage concentration, the lessfoam concentrate that is required to make fin­ished foam. The use of say 3% foam concentrateinstead of 6% foam concentrate can result in ahalving of the amount of storage space requiredfor the foam concentrate. with similar reductionsin weight and transportation costs, while main­taining the same firefighting capability. Not allfoam concentrates are available in the highly con­centrated J% form, e.g. alcohol resistant and pro­tein based foam concentrates. This is becausethere are technical limits to the maximum usageconcentrations of some of the constituents offoam concentrates.

For flammable liquid fuel fires, effective sec­ondary aspirated foam can only be produced usinga film-forming foam concentrate.

The amount that a foam solution can be aspiratednot only depends on the equipment, but also on thefoam concentrate that is used. For instance, syn­thetic detergent (SYNDET) foam concentrates arethe only type that can be used to produce low,medium and high expansion foams; protein foamconcentrates can only be used to produce lowexpansion foam and the remaining commonly usedfoam concentrates (i.e. AFFF, AFFF-AR, FP, FFFPand FFFP-AR. see Chapter 2) are mostly intendedfor use at low expansion. although they can also beused to produce medium expansion foam.

Chapters 2, 3 and 4 discuss in detail the varioustypes and properties of foam concentrates and fin­ished foams.

Medium and high expansion foams are usually pri­mary aspirated through special foam-makingequipment. This equipment produces foam byspraying the foam solution on to a mesh screen ornet. Air is then blown through the net or mesheither by entrainment caused by the spray nozzle,or by an hydraulic. electric or petrol motor drivenfan.

1.5.3 Foam Concentrates

Primary aspirated low expansion foams areusually produced by using purpose designed foam­making branches or mechanical generators.

1.5.2 Equipment Used For GeneratingDifferent Expansion Ratio Foams

Secondary aspirated low expansion foams are usu­ally produced by using standard water deliverydevices although some purpose designed largecapacity monitors have been produced for this par­ticular type of application (see Volume 2).

Secondary aspirated foams generally have anexpansion ratio of less than 4: I.

• Low expansion less than or equalto 20: I

• Medium expansion greater than 20: Ibut less than orequal to 200: I

• High expansion greater than 200: I

Typical firefighting foam expansion ratio rangesare:

1.5.1 General

Expansion ratio

This foam would also be referred to as having anexpansion of 8.

As mentioned previously, finished foam is usuallyclassified as being either low, medium or highexpansion. The expansion, or more strictly theexpansion ratio, of a foam is the ratio of the vol­ume of the finished foam to the volume of thefoam solution used to produce it. For example. if100 litres of foam solution were passed through afoam-making branch and 800 litres of foam wereproduced, then the expansion ratio of the foamwould be calculated as follows:

volume of foam volume of foam solution

8

800 litres 100 litres

It is highly unlikely that a foam solution can beapplied operationally to a fire in such a way that noaspiration occurs. However, should such circum­stances occur, then this would be referred to as anon-aspirated application. Some water additives,such as wetting agents, may be formulated so thatthey do not foam; use of these types of additivewould result in non-aspirated application, eventhrough purpose designed foam-making equipment.

can be advantageous if rapid film-formation on afuel is required (see Chapter 4, Section 4.4).

1.5 Foam Expansion Ratios

t

t

,

• As it travels through the air due to theturbulence produced by the stream.

• 'Aspirated' foam is made when the foamsolution is passed through purposedesigned foam-making equipment, such asa foam-making branch. These mix in air(aspirate) and then agitate the mixturesufficiently to produce uniformly sizedbubbles (finished foam).

• As. it leaves the branch.

• When it strikes an object. This causesfUI1her turbulence and air mixing.

• 'Non-aspirated' implies that no aspirationof the foam solution has taken place.

Consequently, the term 'non-aspirated foam' isoften used incorrectly to describe the product of afoam solution that has been passed through equip­ment that has not been specifica.lly designed toproduce foam, such as a water branch. However,the use of this type of equipment will often resultin some aspiration of a foam solution. This isbecause air is usually entrained into the jet or sprayof foam solution:

There is sufficient air entrained by these processesto produce a foam of very low expansion (oftenwith an expansion ratio of less than 4: I).

• Primary aspirated foam - finished foamthat is produced by purpose designed foam­making equipment.

To more accurately describe the different types offinished foam produced. the terms 'primary' or'secondary' aspirated are preferred:

• Secondary aspirated foam - finishedfoam that is produced by all other means,usually standard water devices.

Secondary aspiration will normally result in a poorquality foam being produced, due to insufficientagitation of the foam/air mixture. That is to say, thefoam will generally have a very low expansionratio and a very short drainage time (see below).However. foam blankets with short drainage times

Aspiration

It is extremely important that the foam inductionequipment used is set to the correct percentage. If3% concentrate is induced by an induction systemset for 6% concentrate, then twice the correctamount of foam concentrate will be used creatinga foam solution rich in foam concentrate. Not onlywill this result in the foam supply being depletedvery quickly and an expensive waste of foam con­centrate, but it will also lead to finished foam withless than optimum firefighting performance,mainly due to the foam being too stiff to flow ade­quately. Alternatively, using 3% foam concentratewhere the system is set for I% will result in a solu­tion with too little concentrate to make foam withadequate firefighting performance.

1.4.3

4 Fire Service Manual Firejighling Foam - Technical 5 [

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Chapter 2 - Foam Concentrates

1.5.4 Typical Uses and Properties of Low,Medium and High ExpansionFinished Foams

The various expansion ratios are typically used forthe following applications:

• Primary Aspirated Finished Foams

Medium expansion finished foam can only beprojected over small distances. However, withexpansions of between 20 and 200, large quantitiesof foam are produced from relatively smallquantities of foam solution. This, combined withits ability to flow relatively easily, makes mediumexpansion foam ideal for covering large areasquickly.

F-refghtingTechnical

oam- h pter

Low expansionLarge flammable liquid fires (i.e. storagetanks, tank bunds)Road traffic accidentsFlammable liquid spill firesVapour suppressionHelidecksJettiesAircraft crash rescuePortable fire extinguishers

Medium expansionVapour suppressionFlammable liquid storage tank bundsSmall cable ductsSmall fires involving flammable liquids,such as those following road trafficaccidentsTransformer protection

High expansionKnockdown and extinction in, andprotection of, large volumes such aswarehouses, aircraft hangars, cellars, sh ips'holds, mine shafts, etc.Large cable ductsVapour suppression (including cryogenicliquids such as LNG/LPG)

• Secondary Aspirated Finished Foams

Large flammable liquid fires (i.e. storage tanks,tank bunds)HelidecksAircraft crash rescuePortable fire extinguishers

Low expansion finished foams can be projectedover reasonably long distances and heightsmaking them suitable in many situations for useagainst fires in large storage tanks.

High expansion finished foam flows directly outof the foam-making equipment and is not project­ed any appreciable distance. Its coverage of largeareas can also be slow but the immense quantity offoam produced (expansion ratios are sometimes inexcess of 1000: I) can quickly fill large enclosures.Often, flexible ducting is required to transport thefoam to the fire. Due to its volume and lightness,high expansion foam is more likely than low andmedium expansion foam, to break up in moderate­ly strong wind conditions (Reference I).

The equipment used to produce secondary aspirat­ed foam is often standard water type branches andnozzles although there are some specificallydesigned large capacity nozzles available. Thefoam produced in this way is not well worked (seeChapter 4, Section 4.2), has a very low expansionratio and short drainage time, and tends to be veryfluid. These properties, combined with the film­forming nature of the foam concentrates used, canresult in a finished foam blanket that can quicklyknockdown and extinguish fires of some liquidhydrocarbon liquid fuels. This ability can makethem ideal for use in certain firefighting situationssuch as aircraft crash rescue. However, the foamblanket tends to collapse quickly, so providingvery poor security and resistance to burnback.

Secondary aspirated foam can be thrown over agreater distance than is possible with primary aspi­rated low expansion foam. This has resulted inequipment being designed specifically to projectsecondary aspirated foam into large storage tankfires. Manufacturers of this equipment recommendthe use of film-forming foam concemrate types forsuch applications. They claim that the finishedfoam produced usually has an expansion ratio ofless than 4: I .

2.1 Types of Foam Concentrate

2.1.1 General

There are a number of different types of foam con­centrate available. Each type normally falls intoone of the two main foam concentrate groups, thatis to say, they are either protein based or syntheticbased, depending on the chemicals used to pro­duce them.

• Protein based foam concentrates include:Protein (P)Fluoroprotein (FP)Film-forming f1uoroprotein (FFFP)Alcohol resistant FFFP (FFFP-AR)

• Synthetic based foam concentratesinclude:

Synthetic detergent (SYNDET)Aqueous film-forming foam (AFFF)Alcohol resistant AFFF (AFFF-AR)

The characteristics of each of these foam concen­trates, and the finished foams produced from them,varies. As a result, each of them has particularproperties that makes them suitable for someapplications and unsuitable for others.

For protein based foam concentrates, the basicchemical constituent is hydrolysed protein,obtained from natural animal or vegetable sources.It is the hydrolysed protein (the 'foaming agent')that enables bubbles to be produced.

For synthetic based foam concentrates, the basicconstituents are detergent based foaming agents.

To enhance the firefighting properties of thesebasic constituents, and hence produce the differentfoam concentrate types, chemicals are added.

Various types of surface active agents (or surfac­tants) are added to many firefighting foam concen­trates. These are used to reduce the amount of fuelpicked up by the finished foam on impact with fuel(i .e. they increase fuel tolerance) and to increasethe fluidity of the finished foam (i.e. they make iteasier for finished foam to flow over some fuelsand other surfaces).

Surface active agents are also used as foamingagents because they readily produce foam bubbleswhen mixed with water. Consequently, hydrocar­bon surface active agents, or as they are more com­monly known, synthetic detergents, are the mainconstituents of synthetic based foam concentrates.Surface active agents are also used in some proteinbased foams.

Surface active agents can help to reduce the sur­face tension of water. This not only helps in theformation of foam bubbles but also increases theability of the water to penetrate and spread. This isparticularly important when fighting class A firesbecau e it can help water to penetrate and cool theburning material.

In film-forming foam concentrates, surface activeagents form an aqueous film of foam solutionwhich, in certain conditions, can rapidly spreadover the surface of some burning hydrocarbons toaid knockdown and extinction.

Other chemicals may also be added to foamconcentrates. These include corrosion inhibitors,solvents (to reduce viscosity and to enhance foam­ing properties), preservatives (to prevent thegrowth of bacteria and moulds), stabilisers (to helpmaintain foam bubble stability) and anti-freezechemicals. These all help to prevent various prob­lems that could arise if only the basic chemicalconstituents of the foam concentrates were used.

-6 Fire Service Manual Firejighling Foam - Technical 7

In addition to the two main foam concentrategroups, other specialised foam concentrates andwater additives are available, in particular:

• Hazmat foam concentrates - for vapoursuppression of toxic, odorous and/orflammable materials.

• Wetting agents for increasing thepenetrating abil ities of water.

• Class A foam concentrates - primarily foruse on class A fires.

• Fuel emulsifiers - emulsion formingadditives for use primarily on class B firesfor firefighting and to prevent re-ignition.

Note that P, FP, FFFP, SYNDET and AFFF con­centrates are often referred to as .conventional'foam concentrates in order to distinguish themfrom alcohol resistant foam concentrates and thespecialised foam concentrates and water additivesmentioned above.

There are many companies manufacturing foamconcentrates and the quality of the products variesfrom manufacturer to manufacturer. In addition,the quality of a particular manufacturer's versionof a foam concentrate may vary slightly on a dailybasis due to acceptable variations in the base mate­rials used and other factors invol ved in the manu­facturing process. To complicate this even further,some manufacturers produce different grades ofthe same foam concentrate type for different mar­kets and, obviously, for use at different concentra­tions.

Consequently, the information contained withinthis Chapter gives an indication of the typical char­acteristics of each of the main types of foam con­centrate. Good quality foam concentrates mayhave better characteristics, those of poor qualityfoam concentrates may be considerably worse.These characteristics will, in any case, varydepending on the equipment and tactics used, thesize and type of incident and the fuel involved.

Some foam concentrate standards can help to dis­tinguish good from bad quality products for certainapplications. However, these standards need to beclosely scrutinised to ensure that they meet thewide range of fire service requirements (seeChapter 3).

This Chapter provides information on each of thedifferent types of foam concentrate and wateradditives mentioned above. Information is alsogiven on the storage and handling characteristicsof foam concentrates. However, the manufacturersshould always be consulted regarding the suitabil­ity of materials used for the storage and handlingof their products.

2.1.2 Protein Based FoamConcentrates

(a) Protein (P)

Protein foam concentrates are liquids that containhydrolysed protein with, typically, the addition ofstabilising additives and inhibitors to help preventcorrosion, resist bacterial decomposition, controlviscosity and improve their shelf life. Chemicaladditives can include salts of iron and calcium,sodium chloride and solvent.

The starting materials for production. which pro­vide the protein base product, include: soya beans,corn gluten, animal blood, horn and hoof meal,waste fish products and feather meal.

Protein foam concentrates are inexpensive and areusually manufactured for use at 3% or 6% concen­trations. Versions are available that can be mixedwith sea and fresh water. They are only intendedfor the production of low expansion finishedfoams.

In the past, protein foam concentrates have beenwidely used by industry, the fire service, the armedforces and aviation authorities throughout theworld. They have now been largely superseded byfluoroproteins and film-forming foam concen­trates although large stocks are still sometimesheld.

Often, protein foam concentrates do not containcorrosion inhibitors as the concentrate is not con­sidered to be particularly corrosive. However,incidents have indicated that some corrosion hastaken place in unprotected carbon steel bulk stor­age containers. Consequently, materials such asepoxy coated carbon steel, GRP (Glass ReinforcedPlastic) and polyethylene should be considered forthe storage of protein foam concentrate.

(b) Fluoroprotein (FP)

FP foam concentrates basically consist of proteinfoam concentrates with the addition of fluorinatedsurface active agents (fluorosurfactants). The addi­tion of fluorosurfactants provides oleophobic (oilrepellent) propelties and makes the finished foammore fluid. This greatly improves the fire knock­down performance of the finished foam whencompared to that of protein foam. Other additivescan include solvent, sodium chloride, iron, magne­sium and zinc.

FP foam concentrates are usually available for useat 3% or 6% concentrations and versions are avail­able for use with sea and fresh water. They areonly marginally more expensive than protein foamconcentrates.

FP foam concentrates are primarily intended forthe production of low expansion foams althoughthey have also proved effective when used to pro­duce medium expansion foam. They are not rec­ommended for the production of high expansionfoam.

Uses are widespread in the fire service, the petro­chemical industry and armed forces throughout theworld. As with protein foam concentrates, COITO­

sion inhibitors are not often included. However,consideration should be given to constructing bulkstorage containers from materials such as epoxycoated carbon steel, GRP or polyethylene.

(c) Film-forming Fluoroprotein (FFFP)

FFFP foam concentrates are based on FP foamconcentrates with the addition of film-forming flu­orinated surface active agents. Under certain con­ditions, this combination of chemicals can, as wellas producing a foam blanket, allow a very thinvapour sealing film of foam soLution to spreadover the sUli'ace of some liquid hydrocarbons.

FFFP foam concentrates are usually available foruse at 3% or 6% concentrations. They are primari­ly intended for the production of low expansionfoam although they can also be used to producemedium expansion foam. Also, due to their film­forming properties, they can be applied secondaryaspirated and can be used to tackle class A fires.

FFFP foam concentrates are not recommended forthe production of high expansion foam.

FFFP foam concentrates are more expensive thanP and FP foam concentrates.

As with P and FP foam concentrates, considerationshould be given to constructing bulk storage con­tainers from materials such as epoxy coated carbonsteel, GRP or polyethylene.

2.1.3 Synthetic 8ased FoamConcentrates

(a) Synthetic Detergent (SYNDET)

SYNDET foam concentrates were developed fromearly synthetic detergent foams and are based on amixture of anionic hydrocarbon surface activeagents, solvents and foam stabilisers.

SYNDET foam concentrates are versatile, as theycan be used to produce low, medium and highexpansion foams. They can also be used on class Aand class B fires. In the UK, their use is usuallylimited to medium and high expansion foams.However, in other European countries such asGermany and Sweden, SYNDET foam is used forlow expansion applications.

SYNDET foam concentrates are usually manufac­tured for use at between I% and 3% concentra­tions and versions are available for use with seaand fresh water. They are of similar cost to P andFP foam concentrates.

Manufacturers have indicated that SYNDET foamconcentrates are not particularJ y corrosi ve.However, testing (Reference 2) and reportsreceived from brigades indicate that adverse corro­sion and degradation effects can occur with mate­rials such as epoxy coated carbon steel, GRP andaluminium. Materials that should be consideredfor bulk storage containers and equipment for bothconcentrate and solution are 316 stainless steel orpolyethylene.

(b) Aqueous Film-forming Foam (AFFF)

AFFF foam concentrates are solutions of fluoro­carbon surface active agents and synthetic foaming

-8 Fire Sen'ice Manual Firejighting Foam - Technical 9

AFFF foam concentrates are of similar cost toFFFP foam concentrates.

AFFF is widely accepted for crash rescue fire­fighting uses and on less volatile fuels such askerosene and diesel oil. It is widely used offshoresecondary aspirated for helideck protection at aconcentration of 1%.

Hazmat Foam Concentrates

Wetting Agents

2.1.5

Hazmat foam concentrates have been designed tobe effective on products which destroy foams bychemically reacting with them. Versions of thesefoam concentrates are available that have been for­mulated to be resistant to either extreme acidity orextreme alkalinity. They are often used to producemedium expansion foams with optimum expan­sion ratios of around 60: I .

Some of the conventional firefighting foams dis­cussed above may be used for vapour suppressionon spills of flammable and combustible products.Also, a certain amount of success has beenachieved with them on toxic spills. However,many chemicals destroy firefighting foams eitherby reacting with them or by extracting the waterfrom foam blankets. Alcohol resistant foams canbe effective on some toxic spills and flammable,combustible and water-miscible liquids.

Firefighting Foam - Technical 11

Many materials used in industrial and chemicalprocesses release toxic, odorous and/or flammablevapour when in contact with the atmosphere. If aspill occurs, the hazard can be reduced by sup­pressing the released vapour until the spill can beneutral ised and disposed of.

Developments in this area include an additive foruse in conjunction with one particular alcoholresistant foam concentrate that significantly slowsdown the drainage rate of the finished foam to pro­duce a very stable foam blanket that lasts in excessof 12 hours. This can be used on hazardous mate­rials and is easily washed away with a water sprayafter use. However, additional equipment isrequired to mix the additive into the foam solutionline on application.

If there is doubt concerning the suitability of afoam concentrate for a particular task, the manu­facturer of the foam concentrate should be con­sulted to ensure that it can be used safely andsuccessfully.

2.1.6

Wetting agents are liquids which, when added towater in the required proportion, reduce thesurface tension of the water and increase its

Alcohol resistant foam concentrates are primarilydesigned for the production of low expansionfoams although they may also be used to producemedium expansion foams for application to hydro­carbon and water-miscible liquids. Versions areavailable for use with sea and fresh water.

The viscosity (see this Chapter, Section 2.2.2) ofalcohol resistant foam concentrates can vary enor­mously; some flow relatively easily while it can bedifficult to pour others out of their containers. Inaddition, they become more viscous with fallingtemperature. Consequently, if these foam concen­trates are to be used, it is important to ensure thatexisting induction equipment will pick them up atthe correct rate when using typical operationalequipment and conditions. For instance, whenusing the more viscous foam concentrates, it islikely that in-line inductor dial settings will beincorrect and not as much concentrate as indicatedwill be picked-up. As a result, when using theseviscous foam concentrates, foam induction sys­tems may need to be re-calibrated. In addition, asthe temperature of the alcohol resistant foam con­centrates falls towards freezing (O°C), the rate atwhich they are picked up by the induction systemwill reduce further, due to increasing viscosity,possibly even making the re-calibration inaccu­rate.

3%/6% concentrates are similar in price to stan­dard AFFF and FFFP concentrates whereas themanufacturers tend to charge more for the single3% concentrates.

For AFFF-AR, the suggested materials for bulkstorage containers and equipment are the same asAFFF, that is stainless steel, GRP, epoxy lined car­bon steel and polyethylene.

For FFFP-AR, as with P, FP and FFFP foam con­centrates, it is suggested that bulk storage contain­ers should ideally be constructed from materialssuch as epoxy coated carbon steel, GRP or poly­ethylene.

Alcohol resistant versions of P, FP and SYNDETfoam concentrates are available although they areuncommon in the UK. They are used in otherEuropean countries, in particular, FP-AR is widelyused in France.

AFFF-AR and FFFP-AR foam concentrates con­tain a polymeric additive which rapidly falls to thesurface of a water-miscible liquid when the fin­ished foam comes into contact with it. The poly­meric additive forms a tough 'skin' (also knownas a 'raft' or 'membrane') on the surface of theliquid. Once formed, the water-miscible liquidcannot penetrate this skin and is hence unable toattack the finished foam above it; conventionalfoams cannot form these water-miscible liquidresistant skins.

Non-alcohol resistant foam concentrates (i.e. P, FP,FFFP, SYNDET and AFFF) are not suitable for useon water-miscible liquids because their finishedfoam blankets quickly disintegrate on contact withthese liquids. This happens because the water con­tained in the foam rapidly mixes with, and isextracted by, the water-miscible liquids causingthe foam to quickly break down and disappear.

Two types of alcohol resistant foam concentrateare in general use in the UK fire service; thosebased on synthetic aqueous film-forming foams(AFFF-AR) and those based on film-forming fluo­roprotein foams (FFFP-AR). Alcohol resistantfoams can also usually be used on hydrocarbonfuels and because of this are sometimes known asmulti-purpose foams.

It should be noted that the polymeric membrane isnot formed when alcohol resistant foams areapplied to hydrocarbon fuels. It is also important tonote that although AFFF-AR and FFFP-AR fin­ished foams form aqueous films on some liquidhydrocarbon fuels, it is not possible for them, orany other foams, to form aqueous films on water­miscible liquids. They will, however, form anaqueous film between the polymeric membraneand the finished foam blanket. This may help toquicken the repair of any breaks that may occur inthe polymeric layer.

Alcohol resistant foam concentrates are normallyused at 6% concentration for application to firesof water-miscible fuels, such as most polar sol­vents, and at 3% concentration on liquid hydro­carbon fuel fires. However, some alcohol resistantfoam concentrates have been specificallydesigned for use at 3% concentration on bothwater-miscible and hydrocarbon fuels. The

Alcohol Resistant FoamConcentrates (AFFF·AR andFFFP-AR)

Fire Service Manual

AFFF foam concentrates are usually available foruse at 1%, 3% or 6% concentrations and versionsare available for use with fresh and sea water. Theyare primarily intended for the production of lowexpansion foams although they can also be used toproduce medium expansion foams. Due to theirfilm-forming properties. they can be applied sec­ondary aspirated and can be used to tackle class Afires. AFFF foam concentrates are not recommend­ed for the production of high expansion foam.

Problems have been experienced when attemptingto extinguish fires involving liquids with highvapour pressures, such as hexane and high octanepetrol, where quantities of vapour have penetratedthin, very low expansion (secondary aspirated)AFFF foam blankets.

agents. Under certain conditions, this combinationof chemicals can, as well as producing a foamblanket, allow a very thin vapour sealing film offoam solution to spread over the surface of someliquid hydrocarbons.

2.1.4

10

AFFF foam concentrate is not particularly corro­sive and contains no special corrosion inhibitors.However, its surface active agent content causesthe concentrate to be more searching than waterand therefore more corrosive. Materials thatshould be considered for materials for storage con­tainers and handling equipment are stainless steel,GRP, epoxy lined carbon steel and polyethylene.

Alcohol resistant foam concentrates have beendeveloped to deal with fires involving water-mis­cible liquids such as alcohols and some petrolblends containing high levels of alcohols and othersimilar fuel performance improvers.

•

Tests carried out in the UK (Reference 4) haveshown that class A foams. and the two convention­al foams tested (i.e. AFFF and SYNDET), perform

Some dedicated wetting agents are also recom­mended for use on class B fires. Some limited tests(Reference 3) have indicated that they are unsuit­able for this type of application.

concentrate through pick-up tubes, pipework andinduction equipment. Liquids are generally classedas either being non-Newtonian or Newtonian.

In addition, the viscosity of all foam concentrateswill vary with temperature and may be affected bythe age of the foam concentrate. Manufacturersoften state the viscosity of their products whenmeasured at 20DC; lower temperatures will resultin much higher viscosity.

Many alcohol resistant foam concentrates are con­sidered to be non-Newtonian pseudo-plastic liq­uids. For these liquids, as their flow increases,their viscosity decreases and so they flow moreeasily. Consequently, getting them to flow initiallycan be difficult, but once flowing, their viscosityreduces to a more acceptable level.

In contrast, the viscosity of Newtonian liquids,such as most non-alcohol resistant foam concen­trates, remains the same no matter how quickly orslowly they are flowing.

Firejighling Foam - Technical 13

Viscosity will also vary with foam concentratetype and with concentration. AFFF foam concen­trates at 3% and 6% concentrations tend to be theleast viscous, closely followed by P, FP and FFFPfoam concentrates at 6%. AFFF at I% and SYN­DET foams, P, FP and FFFP foam concentrates at3% concentration are appreciably more viscousthan these. The alcohol resistant foams are oftenthe most viscous although recent developmentshave dramatically reduced the viscosity of someproducts.

Manufacturers may also quote a 'Lowest UseTemperature' or 'Minimum Use Temperature' fortheir foam concentrates. The definition of theseterms varies but they should be used to indicate thetemperature below which foam concentrates can­not be used through induction systems. However,these figures must be treated with some cautionbecause foam concentrates above these low tem­peratures may still have high viscosity which willprevent them being picked up at the correct rate bymost foam concentrate induction systems.

Induction equipment should be checked for accu­racy both when the foam concentrate is at the low­est temperature at which it expected to be used and

trates which may lead to blockages in inductionsystems and other equipment. Mixing of incom­patible foam concentrates is also likely to lead topoor firefighting foam being produced with anassociated reduction in firefighting performance.

• When changing over from one type of foamconcentrate to another, especially in bulkstorage or fire appliance tanks, first ensurethat all of the old type has been removed,and the tank and equipment have been thor­oughly cleaned and dried before refilling.Ensure that the new foam concentrate iscompatible with the material of manufactureof the storage container.

Consequently, the ground rules to ensure thatincompatible foam concentrates are not mixedtogether are as follows:

• Do not mix together different types, grades,brands, or concentrations of foam concen­trate without first consulting the manufac­turer(s). All possible adverse effects, such asreduced shelf life, formation of sludge,reduction in firefighting performance etc.,should be explored with the manufacturerand understood. If the manufacturer(s) agreeto this mixing, it is likely that the resultingfoam concentrate mixture will tend to exhib­it the least effective properties of each of thefoam concentrates mixed.

• The chemical properties of foam concen­trates can change with time and storageconditions. Consequently, even a new batchof the same brand and grade might causedifficulties when mixed with older stockespecially if deterioration of the old stockhas taken place. Manufacturers should beconsulted if there are any doubts. Freezeprotected and non-freeze protected versionsof the same brand can be mixed but therewill obviously be a reduction in the freeze­protection of the foam concentrates.

2.2.2 Viscosity

Viscosity is a measure of how well a liquid willflow. A low viscosity is often desirable because itimproves the flow characteristics of a foam

Fuel Emulsifiers2.1.8

Fuel emulsifiers are mixtures of emulsifiers, wet­ting agents and other additives. They are generallydesigned for use at concentrations between 0.5%and 6% in water and mayor may not producefoams. They are formulated specifically for appli­cation to class B petroleum based fuels althoughsome manufacturers also recommend their use forclass A fires.

no better than water when used to extinguish firesin wooden pallets.

Fuel emulsifiers are oleophilic; in others wordsthey are 'oil liking'. Consequently, on applicationto petroleum based fuels, it is claimed that the fuelemulsifier solution mixes with the fuel to form anemulsion which consists of fuel molecules encap­sulated in water molecules. This is said by themanufacturers to significantly reduce the amountof vapour released by the fuel making the mixtureincapable of sustaining combustion. When usedagainst petroleum fuel fires, sufficient mixing ofthe emulsifier with the fuel, by very vigorousdirect application to the surface of the fuel, is saidto result in rapid knockdown and extinction of thefire. In addition it is claimed that because an emul­sion has been formed and the fuel molecules havebeen encapsulated, re-ignition should not occurand that the mixture is then suitable for disposalwith no risk of re-ignition.

On class A fires, fuel emulsifiers are claimed tosimply act as class A foams (see above).

Different types and makes of foam concentrateare not generally compatible and manufacturers'advice and recommendations should be followed.Mixing incompatible foam concentrates may causesludge and sedimentation to form in the concen-

2.2 Handling and Storage of FoamConcentrate'

2.2.1 Compatibility

Emulsifiers have only recently been introducedand their performance relative to other foam con­centrates and firefighting media has yet to beproven in the UK.

Class A Foam Concentrates

Fire Ser\'ice Manual12

Dedicated wetting agents are generally used atconcentrations of up to 1%. In addition, some film­forming and SYNDET foam concentrates intendedfor use at 3% on hydrocarbon fuel fires can be usedas wetting agents at concentrations of between0.5% and 3.0%. Wetting agents are generally rec­ommended for use in either non-aspirated or sec­ondary aspirated application through standardwater branches.

2.1.7

penetrating and spreading abilities. They may alsoprovide emulsification (see Section 2.1.8 below)and foaming characteristics. Dedicated wettingagents are available although some manufacturersof film-forming and SYNDET foam concentratesstate that these too may be used as wettingagents.

The term 'Class A Foam' originated in the USAand is used to describe foam concentrates that areprimarily intended for use on class A fires. Theyhave been in use in the USA for more than 20 yearsin fighting wildland fires but more recently theyhave been gaining in acceptance there for use instructural firefighting.

Class A foam concentrates are often syntheticdetergent foam concentrates that have been for­mulated for use on class A fires only. They areclaimed to reduce the surface tension of water toincrease its capacity to spread and penetrate classA fuels. Consequently, if this is the case, someclass A foams may also be defined as wettingagents (see above). Generally, they are formulat­ed for use at concentrations of up to 1%. Theyare mostly intended for use either non-aspiratedor secondary aspirated using standard waterbranches. Some have also found use in com­pressed air foam systems (CAFS - see Chapter 5,Section 5.4).

•

In addition to the effects of pH. surface activeagents can increase corrosion mainly due to theircleaning and penetrating properties, although otherchemical actions can also take place.

Acidic liquids are usually the most corrosive tometals and alloys, particularly those containingiron, such as carbon steel or cast iron. Strong alka­line liquids can attack aluminium and zinc.

The materials used for the construction of the con­tainers and associated fittings, pumps etc. shouldalso be carefully considered to ensure that corro­sion, and a possible reduction in firefighting per­formance, does not occur (see Section 2.2.3above).

The positioning of storage containers should alsobe a major consideration to ensure that the foamconcentrates are not subjected to temperaturesbeyond the storage limits recommended by themanufacturers (see Section 2.2.4 above).

Containers that are refilled before being complete­ly emptied may cause foam quality and firefight­ing performance problems even if the same typeand make of foam concentrate is used. The foamconcentrates may be incompatible (see Section2.2.1 above) and the mixing of different ages offoam concentrate may produce unwanted sideeffects, such as sedimentation and sludge. Ideally,containers should be completely emptied, cleanedand dried before they are refilled.

and sealed to prevent evaporation and oxidisationof the foam concentrate due to the chemical reac­tion of the concentrate with air.

The use of pressure/vacuum vents in storage tanksare also sometimes recommended in order toreduce these effects. Sealing oils can also be usedto cover the surface of the foam concentratealthough pressure/vacuum vents will still berequired.

Methods of transporting the foam concentrateand/or their containers to the fireground and thendistributing the foam concentrate to foam makingequipment also need to be carefully considered.Fixed bulk storage containers will require ade­quately specified and sized pumps and/or outlets(especially for gravity fed systems) to ensure foamconcentrate supplies are loaded into mobile unitsin the shOltest possible time. Mobile units shouldalso have adequately specified and sized pumpsand outlets to ensure quick delivery of the foamconcentrate when on the fireground. The materialsof construction of the containers and associated fit­tings on the mobile units should also be chosenwith the corrosive and other effects of foam con­centrates in mind.

Order of Use

Storage Containers and BulkStorage

2.2.5

Care should be taken to ensure that foam concen­trates are not subjected to temperatures outside ofthe ranges specified by the manufacturers. Shouldthis occur, especially over long periods of time,then it is likely to seriously impair the firefightingperformance of the foam concentrates.

for instance, some freeze protected foam concen­trates can be stored at between -29°C and 60°C.

When stored under the conditions recommendedby the manufacturer, most foam concentratesshould last at least 10 years and some shouldremain in good condition for considerably longer.The condition of stored foam concentrates shouldbe checked on a regu lar basis (see Chapter 3,Section 3.4).

Storage at constant low temperatures, in the orderof lOoC, will help to extend the shelf life of foamconcentrates.

It should be noted that some foam concentrateshave recommended maximum storage tempera­tures of 40°C. It is quite possible for temperaturesof this order to be regu larIy reached in storage con­tainers kept in direct sunlight.

Wherever possible, foam concentrates should beused in the order in which they were manufac­tured/delivered. This will help to prevent prolongedstorage of foam concentrates and unwanted effectssuch as sedimentation and sludge that may occurwith age. Writing the delivery date on the contain­ers is a simple way of keeping track of the age ofthe foam concentrates. Some manufacturers printthe date of manufacture on the container labels.

2.2.6

Manufacturers often advise that their productsshould be kept in original, sealed containers tohelp to maintain the concentrates in good condi­tion. These are often 20 or 25 litre cans, 200 litredrums or 1000 litre containers.

If original containers are not used, then the adviceis to ensure that the storage containers are kept full

Storage and Use TemperatureConditions

2.2.4

The effects of corrosion will not only lead to thegradual, or sometimes rapid, destruction of thestorage containers, but it may also lead to seriouschemical effects on the foam concentrates them­selves, possibly leading to poor foam productionand firefighting performance.

Many P, FP, AFFF and FFFP foam concentrates arefreeze protected for low temperature storage anduse. Some manufacturers state that some of theirfoam concentrates can be used when they are attemperatures as low as -29°C.

able for all but the SYNDET foam concentratewhich produced severe damage in both materials;in particular it caused the epoxy coating to peelaway from the underlying steel.

Some manufacturers produce both freeze protectedand non-freeze protected versions of their foamconcentrates. Care must be taken with the non­freeze protected versions as some of these shouldnot be subjected to freezing and their minimumuse temperature is often around 2°C.

The corrosion and chemical effects can take manyforms but a particularly serious consequence canbe the formation of particles and very viscousproducts (sludge) in the foam concentrate. Theseeffects can lead to blockages and other seriousproblems with induction systems and other equip­ment.

Manufacturers recommend minimum and maxi­mum storage temperatures for their foam concen­trates. This can be a very wide temperature range,

As mentioned previously (see Section 2.2.2above), foam concentrates generally become moreviscous the cooler they become. Consequently. theminimum use temperature given by manufacturersfor their foam concentrates is often based on theirassessment of how the viscosity of their productswill affect the induction rate. When used at, ornear, their minimum use temperature, the viscosityof some foam concentrates will be so great thatthey will not be picked-up at the correct rate bysome foam induction equipment.

Corrosion2.2.3

Firefighting foam concentrates can contain a highpercentage of water; in some the water content canbe as much as 80%. Consequently, most foam con­centrates are nearly neutral with pH values ofbetween 6.5 and 9.0. The limits of pH of a partic­ular foam concentrate are normally given by themanufacturer and are determined in laboratoriesby using pH meters.

An initial indication of how corrosive a liquid maybe can be made by looking at how acidic or alka­line it is. The measure used for this is pH which ison a scale of I to 14. If the pH of a liquid is lowerthan 7 then it is an acid; if it is higher than 7, it isan alkaline. A liquid with a pH of 7 is referred toas neutral, being neither acid nor alkaline; purewater has a pH of 7.

at 'normal' operating temperatures. With somefoam induction systems, the use of high viscosityfoam concentrates and some non-Newtonian pseu­do-plastic foam concentrates, will result in little, orno, foam concentrate being picked-up.

Foam concentrate manufacturers should always beconsulted on the best materials for use with theirproducts. However, testing (Reference 2) has indi­cated that UPVC, 60/40 brass, 70/30 brass andstainless steel may be the best materials for use instoring the types of foam concentrate most oftenused by the UK fire service (i.e. AFFF, AFFF-AR,FFFP, FFFP-AR, P, FP and SYNDET). Zinc (forgalvanising) was found to be unacceptable for thestorage of the P, FP, FFFP and FFFP-AR foam con­centrates but was acceptable for the AFFF types.Aluminium was found to be an excellent materialfor the storage of the AFFF type foam concentratesbut unacceptable for any of the others. GRP andepoxy coated materials were found to be accept-

•

14 Fire Service Manual

-Firefighling Foam - Technical 15

F-ref-gh ing FoaTechnical

Chapter

Chapter 3 - Foam Concentrate Standardsand Periodic Testing

3.1 General

Foam concentrates should be purchased that com­ply with standards that are relevant to their use bythe fire service. They should also be tested periodi­cally to ensure that they have not degraded (e.g. dueto ageing, accidental dilution or contamination).

Manufacturers usually produce their foam concen­trates to comply with one or more foam concen­trate standards. The following foam standards areoften quoted in manufacturers literature:

Standard Title

BS EN 1568 - Fire Extinguishing Media - Foam Concentrates (British/European Standard)Part I - Specification for medium expansion foam concentrates for surface

application to water-immiscible liquidsPart 2 - Specification for high expansion foam concentrates for surface

application to water-immiscible liquidsPart 3 - Specification for low expansion foam concentrates for surface

application to water-immiscible liquidsPart 4 - Specification for low expansion foam concentrates for surface

application to water-miscible liquids

ISO 7203: 1995 Fire Extinguishing Media - Foam Concentrates(International Standards Organisation)

Part I - Specification for low expansion foam concentrates for topapplication to water-immiscible liquids

Part 2 - Specification for medium and high expansion foam concentratesfor top application to water-immiscible liquids

Part 3 - Specification for low expansion foam concentrates for topapplication to water-miscible liquids

DEF STAN 42-40

DEF STAN 42-41

- Foam Liquids, Fire Extinguishing (Concentrates, Foam,Fire Extinguishing) (UK, Ministry of Defence)

- Foam Liquids, Fire Extinguishing (Concentrates, Alcohol ResistantFoam, Fire Extinguishing) (UK, Ministry of Defence)

ICAO/CAA CAP 168 - Licensing of Aerodromes, Chapter 8, Appendix 8E, Foam PerformanceLevels, Specifications and Test Procedures (UK, Civil Aviation Authority)

UL 162

MIL-F-24385

- Foam Equipment and Liquid Concentrates (USA, Underwriters Laboratories)

- Fire Extinguishing Agent, Aqueous Film-forming Foam (AFFF) LiquidConcentrate, For Fresh and Sea Water (USA, Military/Navy)

Firefighting Foam - Technical 17

3.2.1 General

3.2 Physical Property Te ts of FoamConcentrate

pH (acidity/alkalinity)

Sediment (Sludge)

Spreading Coefficient

3.2.3

3.2.4

3.2.5

Film-forming foam concentrates are formulated toform an aqueous film on the surface of somehydrocarbon liquids. Spreading coefficient is ameasure of this ability.

Sediment is a measure of the amount, as a percent­age by volume, of undissolved solids contained inthe foam concentrate. Sediment is also sometimesknown as sludge. Excess sediment can result inblockages and other serious problems with induc­tion systems and other equipment.

pH is a measurement of the acidity to alkalinity ofa liquid on a scale of 1 to 14. A pH of 7 is neutral(e.g. pure water), a pH of I is very acidic, a pH of14 is very alkaline. Measurements of pH help togive an indication of the corrosion potential of theliquids (Section 2.2.3).

Spreading coefficient

Surface tension of the foam solution

minus Surface tension of the hydrocarbon liquid

minus Interfacial tension

This is determined in a laboratory by measuringthe surface tensions of a solution of the foam con­centrate and a hydrocarbon liquid (normallycyclohexane). In addition, the interfacial tensionis also determined, by measuring the surfacetension where the foam solution (top) and thehydrocarbon liquid (bottom) meet. A calculationis then performed to determine the spreadingcoefficient of the foam solution. The calculationis as follows:

Note that although a solution of the foam concen­trate may form a film on cyclohexane, or what ever

If the spreading coefficient is positive, the foam solu­tion will form an aqueous film on that particularhydrocarbon liquid and the foam concentrate isdeemed to be 'film-fonning'. If the spreading coeffi­cient is negative, an aqueous film will not be formedand the foam concentrate is not film-forming.

Specific Gravity (RelativeDensity)

Physical property tests often include laboratorymeasurements of parameters such as pH (acidi­ty/alkalinity), viscosity, specific gravity, sedimentand the effects of accelerated ageing. Standardsgenerally contain well defined methods and equip­ment for the measurement of these properties. Theresults of these tests can be used to compare theproperties of the foam concentrate with mini­mum/maximum requirement limits set within stan­dards or with previously tested foam concentrates.

The data provided by these tests can be used bymanufacturers as bench marks for checking theconsistency of later manufactured batches of foamconcentrates (quality control).

The measurements can also be used for compari­son purposes in order to determine the condition offoam concentrates after long periods of storage(see this Chapter, Section 3.4).

A wide range of physical property tests are carriedout as part of standard approvals processes, the fol­lowing physical property tests are most oftenincluded:

Most physical property tests are relatively simpleand inexpensive to perform. Consequently, manu­facturers are more likely to can'y out physicalproperty tests than carry out fire tests as part oftheir quality control procedures. However, physi­cal property tests do not provide any useful infor­mation regarding the firefighting performance offoam concentrates.

3.2.2

Specific gravity (or relative density) is a measure ofthe ratio of the mass of a given volume of foam con­centrate to the mass of an equal volume of water.This is normally measured with the temperature ofthe foam concentrate and water at 20ne. Specificgravity can be used to determine whether a foamconcentrate has been diluted or over concentrated.

In Sections 3.2 and 3.3 of this Chapter, physicalproperty tests and fire tests are discussed in gener­

al terms.

Once the concentrate has been purchased, it shouldbe stored and used as recommended by the manu­facturer or supplier (see Chapter 2, Section 2.2).However, the foam concentrate will eventuallydeteriorate and so it is important that foam stocksare periodically tested to ensure that their perfor­mance remains acceptable. Section 3.4 of thisChapter discusses periodic testing including typi­cal physical property and fire tests that might beperformed and also provides information on thecollecting of representative foam concentrate sam­ples from storage containers.

• Physical property tests

aspirated AFFF firefighting foams for crashfire situations. US Navy typical applicationsof AFFF include incidents on the flightdecks of aircraft carriers where a quickknockdown of shallow spill fires is requiredto assist air crew survivability.

Generally, foam concentrate standards consist oftwo main areas of testing:

• Fire tests

It should be remembered that the methods andevaluation techniques used may vary considerablyfrom standard to standard. As a result, it can bevery difficult and unwise to compare resultsachieved by one foam concentr.ate when tested toone standard with those achieved by a secondfoam concentrate when tested to another standard.In addition, the results of standard (small-scale)fire tests cannot be relied upon to predict the fire­fighting performance of foam concentrates whenused on large fires.

When purchasing foam concentrates, it isimportant to have some background knowledgeof these standards in order to decide whetherthe foam concentrates complying with them arelikely to be suitable for fire service use. Ideally,the standards themselves should be obtainedand evaluated.

• The 'MIL-F spec' was designed by the USnavy to assess the suitability of 3% and 6%

• UL 162 covers foam producing equipmentand liquid foam concentrates used for theproduction and discharge of firefighting lowexpansion foam. UL is unique in that it isthe firefighting 'system' that is approved(including the foam-making branch) andnot the foam concentrate as an individual

item.

• The International Civil Aviation Authority(ICAO) specify performance standards forfoam concentrates in their document AirportServices Manual Part I 9137-AN/898 whichsupports the requirements to be met byAirport Fire Services to be compliant withICAO Annex 14, Volume one (AerodromeDesign and Operations). The UK CivilAviation Authority (CAA) has adopted theICAO foam standard in its guidance docu­ment Civil Air Publication 168 (Licensing

of Aerodromes).

Each of these standards has been produced in orderto ensure the quality of particular foam concen­trates for particular purposes:

• DEF STAN 42-41 specifies requirementsfor alcohol resistant foam concentrates, forcontrolling and extinguishing fires wheresolvents and products containing solventsare bulk stored. The standard covers AFFF­AR and FFFP-AR foam concentrates whenused at 6% concentration.

• DEF STAN 42-40 specifies requirementsfor foam concentrates for controlling andextinguishing hydrocarbon fires in aircraft.ships and vehicles, as well as for generalpurpose use. The standard covers P, FP,AFFF and FFFP foam concentrates.

• The British, International and Europeanstandards have been produced for procure­ment of all types of foam concentrateswhich meet minimum performancerequirements for general firefighting appli­

cations.

-18 Fire Service Manual Firefighting Foam - Technical 19

3.3.1 General

3.3 oam Concentrate StandardFire Te ts

What is the Application Rate?

How is the Foam Applied?

3.3.6

3.3.7

The application rate should be above the criticalapplication rate (see Chapter 7, Section 7.2) butshould not be too high. If a high application rate isused then it is likely that the fire will be extin­guished very easily, even with poor quality foamconcentrates. The application rate should certainlynot be any higher than the minimum recommend­ed application rate for spill fires given in thisManual (see Chapter 7, Section 7.3).

extinction can be aided by the dilution of the fuelwith the applied foam solution.

Most standard fire tests involving hydrocarbonsrequire there to be a depth of water (a water base)in the tray. This helps to ensure a consistent depthof fuel over the whole area of the tray and helps toprevent heat damage to the fabric of the fire tray.Fire tests involving water-miscible type fuels mustnot have water bases because these will dilute thefuel making it easier to extinguish.

Some standards involve applying foam gently viaa back-plate. Although it is recommended thatfoam should be applied gently when used opera­tionally, this is not often possible. The better stan­dards for foam concentrates for fire service use arethose which require the foam to be applied force­fully to the surface of a burning fuel, i.e. the' worstcase' situation. Forceful application is far moretesting of the firefighting capabilities of the foam,palticularly its fuel tolerance.

Some standards specify that the foam-makingbranch should be in a fixed position, others allowit to be hand-held. Fixed branches are more likelyto result in a repeatable fire test while the hand­held branch is more realistic. However, hand-heldapplications can result in variations in firefightingperformance that can be attributed more to theoperators experience and tactics than the proper­ties of the foam alone. Fixed branches have thedisadvantage that fire tests involving them willtend to favour the more fluid foams.

Generally, the test equipment used during standardfire tests makes finished foams that have lower

Is the Fuel Reproducible?

How Long is the Preburn?

How Deep is the Fuel?

3.3.3

3.3.4

3.3.5

In Europe, petrol is produced to European stan­dards that allow variations in formulation withinfairly large margins. This allows petrol to be pro­duced economically but provides a fuel whoseburning properties and effects on foam can varyconsiderably. These variations make petrol unsuit­able for use as a standard test fuel.

Preburn times (i.e. the time from ignition of thefuel until the application of foam) can vary fromstandard to standard. Short preburns are unlikelyto allow the fuel burning rate and heat output tostabilise and will not allow the tray sides enoughtime to become hot. Longer preburns are morerealistic and consequently the fires are likely to bemore difficult to extinguish. Preburns of around aminute are often used for hydrocarbon fuels. Thisis a compromise between fuel costs and fire sever­ity. Fires involving water-miscible fuels take muchlonger to stabilise and so the longer the preburn thebetter.

Is the fire test fuel manufactured to a tight enoughspecification so that the burning characteristics ofthe fires are always similar? The specifications formilitary and aviation grades of avtur and avgas canbe strict which enables them to be used as testfuels. Heptane is a very reproducible fuel and thisis the main reason why it is used as the test fuel in,many standards. Various well defined grades ofHeptane are available and the exact grade requiredfor a particular standard fire test is normally spec­ified.

For hydrocarbon fires, the fuel depth should be atleast 25mm (a spill fire - see Chapter 6, Section6.3.2) or, preferably, deeper. This is likely to be amore realistic condition for the tests and will pro­vide enough fuel for a reasonable preburn time andburnback test. However, it must be rememberedthat with an average hydrocarbon burning rate of4mm per minute, a 25mm depth of a typical hydro­carbon fuel will only burn for around 6 minutes.Fire tests involving water-miscible fuels shouldhave a much greater depth. This is because their

Is the Fuel CommonlyEncountered Operationally?

Results of standard fire tests cannot be used to pre­dict the firefighting pedormance of foams opera­tionally although they do at least indicate that thefoams can put out fires. They can also be used toensure that the firefighting performance of foamconcentrates has not deteriorated due to age, cor­rosion, contamination etc. However, this requiresthat the same test method and equipment havebeen used previously on the foam concentrate inorder to enable a valid comparison to be made.

The surface area of the test fires varies, but it isusually in the region of 0.25m2 to around 405m2.

Small standard fire tests are used by some manu­facturers for quality control purposes during pro­duction although fire tests are usually consideredto be environmentally unfriendly, inconvenient,costly and time consuming to perform.

3.3.2

performance of foam concentrates under closelycontrolled, but attificial, conditions. The results ofthese tests can be used to compare the performanceof foam concentrates with minimum/maximumrequirements within the standards or with previ­ously tested foam concentrates. Typically, timingsare recorded to 90% extinction, 99% extinction,complete extinction and 25% or 100% burnback.

When looking at the suitability of standard firetests for particular fire service related applications,the following questions should be addressed:

It should also be noted that all of the standardsreferred to in this Chapter of the Manual are forprimary aspirated foams only; there are currentlyno standards available for determining the suitabil­ity of foam concentrates for fire service secondaryaspirated use.

Petrol is the most likely fuel to be encounteredoperationally. Fuels such as avtur, avgas and hep­tane are not as volatile as petrol and are generallyeasier to extinguish. Avtur and avgas may be inregular use at airfields but are rarely encounteredelsewhere. Heptane is unlikely to be encounteredoperationally and is not representative of any fuelthat is.

Effects of Freeze/Thaw

Accelerated Ageing

Viscosity

3.2.6

3.2.7

3.2.8

Accelerated ageing is intended to determine theeffects on a foam concentrate of long term storage.The test usually involves storing a sample of thefoam concentrate at a high temperature (e.g. 60°C)for an extended period of time (e.g. 7 days). Thefoam concentrate is then allowed to cool and theeffects on the foam concentrate are measured, nor­mally by comparing before and after physicalproperty tests.

Freeze/thaw tests are used to determine the effectson a sample of foam concentrate of several cyclesof cooling it below its freezing point and thenthawing it out. Some standards require a selectionof physical property tests to be carried out after thefreeze/thaw cycle. The results of these are thencompared with measurements made before thetests; any variations must fall within certain limits.Other standards simply require observation of thesample for evidence of solids, crystals or sludge.

hydrocarbon liquid used, this does not necessarilymean it will form a film on this or any other hydro­carbon liquid under operational conditions (seeChapter 4, Section 4.4).

Standard fire tests, that is those fire test methodsthat are contained in various foam concentratestandards (e.g. British, European and Internationalstandards) are used to assess the firefighting

Viscosity is a measure of how well a liquid willflow (see Chapter 2, Section 2.2.2). Liquids aregenerally classed as either being non-Newtonianor Newtonian. A low viscosity is often desirablebecause it improves the flow characteristics of afoam concentrate through pick-up tubes, pipeworkand induction equipment. The viscosity of thefoam concentrate is usually measured either at20DC or at its minimum use temperature.

•

20 Fire Service Manual

..Firefighting Foam - Technical 21

3.3.10 When are the Fire TestsCarried Out?

Wind speed also needs to be carefully controlled,little or no wind will help to produce better, morereproducible tests and results - indoor tests arepreferred.

expansion ratios and much longer drainage times.Consequently, the foams produced are not realisticbecause they are more stable and better worked(see Chapter 4, Section 2) than foams producedthrough fireground foam-making equipment.

Collection of Foam ConcentrateSamples

3.4.2

• Three samplesOne from the top, one from the middle andone from the bottom of the container.

Foam samples sent for analysis must be represen­tative of the contents of the container from whichthey have been taken. Samples can be taken as fol­lows:

• One sampleFrom the bottom of the container only, orfrom anywhere in the container after thor­oughly mixing the contents.

• Two samplesOne from the top of the container and onefrom the bottom.

Samples should be collected in clean, seal-ablecontainers. Each sample should be at least 1 litreand should completely fill the container. Once thesamples have been collected, the collection con­tainers should be sealed and labelled with the dateand details of where the sample was taken from. Atleast two samples should be taken from each sam­pling location. One sample should be sent to thetesting organisation and the other should be keptfor further testing should this be required.

including the induction or injection equipment,pumps, typical hose lengths, procedures etc.should all be periodically checked individually,and as a whole system, to ensure that all are oper­ating cOlTectly and ultimately providing finishedfoam of the required quality.

Care should be taken when collecting from thebottom of a container due to the possible accumu­lation of sediment from rust and degradation

Do not write on the sample container the type andconcentration of foam concentrate that is in thecontainer, the testing organisation should be ableto determine this from the results of their tests. Ifthis information differs from the actual contentsthen it is an indication that further investigations ortests may need to be carried out to identify thecause of the discrepancy.

If the foam concentrate complies with a particularstandard, then the limits specified within the stan­dard can also be used to determine whether thefoam concentrate still complies with the standard.

• The results of the routine quality controltests originally carried out by the manufac­turer during production on the particularbatch or batches of foam concentrate to betested. This information will normallyinclude the results of physical property testsand, in some instances, the results of firetests. All manufacturers gather quality con­trol test data during production and they wi 11normally make it freely available on requestat the time of purchase. However, in orderto make the best use of this information,it is extremely important that batch num­bers are recorded on storage containersand accurate records of usage are kept.

more than one manufacturer in order to obtain sev­eral test reports for comparison.

Independent test houses offer an alternative meansof having foam concentrates tested. However,before allowing them to carry out work, alwaysensure that they have previously analysed foamconcentrates and that they can carry out the fullrange of tests to the required standard.

• The manufacturer's data sheet (from thetime of purchase) for the particular foamconcentrate to be tested.

In order for the amount of deterioration that hastaken place to be quantified, it is necessary tohave:

As long as the same test methods and equipmentare used, the results of periodic testing of storedfoam concentrates can be compared with the limitsset out in the manufacturers data sheets and withthe actual peJformance of the foam concentratewhen originally produced. Any discrepancies canthen be identified and investigated further.

It should be remembered that foam concentratesare only part of the equipment and resources nec­essary to produce effective firefighting foams.Consequently, the whole foam-making system,

•

•

3.4.1 General

3.4 Periodic Testing of FoamConcentrate

• Carry out testing at brigade level.• Return a sample to the supplier.• Send a sample to an independent laboratory.

There are a number of ways of having periodictesting calTied out. these include:

Regular fire testing can indicate the continuingsuitability of foam concentrates for that task.Some standards only require the fire tests to becarried out once, at the approval stage.Conformance with the standards is then onlychecked via physical property tests - probably bythe manufacturer.

Storing foam concentrates as recommended by themanufacturers and as described in Chapter 2,Section 2.2, will help to maintain them in a usablecondition. However, no matter how well they arestored, deterioration will take place. Consequently,it is important that samples of stored foam concen­trates are tested periodically (e.g. annually) toensure that they have not significantly deterioratedand that they remain able to effectively extinguishfires.

The range of tests that should be carried out toevaluate the condition of foam concentratesrequires some specialised equipment and technicalexpertise. It would not be cost effective or practi­cal for individual brigades to carry out the fewtests that would be required each year.

Most foam concentrate manufacturers will carryout this type of testing for a fee. However, someorganisations consider it undesirable to rely onmanufacturers tests when the manufacturer has aclear commercial interest in the outcome. Whilstthere is no suggestion that any supplier hasfalsified results, it is always possible that anindividual could act upon misplaced zeal in thefuture.

Some manufacturers will test any foam concen­trate, not just those they produce. Consequently, iffunds allow, it may be advisable to send samples to

Under What Conditions are theFire Tests Performed?

What Burnback Test is Used?

33.8

The test equipment only produces primary aspirat­ed foam for use during the standard fire testsreferred to in this Chapter of the Manual; there arecurrently no standards available for directly deter­mining the suitability of foam concentrates forfire service secondary aspirated use.

Fuel, foam solution, air and fuel temperaturesshould all be tightly controlled in order for the firetests to be repeatable and to enable the results to besatisfactorily compared with previous tests. Largevariations in temperature can lead to very differentextinction and burnback results. Cooler tempera­tures are likely to lead to quicker extinction timesand longer burn back performances.

33.9

In order to test the security of the foam blanket, aburnback test is required. Burnback tests, wherethe burnback flames are near to, or actuallyimpinge on, the foam blanket are much more test­ing. Burnback tests which also involve a burningfuel in a metal container can help to assess thesealing capabilities of foam blankets against veryhot materials.

Are the fire tests only carried out when the foamconcentrate is initially tested for compliance withthe requirements of a standard or are they carriedout on a regular basis (i.e. each manufacturedbatch/quality control)? Are/were the fire tests car­ried out by an independent test house or were theycarried out by the manufacturer?

•

22 Fire Service Manual

...Firefighting Foam - Technical 23

(b) pH (Acidity/Alkalinity)

(a) Specific Gravity (Relative Density)

products. This sediment should be prevented fromentering the sample container as it may lead to testresults that are not representative of the whole con­tents of the container.

(see this Chapter, Section 3.1). This size of firetest is also recommended for quality control useduring foam concentrate production in the British,European and International standards for firefight­ing foam concentrates (see this Chapter, Section3.1). However, the main difference is that the MoDtests involves the use of avgas or avtur as fuel andthe British, European and International standardsuse heptane (see this Chapter, Section 3.3 forinformation on test fuels). In order to make thebest use of fire test information it is necessary tohave previous fire test data available so that truecomparisons can be made. For instance, if batchfire test data was available for the foam concen­trate when originally purchased then, as long as thesame fuel, test methods and equipment are usedwhen testing the stored foam concentrate, the firetest results can be compared for obvious differ­ences in performance. If original fire test data isnot available, but the foam concentrate conformedto a particular foam standard when produced. thenthat standard fire test could be carried out to deter­mine whether the stored foam concentrate tillcomplies with that standard.

Periodic Fire Tests3.4.4

Any fire tests of stored foam concentrate samplesthat are carried out by manufacturers or indepen­dent test houses are likely to involve significantcost. However, it should be remembered that themain reason for using foam concentrates is toextinguish fires and so this type of testing is thebest way of determining whether the foam concen­trate remains suitable for its purpose.

Film-forming foams which no longer provide apositive spreading coefficient when measuredhave either been contaminated or have significant­ly degraded. See this Chapter. Section 3.2.5 formore information on spreading coefficient.

(d) Spreading Coefficient

When stored correctly. foam concentrates shouldonly contain very small amounts of sediment.High levels of sediment can indicate that the foamconcentrate has been contaminated in some way(e.g. mixed with other foam concentrates), hasbeen broken down by micro-organisms and/or hasdegraded due to incorrect storage. See thisChapter, Section 3.2.4 for more information onsediment.

Consequently, care should be taken when obtain­ing samples from the bottom of a container toensure that a representative sample is obtained (seeabove). The maximum sediment content of a foamconcentrate is normally stated in the manufacturersdata sheet.

Typical Physical Property Tests3.4.3

If only one sample is to be tested, then it ispreferred that this should be drawn from the con­tainer after the contents have been thoroughlymixed together.

Although a wide range of tests may be carried out,typically, the following physical property tests willbe included when manufacturers and test housesdetermine the condition of stored foam concentrates:

The limits of specific gravity for foam concen­trates are normally stated in the manufacturers datasheets. Specific gravity measurements that arehigher than the manufacturers limits indicate thatthe foam concentrate has become more concentrat­ed, probably due to evaporation. Measurementsthat are below the manufacturers limits indicatethat the foam concentrate may have been dilutedby water in storage, dilutions of greater than 10%may require that all of the foam concentrate in thecontainer be replaced. Changes in the specificgravity of foam concentrates may also indicatedilution or contamination by other substances. Seethis Chapter, Section 3.2.2 for more informationon specific gravity.

The limits of pH for foam concentrates are nor­mally stated in the manufacturers data sheets. pHvalues outside of these limits can indicate that thefoam concentrate has been contaminated in someway (e.g. mixed with other foam concentrates),has been broken down by micro-organismsand/or has degraded due to incorrect storage. Seethis Chapter, Section 3.2.3 for more informationon pH.

(c) Sediment (Sludge)

Sediment will tend to sink to the bottom of con­tainers when stored over a long period of time.

Although the physical property tests discussedabove will indicate possible changes in the consis­tency of the foam concentrates, it is the firefight­ing performance that is of most interest. If thephysical property tests indicate a problem, then afire test should be considered in order to investi­gate the effects of this on the firefighting perfor­mance of the foam concentrate.

The fire tests performed by manufacturers and testhouses on a routine basis are generally based on, oraround, methods and equipment specified in foamconcentrate standards. Typical of this is the 0.25m2

area tray fire test specified within the UK Ministryof Defence (MoD) foam concentrate standards •

24 Fire Service Manual Firefighting Foam - Technical 25

•

Chapter 4 - The Properties ofFinished Foams and The Effects ofThese on Firefighting Performance

4.1 General

F refighting FoamTechn·ca

4Chapter

the compatibility of various finished foamswith each other and with dry powders

finished foam quality,

the typical firefighting characteristics ofeach of the individual types of foamidentified in Chapter 2, particularly whenused on liquid hydrocarbon fuel fires.

• the suitability of finished foams for baseinjection,

Also included are:

• Foam blanket stability/drainage time: anindication of how well the finished foamblanket retains its liquid content and hencehow 'stable' and long lasting it is.

••

•

Flame knockdown: the ability of thefinished foam to quickly knockdownflames and control the fire.

Extinction: The ability of the finishedfoam to extinguish the fire.

Burnback resistance: the ability of thefinished foam, once formed on the fueLto stay intact when subjected to heatand/or flame.

In Chapter 2, the various types and properties offoam concentrates were discussed. This Chapterexplains some of the more important properties offinished foams. These properties can greatly affectthe firefighting performance of finished foams interms of:

•

••

)1

The properties discussed in this Chapter include:

• Working: the effort required in mixing airwith the foam solution to produce a usablefinished foam.

• Foam flow/fluidity: the ability of thefinished foam to flow over the surfaceof a fuel and around obstructions.

It should be remembered that other factors, such astype of fuel, equipment and application methods,also have a considerable effect on the performanceof finished foams. These areas are discussed inlater Chapters and the operational aspects ofapplying foam are discussed in Volume 2 of theManual.

4.2 Working

•

•

•

Film formation: the ability of the finishedfoam to form a film that spreads over somehydrocarbon liquid fuels.

Fuel tolerance: the ability of the finishedfoam to resist mixing with, and hencecontamination by, the fuel.

Edge sealing: the ability of the finishedfoam to seal against hot metal surfaces.

"Working" refers to the action of the internal partsof foam-making equipment on the foam solutionstream as it passes through the equipment. Theinternal parts can include gauzes and baffles whichobstruct the flow of the foam solution and greatlyassist in the mixing in of air. This helps to produceuniform sized, stable, foam bubbles of acceptabledrainage and expansion characteristics.

Some manufacturers claim that, for some lowexpansion foams such as P and FP, complete for-

• ...Firefighring Foam - Technical 27

The thinness of the film, and the uncertainty of itsformation, makes film-forming foams unsuitablefor vapour suppression unless a thick foam blanketis also present. For vapour suppression, primaryaspirating equipment will provide a better protec­tive foam blanket than secondary or non-aspiratingequipment.

foams used secondary aspirated. Also, the burn­back performances of the primary aspirated foamswere vastly superior to those of the secondaryaspirated foams.

Some foam manufacturers say adequate vapoursuppression can be achieved using secondary aspi­rating equipment with film-forming alcohol-resis­tant foam concentrates. However, they claim thatthese should be used at 2 to 3 times their recom­mended concentration for application to hydrocar­bon liquids (e.g. used at 9% concentration insteadof their recommended 3%). However, mostbrigades are unlikely to have equipment capable ofproportioning at rates higher than 6%.

4.5 Fuel Tolerance

It should be noted that the standard film-formingfoam concentrates (i.e. AFFF and FFFP) formfoam blankets that drain rapidly in order to quick­ly form films on the fuel surface. Consequently,these foam blankets will need to be replenished atvery frequent intervals if adequate vapour suppres­sion is to be maintained. Primary aspirated alcoholresistant film-forming foams require less frequentreplenishment due to their much longer drainagetimes.

P foams have poor fuel tolerance and hence sufferfrom severe fuel contamination when vigorously

Fuel tolerance describes how resistant a foam is tomixing with a fuel during application. In general,foams should be applied as gently as possible tothe surface of a fuel to reduce the amount of mix­ing that takes place. Plunging a foam streamdirectly into a fuel will cause fuel to be mixed inwith the foam. If a fire is present, then it isinevitable that this foam and fuel mixture will burncausing partial destruction of the foam blanket.However, some foams are more resistant to mixingwith fuel than others.

It is important to note that although alcohol resis­tant foams produce aqueous films on some liquidhydrocarbon liquids, they do not produce them onwater-miscible liquids.

It must be stressed that film formation does nottake place on all hydrocarbon fuels. In such cases,these foams must rely on the normal extinguishingmechanisms of foam blankets. That is to excludeair from the fire, reduce evaporation and generallycool the fire. This may require more foam to beapplied, for a longer period of time than wouldnormally be expected when using a film-forming

foam.

As mentioned above, the ability of a foam to forma film on a hydrocarbon liquid can be determinedby measurements of the surface tensions of thefoam solution and the hydrocarbon liquid. Thesemeasurements are usually canied out in a labora­tory. However, in firefighting situations, the condi­tions are likely to be very different. This makes theconclusions of laboratory measurements generallyinapplicable to most practical applications of film­forming foams (see Chapter 3, Section 3.2.5).

Aqueous films offer little or no burnback protec­tion and, in any case, it can be impossible for fire­fighters to see where the transparent surface filmremains intact and where it has been broken.

60°C. Consequently, these thin films are unlikelyto help in extinguishing fires in many flammablefuels that have had long preburns.

Film formation is a very controversial area of fire­fighting foams. Some firefighters insist that firescan be seen to be controlled and extinguished wellahead of any foam blanket formed; others say thatthey have seen no evidence of the effects of filmformation.

The manufacturers of film-forming foam concen­trates often state that they may be used primaryaspirated, secondary aspirated or non-aspirated forapplication against hydrocarbon liquid fuel fires.

Petrol fire tests canied out using UK fire serviceequipment and tactics (Reference 3) found that pri­mary aspirated film-forming foams extinguishedthe fires in half of the time taken by the same

4.4 Film Formation

Protein and f1uoroprotein foams tend to be stifferand hence they give higher shear strength mea­surements than SYNDET, AFFF, AFFF-AR, FFFPand FFFP-AR finished foams. However, the shearstrength of finished foam also depends on theamount of working provided by the branch used toproduce the foam (see above). Secondary aspirat­ed equipment will produce foam of low shearstrength while primary aspirated equipment willproduce foam of significantly higher shearstrength. In addition, in primary aspirated equip­ment, the more working that takes place, the high­er the shear strength of the finished foam

The term film formation is often used and appliesto AFFF, AFFF-AR, FFFP and FFFP-AR foamconcentrates. Under certain conditions, the foamsolutions and finished foams produced from thesefoam concentrates have the ability to produce anaqueous film which spreads over the surface ofsome liquid hydrocarbon fuels. On these particularfuels, the film is said to help cool the surface of theburning liquid to reduce the hydrocarbon evapora­tion rate, seal in the vapour at the surface of thefuel and hence deplete the supply of fuel to theflames. Consequently, they may assist in theknockdown and extinction of fires in these partic­ular fuels.

The fluorocarbon surface active agents and foam­ing agents that combine to produce film-formingfoams produce a foam solution that has a very lowsurface tension. This allows a thin film to beformed on, and to spread across, some liquidhydrocarbon fuels. The main factor which influ­ences the effective formation of this film on ahydrocarbon is the slllface tension of that hydro­carbon. Film-forming foams tend to be much moreeffective on liquid hydrocarbons that have a muchhigher surface tension than the foam solution.High surface tension fuels include kerosene, dieseloils and jet fuels.

The aqueous films produced are extremely thin,typically less than a quarter of a millimetre thick,and are unlikely to form on the sUli'aces of any hotfuels. Some research carried out in America hasindicated that film formation does not occur onaviation gasoline when at temperatures above

Fire Service Manual Firejighting Foam - Technical 29 I----------------------------------_...._------------------------------------------------

Finished foams that rapidly flow across the surfaceof fuels and around obstructions can lead to quickflame knockdown and control of a fire. This can beparticularly important in aircraft or vehicle crashfire situations where there is a significant risk tolife.

4.3 Foam FlowlFluidity

Some foam solutions produce bubbles more readi­ly than others. For instance, SYNDET, AFFF andFFFP foam solutions require less working andhence foam of adequate quality can be producedusing shorter branches than are required by P or FPfoam solutions. Ultimately, if foam working isexcessive, the foam becomes very stiff and losesits flow qualities; for film-forming foams, this mayimpair there ability to produce an aqueous film onthe surface of hydrocarbon liquids. If not enoughworking is achieved, the foam will be very quickdraining, have poor stability and be made up offoam bubbles of irregular size.

Working slows down the foam stream within thebranch due to the energy required to produce foam.Consequently, the more a foam is worked within abranch, the less the distance it can be projected.

mation of stable foam bubbles should take approx­imately 1I30th of a second. However, foam solu­tion does not begin to form bubbles until it hits theside walls or obstructions approximately half wayalong the length of the branch. Consequently, it isclaimed, the foam solution should be in the branchfor a total of 11 15th of a second to form stable fin­ished foam. For main line use at flows of approxi­mately 225 Ipm, a low expansion foam-makingbranch in excess of I metre in length would berequired to give the required pass through time.

Critical shear strength is a measure of the degreeof 'stiffness' of finished foam and gives an indica­tion of its ability to flow. Shear strength is mea­sured by a paddle type torsion wire viscometer.These are specialist items of equipment and are notsuitable for routine fire service use. Shear strengthfigures can only be reliably compared if the sametype of measuring equipment and measurementmethods are used. However, these measurementsdo not provide a reliable indication of the fire­fighting capability of foams.

28

•

= Expansion

25% of Liquidcontent of Foam

Foam2000cc

FoamSolution2000cc

Weight of agiven Volume

of Foam Solution

Weight of sameVolume of Foam

1 Expansion Test

2 Drainage Time Test

Figure 4.1 Diagram showing tests to determine foam

properties.

(1) Expansion test.

(2) Drainage time test.

4.9 Burnback Resi tance

It is extremely important that foam blankets pre­vent fuel vapour percolating through to their uppersurface. If the foam blanket is unable to preventthis, then it is likely that the vapour will continueto bum on the surface of the foam. This can quick­ly lead to the complete destruction of the foamblanket.

4.8 Vapour Suppression

Figure 4. J shows the basic principles of measuringlow expansion foam expansion ratios and drainagetimes. The current British Standards for foam con­centrates (see Chapter 3) should be referred to forexact details of equipment and test methods to beused. Expansion ratios and drainage times of fin­ished foams can only be reliably compared if thesame type of foam concentrate, measuring equip­ment, foam-making equipment and measurementmethods are used. In particular, the height of themeasurement container has a significant impact onthe length of drainage time measurements; shortcontainers give short drainage times, tall contain­ers give longer drainage times.

Firefighters should remember that when a foamdrains, its volume will seem almost unchanged.Although its integrity may appear good, its fireresistance will be low as it will have lost much ofits foam solution content.

the time taken for 25% of the original foam solu­tion content (by volume) to drain from the finishedfoam. For medium and high expansion foams,50% drainage times are normally given.

Bumback resistance is the ability of a foam blan­ket to resist destruction from direct contact withheat and flames. Such contact occurs during initialfoam application where the foam blanket will becontinually covering, and moving against, flame.It can also occur, once successful foam applicationhas been achieved, from a small area of sustainedburning or from a new ignition source.

Bumback resistance is one of the main propertiesassessed when testing the firefighting performanceof foams. Usually, once a test fire has been extin­guished, the burnback resistance of the foam

A short drainage time tends to indicate that the fin­ished foam loses its water content quickly and ren­ders it vulnerable to high temperature flame andhot surfaces. AFFFs and FFFPs tend to have lowdrainage times and poor heat resistance.

Foams which have a good resistance to heat tendto exhibit good extinguishing performances andbum back resistance and therefore should havegood edge sealing properties. However, when hotmetal surfaces (i.e. in excess of lOOGC) are encoun­tered by a foam blanket, destruction of the foamblanket is inevitable and steps should be takenwhere possible to cool these surfaces sufficientlyto ensure edge sealing can take place. This can beparticularly important when fighting large tankfires.

4.7 Foam Blanket Stability/Drainage Time

Drainage time is a measurement of the rate atwhich foam solution drains out of finished foamand hence provides an indication of the stability ofthe foam blanket. Drainage time is often used tocompare the quality of various finished foams,however, it does not provide a reliable indicationof the firefighting capability of foams.

A long drainage time, and hence slow loss of waterfrom the finished foam, tends to indicate that thefinished foam is capable of maintaining its stabili­ty and heat resistance. This is usually the case withmost P, FP, AFFF-AR and FFFP-AR foams.However. this is not true for low expansion SYN­DET foams which generally produce finishedfoams with long drainage times but have very poorheat resistance.

The drainage times of finished foams depends notonly on the foam concentrate but also on the foam­making equipment used to produce it. Secondaryaspirated equipment will produce finished foamswith short drainage times while primary aspiratedequipment will generally produce finished foamswith significantly longer times. In addition, in pri­mary aspirated equipment, the more working thattakes place, the longer the drainage times.

Drainage for low expansion foams is usuallyexpressed as 25% drainage time. This is defined as

The fuel tolerances of FP and FFFP foams are con­siderably better than that of P foams. This is due tothe addition of fluorocarbon surface active agents,which are oleophobic (i.e. they repel oil) and havea very low surface tension. These properties helpto resist the spread of fuel across foam bubbles andhence increases their fuel tolerance.

applied to a fuel. This is because the surface ten­sion properties of protein foam allows fuel tospread over and within the blanket. This can resultin burning within the blanket continuing over along period of time.

In the case of synthetic detergent based foams, thehydrocarbon surface active agents that are used intheir formulation tend to emulsify oils with water.This causes the foam to pick up large quantities offuel which can readily ignite. Fuel tolerance hasbeen improved in the case of AFFFs and AFFF­ARs by the additional use of a high proportion offluorocarbon surface active agents.

In contrast to the above, fuel emulsifiers (seeChapter 2, Section 2.1.8) are oleophilic (i.e. theyattract oil) and rely on mixing well with fuel inorder to form an emulsion. The emulsion isclaimed by the manufacturers to consists of fuelmolecules encapsulated in water molecules. This,they say, significantly reduces the amount ofvapour released by the fuel making the mixtureincapable of sustaining combustion. The vigorousapplication of emulsifiers directly to fires in petro­leum based fuels is claimed by the manufacturersto result in rapid control and extinction. In addi­tion, because the fuel molecules have been encap­sulated, they say that it is unlikely that re-ignitionwill occur. Emulsifiers have only recently beenintroduced and their performance relative to otherfoam concentrates and firefighting media has yetto be proven in the UK.

4.6 Edge Sealing

The term edge sealing relates to the ability of afoam blanket to seal against hot metal surfaces. Hotmetal surfaces can cause breakdown of a foamblanket due to the boiling off of its water contentand increased vapour release from the fuel at thehot surface. This can result in the inability of a fin­ished foam to fully extinguish fires at this interface.

30 Fire Service Manual Firejighting Foam - Technical 31

• b

bLanket is assessed. Either a small area of foam isremoved and the fuel underneath is re-ignited or, aflame is continuously played on to a small area ofthe foam blanket. The measurement made isknown as the burnback time. This is the time takenfrom re-igniting the fuel, or applying flame to thefoam blanket, until the re-involvement in flame ofan area of the surface of the fuel.

Often, it is the 25% burnback time that is quotedfor the burnback resistance of foams. This is thetime it takes for a 25% area of the fuel surface tobecome re-invoLved in flames. The longer the 25%burnback time, the better the burnback resistanceof the foam blanket.

Some foams, such as P, FP and the alcohol resis­tant film-forming foams have significantly greaterburnback resistance, and hence give longer burn­back times, than AFFF, FFFP and SYNDET.

Generally, the more foam applied to a fire afterextinction has occurred, the better the burnbackresistance will be. However, if a foam blanket isleft over a period of time and allowed to drainwithout being replenished, the burn back resistanceof the blanket will be significantly impaired.

4.10 Water-mi cible FuelCompatibility

Alcohol resistant foam concentrates have beendeveloped to deal with fires involving water-mis­cible liquids such as alcohols and some petrolblends containing high levels of aLcohols and othersimilar fuel performance improvers. These, andthe finished foams that they produce, are describedin Chapter 2, Section 2.1.4.

4.11 Suitability For Subsurface(Base) Injection

Some finished foams can be introduced, via spe­cial equipment, into the bases of large storagetanks. The foam then floats to the surface of thecontents of the tank. This has the advantage thatthe finished foam is not carried away by theupdraught created by large fires and is not deterio­rated by flames on the way to the surface of thefueLs. However, foams that are used for subsurfaceinjection need to have a high toLerance to fuel con-

tamination otherwise the foams wouLd burn awayimmediately on contact with the flames on the sur­face of the product.

Subsulface injection can only be used in tankscontaining certain hydrocarbon fuels; it cannot beused for tanks containing water-miscible fueLsbecause, even with alcohol resistant foams, thesefuels will destroy the foam bLanket on contact anda foam blanket will not form. In addition, this willmean that the polymeric skin cannot form on thesurface of the fuel (see Chapter 2, Section 2.1.4).

FP, FFFP, FFFP-AR, AFFF and AFFF-AR foamsare generally considered suitable for base injec­tion.

4.12 Quality of inished Foam

The production of good quality finished foamdepends on:

• the use of a suitable type and quality offoam concentrate for the task in hand;

• foam concentrate in good condition due tocorrect storage;

• foam concentrate used at the COlTectconcentration;

• good design and choice of equipment;• good maintenance of equipment;• correct pump pressure and foam solution

flow for the equipment in use.

Drainage times and expansion ratios (and some­times shear strength) can be measured and com­pared to provide an immediate indication of the'quality' of a finished foam. Often, firefighters willlook at and feel the finished foam produced bytheir equipment and give an immediate assessmentof its quality. 'Wet' foams, i.e. those with shortdrainage times, are often refelTed to as being ofpoor quality while those that are 'dry', i.e. thosewith long drainage times, are referred to as beingof good quality.

However, there is no overall definition of a 'good'quality foam. This really depends on which foamis being assessed and its intended use.

On some fuels, AFFFs and FFFPs rely on being'wet' to assist in the formation of a fiLm on the

surface and for quick cooling. It can also assist ingiving them quick control and knockdown capa­bilities. P and FP finished foams are often betterused 'dry' to provide acceptable knockdown andextinction performance and good burn back resis­tance. If used too 'wet', by applying them via poorfoam-making equipment for instance, these foamsare likely to give very poor firefighting perfor­mance. Applying them too 'dry' will result in verythick foam being produced which does not flowvery easily and again results in very poor firefight­ing performance.

As part of the routine checking of the operation ofa foam-making system, expansion ratios anddrainage times of the finished foam can be mea­sured and compared with previous measurements.

Figure 4.1 shows the basic principles of measuringlow expansion foam expansion ratios and drainagetimes. The current British Standards for foam con­centrates (see Chapter 3) should be refelTed to forexact details of equipment and test methods to beused. Drainage times ancl expansion ratios canonly be reliably compared if the same type of foamconcentrate, measuring equipment, foam-makingequipment and measurement methods are used.

4.13 Compatibility of FinishedFoams

4.13.1 With Other Finished Foams

Generally speaking, all types of finished foam canbe used together on a single fire, although theorder of application may affect their performance.For example, film-forming foam would be betterapplied first for a quick knockdown and extinctionof a hydrocarbon fuel fire followed by an applica­tion of FP foam to provide good burnback resis­tance. Applying these foams in reverse orderwould result in the partial breakdown of the FPfoam blanket, and hence reduced burnback resis­tance, due to the film-forming foam blanket quick­ly draining with the resulting falling liquiddroplets bursting the FP foam bubbles.

4.13.2 With Dry Powder

Some finished foams will react unfavourably withcertain fire extinguishing powders if used at the

same incident. The manufacturer should be askedwhether there are any particular incompatibles totheir product. Firefighters should remember toconsult the industriallMOD/CAA brigades etc., intheir areas, as well as neighbouring local authoritybrigades where appropriate, to find out what drypowder types they are using. Foam concentratemanufacturers should then be contacted for adviceon compatibility.

4.14 Typical Characteristicsof Finished Foam

4.14.1 General

The following Sections highlight the typicalcharacteristics of low expansion finished foamsproduced from each of the main types of foamconcentrate described in Chapter 2. These charac­teristics relate mainly to their use on hydrocarbonliquid fuel fires although other comments are madeconcerning, for instance, their compatibility withwater-miscible fuels. The terms used here havebeen explained earlier in this or the previousChapters, see also the Glossary of Terms.

Table 4.1 overleaf enables a quick comparison to bemade of the typical firefighting related characteris­tics of low expansion finished foams made fromeach of the main foam types. The contents of thistable are intended to provide information on typicalperformance during general fire service use, in par­ticular, when used against hydrocarbon spill fires.

The table should be read in conjunction with thecontents of the remainder of this Section whichprovide more details of the characteristics for eachfoam type. In addition, some comments regardingthe suitability of different foam concentrate typesfor use in tackling storage tank fires are given inVolume 2 of the Manual.

It should be remembered that there are many com­panies manufacturing each of the different foamconcentrate types. The quality of foam concen­trates produced will vary from manufacturer tomanufacturer and often different quality versionsof the same foam type will be available from thesame manufacturer. Consequently, the followingSections indicate the typical characteristics of fin­ished foams prod uced from each of the foam types.

32 Fire Service Manual Firejighling Foam - Technical 33

L ....-. ......01

Table 4.1: Typical Characteristics of Low Expansion Finished Foam

Low expansion FFFP finished foams tend to havethe following useful characteristics:

and the following disadvantages:

(c) FFFP

(d) Synthetic (SYNDET)

• poor at sealing against hot objects;• poor foam blanket stability and very quick

foam drainage times;

• poor burnback resistance;• poor vapour suppression;• unsuitable for use with water-miscible

fuels.

FFFPs were designed to exhibit a combination ofAFFF and FP characteristics. The intention was toproduce a foam concentrate that had the knock­down and extinction performance of AFFFcombined with the good burnback resistance char­acteristics of tluoroprotein. However, fire tests(Reference 5) have indicated that although lowexpansion FFFP gives similar firefighting andburnback performance to AFFF, the burnbackperformance is greatly inferior to that achieved bytluoroprotein and is generally not much better thanAFFF.

SYNDET finished foams are versatile in that theycan be used for firefighting at low, medium andhigh expansion. In the UK, they are mainly used atmedium and high expansion foams.

• usable foam can be produced with minimalworking, manufacturers suggest that they canbe used primary and secondary aspirated;

• flow quicker than P and FP foams overliquid fuel sUlfaces, quickly reseal breaksin the foam blanket and flow aroundobstructions. This often results in veryquick fire knockdown and extinction.On some liquid hydrocarbon fuels, thesecharacteristics may be enhanced by thefilm-forming capabilities of FFFP;

• suitable for subsurface (base) injection;• moderate resistance to fuel contamination

although not as fuel tolerant when used onnon-water-miscible fuels as alcohol resis­tant film-forming foams or FP foams;

(b) FP

and the following disadvantages:

• very slow flowing and stiff, protein foamsdo not quickly reseal breaks in the foamblanket or seal around obstructions, Theseare some of the major reasons for the slowfire knockdown and extinction performanceof protein foams;

• very poor fuel tolerance when appliedforcefully to the surface of a fuel. This isthe main reason for very slow fire knock­down and extinction pelformances;

• unsuitable for use with water-miscible fuels;• unsuitable for subsurface (base) injection.

Low expansion finished foams produced from FPfoam concentrates tend to have the following use­ful characteristics:

• do not flow as well as film-forming foams.This often results in slower knockdown andextinction performances when compared tothose of film-forming foams;

• require to be well worked to makeacceptable finished foam, they must beused primary aspirated;

• unsuitable for use with water-miscible fuelsalthough alcohol resistant FP is availablefor certain specialised applications.

• flow quicker than P foams over fuelsurfaces, reseal breaks in the foam blanketand seal around obstructions. Theseproperties assist in producing fireknockdown and extinction performancesthat are quicker than that achieved by P;

• good fuel tolerance so they can beapplied reasonably forcefully if absolutelynecessary;

• produce acceptable fire knockdown andextinction performance although generallyslower than film-forming foams;

• good sealing properties against hot metalsurfaces;

• form stable foam blankets with slow foamdrainage times;

• very good burnback resistance;• very good vapour suppression;• suitable for subsurface (base) injection;

= Good;= Poor;= Loll' Expansion;= High Expansion;

AFFF AFFF-AR

No No

JJJJ

Yes Yes

JJJ JJ]J

JJJJJ JJJJ

JJ JJJJ

JJJJJ JJJJ

J:OJJ

JJ JJJJ

JJ JJJJ

LX LXMX MXSA SA

No Yes

Yes Yes

)]]]

!JJLXHX

No

No

J

No

No

LXMXHX

JJJJ

J

JJJJJ

JJ

JJ

JJ

Yes

No

JJJJ

JJJJ

JJJJ

JJJJJ

:OJJ

= Very Good;= Acceptable;= Very poor= Medium Expansion;= Secondary Aspirated

JJJJJJ]

MXSA

grades alld the level of repeatability of the tests.Howevel~ where there is a difference ill pelformallceof two or more grades, the difference is significant.

The firefir;hting pelj'ormance contents of this table are basedon the remits of work carried out by the Home Office FRDGon petrol spill sites.

and the following disadvantages:

• provide acceptable sealing against hotmetal surfaces;

• form stable foam blankets with slow foamdrainage times;

• good burn back resistance;• good vapour suppression;

• can be used to produce low expansionfoam only;

• require to be well worked to make accept­able finished foam, they must be usedprimary aspirated;

-- --- ---- -----

LX LX LXMX MX MX

SA SA

No No Yes

Yes Yes Yes

-- --- ---- -----

QJJJ JJJ

JJJ JJJJ

JJJ JJJJJ JJQJ

:0 JJ:O JJ

P FP FFFP FFFP-AR SYNDET

FOAM TYPE

-- --- ---- -----

No No Yes

Yes Yes No

J

J

J

J JJJJ

JJJ :rm JJ

JJJJ ]JJ]] JJ JJJJ

J]] JJJJJ JJ JJJJ

Requires to be well 'worked'?

Film-forming on some hydrocarbon liquids?

Hydrocarbon Fuel Tolerance

Foam Flow/Fluidity

CHARACTERISTIC

Edge Sealing

Flame Knockdown

Burnback Resistance

Extinction

Vapour Suppression

Foam Blanket Stability/Drainage Time

Foam Application LX

Water-miscible Fuel Compatible? No

Suitable for Hydrocarbon Subsurface Injection? No

Notes to Table 4.1:This table summarises the typical characteristics that canbe expected from good quali(v loll' expansion finishedfirefighting foams when used to fight some flammablehydrocarbon liquidjilel spillfires. The characteristics offinishedfoam will vary depending onj(lctors such asfuel.application technique, equipment and the quality of thefoam concentrate used. The firefighting pelformance con­tents of this table are based on the results of work carriedout on petrol spill fires (Reference 5). A difference inpeljormance of one grade is not significant due to thetight cut off points in the results used to generate the

4.14.2 Individual Foam Characteristics

(a) P

Low expansion finished foams produced from Pfoam concentrates tend to have the following use­ful characteristics:

Good quality foam concentrates may have bettercharacteristics, those of bad quality foam concen­trates may be considerably worse. Obviously,other factors such as fuel, application techniqueand the type of equipment used will also greatlyaffect these characteristics.

34 Fire Service Manual Firefighting Foam - Technical 35

• b

The following comments mainly relate to their useat low expansion in order to enable a comparisonto made with all of the other foam types discussed.However. many of these comments are also rele­vant for their use at medium and high expansion.

Low expansion SYNDET finished foams tend tohave the following useful characteristics:

• produce acceptable foam with minimalworking, must be used primary aspirated;

• quick-flowing which can assist in produc­ing quick fire knockdown. Medium andhigh expansion SYNDET foams do notflow as readily, however, the large volumeof foam produced can achieve quickknockdown and extinctions;

• very stable foam blankets with very slowfoam drainage times. Medium and highexpansion SYNDET foams can be severelyaffected by wind.

they have the following disadvantages:

• very poor resistance to fuel contamination,often resulting in poor extinction andburnback performance. Medium and highexpansion applications of SYNDET arerelatively gentle and so fuel contaminationis less of a problem;

• very poor sealing around hot objects oftenresulting in poor extinction performances;

• poor burnback resistance;• poor vapour suppression capabilities

at low expansion; vapour suppressioncharacteristics much improved at mediumand high expansion;

• unsuitable for use with polar fuels;• unsuitable for subsurface (base) injection.

(e) AFFF

Low expansion AFFF finished foams tend to havethe following useful characteristics:

• usable foam can be produced with minimalworking, manufacturers suggest that theycan be used primary and secondary aspirat­ed;

• flow quicker than P and FP foams over liq­uid fuel surfaces, quickly reseal breaks in

the foam blanket and flow around obstruc­tions. This often results in very quick fireknockdown and extinction. On some liquidhydrocarbon fuels, these characteristicsmay be enhanced by the film-formingcapabilities of AFFF:

• suitable for subsurface (base) injection;• moderate resistance to fuel contamination

although not as fuel tolerant on non-watermiscible fuels as alcohol resistant foams orFP foams;

and the following disadvantages:

• poor at sealing against hot objects;• poor foam blanket stability and very quick

foam drainage times;

• poor burn back resistance;• poor vapour suppression;• unsuitable for use with polar fuels.

(t) Alcohol Resistant Foam Concentrates(AFFF-AR and FFFP-AR)

Low expansion finished foams produced fromAFFF-AR and FFFP-AR alcohol resistant foamconcentrates tend to have the following usefulcharacteristics:

• suitable for use on fires involving water­miscible liquids such as alcohols and thosepetrol blends that contain high levels ofalcohols and other similar fuel performancelmprovers;

• suitable for use on hydrocarbon liquid fuelfires;

• usable foam can be produced with minimalworking, manufacturers suggest that theycan be used primary and secondary aspirat­ed on non-water miscible fuels. On water­miscible fuels, the foam solutions must notbe applied non-aspirated and also their useon these fuels when secondary aspiratedcannot be recommended;

• flow quicker than P and FP foams overliquid fuel surfaces, quickly reseal breaksin the foam blanket and flow aroundobstructions. This often results in veryquick fire knockdown and extinction.On some liquid hydrocarbon fuels. thesecharacteristics may be enhanced by the

film-forming capabilities of AFFF, film­forming does not occur on water-misciblefuels;

• good resistance to contamination fromhydrocarbon fuels so can be applied force­fully to these if absolutely necessary. Onlygentle application techniques should beused when applying these foams to water­miscible fuels.

• suitable for subsurface (base) injection.They must not be used for base injectioninto water-miscible fuels;

• When used on non-water miscible fuels,control and extinction times are similar tothose of conventional AFFF and FFFPfoams with burnback performance similarto that of FP. Extinction and burnbackperformance is considerably better whenused primary aspirated (i.e. using a foam­making branch) than when used secondaryaspirated (i.e. using a water branch);

• very stable foam blankets with slow foamdrainage times;

• good at sealing against hot metal objects;• good burn back resistance;• good vapour suppression.

and the following disadvantages:

• care is required in selecting the correct rateof induction due to the need to use at 3%concentration for hydrocarbon fuels and at6% for water-miscible fuels. However,some alcohol resistant foams are availablethat may be used at the same induction rate(normally 3%) for both hydrocarbon andwater-miscible fuels.

4.15 Environmental Impact ofFirefighting Foams

4.15.1 General

Firefighting foams are the most effective means ofextinguishing most liquid fuel fires. In doing so.they greatly reduce fire spread, the air pollutionpotential of a fire and the amount of water thatneeds to be used to tackle the fire. This in turnreduces the amount of contaminated water pro­duced during firefighting operations and theenvironmental impact of this run-off.

Firefighting foams can also be of benefit by pre­venting the release of flammable or toxic vapourinto the environment.

The use of foams for firefighting is infrequent andat changing locations. Consequently, the impact onthe environment in these areas does not accumu­late although it can be severe at the time of theincident. In contrast, areas used for training arelikely to be frequently exposed to contaminationby foams and the run-off from these sites should becontrolled by containment and disposal to appro­priate treatment works.

Generally, the environmental effects of foams areconsidered in terms of their toxicity and theirbiodegradability. It should be remembered that it isthe total volume of the foam concentrate that isreleased into the environment that is of concern, itdoes not matter by how much it has been diluted.

4.15.2 Toxicity

The aquatic toxicity of a substance (i.e. how poi­sonous it is to water life) is usually measured interms of its LCso. This is the lethal concentration ofthe substance in water at which 50% of test speci­mens die within a fixed time period under test con­ditions. Generally speaking, the higher the LCsovalue, the less impact the substance will have onaquatic life.

Sometimes, LCIO and even LCo measurements aremade or required. These are much more demand­ing with LCo indicating the concentration at whichthere has been no observable affect to the test spec­imens.

Unfortunately, the range and type of test speci­mens that are tested varies widely as does theirsusceptibility to the effects of the substance.

For most foam concentrates, only the foam manu­facturers' toxicity information is available; veryfew independent tests have been carried out.Toxicity testing can be very expensive to perform.Consequently, some foam manufacturers do notprovide comprehensive values, others provide val­ues for a small or wide range of test specimensincluding algae, water flea (often Daphnia Magna)and fish (often either rainbow trout or fathead

36 Fire Service Manual

...Firefightinf!, Foam - Technical 37

Chapter 5 - Equipment

5.2.1 General

t

Chapter

LX hand-held foam-making branches;LX hand-held hosereel foam unit;LX foam generators;LX foam monitors;MX hand-held foam-making branches;LX and MX hand-held water branch'snap-on' attachments;MX foam pourers:HX foam generators.

5.2 Foam-Making Eq ip

The above equipment is available in various sizesrequiring from less than 50 litres per minute toover 15,000 litres per minute of foam solution.

The primary aspirating foam-making equipmentused by brigades can be divided into the followingmain categories:

Some types of foam-making equipment are fittedwith a means of picking up foam concentrate at theequipment via a length of tube; these are known as'self-inducing'. Some types of these operate atfixed induction rates (e.g. 3% or 6%) while othershave control valves which enable them to bequickly adjusted to pick-up foam concentrate at arange of concentrations. It is also usually possibleto turn off the induction facility completely so thatthe foam-making equipment can be lIsed with pre­mix foam solutions (see below).

••••••••

With all other types of foam-making equipment,the foam concentrate must be introduced into thewater stream at an earlier stage, usually by someform of induction or injection equipment (see thisChapter, Section 5.3), this results in the productionof a 'premix' foam solution. In other word, thefoam concentrate and water have been mixed

Firefighting FoamTech ·ca

5.1 General

• Foam concentrate induction andinjection equipment (e.g. in-line inductorsetc.).

Specialised foam equipment for fighting storagetank fires is not covered here but is described inVolume 2 of the Manual.

The two main types of foam equipment describedhere are:

This Chapter describes some of the foam equip­ment that is currently in use within the UK fire ser­vice. The aim is not to describe every item ofequipment available but to give examples and indi­cations of their performance.

• Foam-making equipment (e.g. foam­making branches, foam-makinggenerators etc.);

Much of the information contained within thisChapter has been obtained from manufacturers.This information should only be used as aguide to performance and may not reflect actu­al performance under operational conditions.Eguipment should always be tested under realisticconditions before purchase to ensure that all oper­ational requirements and performance criteria aremet. In addition, the inductionlinjection and foammaking equipment should be checked at regularintervals, using operational pressure / flow condi­tions and hose lengths, to ensure that the foam­making system is working correctly and thatthe required quality of foam is being produced(see Chapter 4, Section 4.12 and this Chapter,Section 5.5).

centage, the higher the biodegradability of a foam,the quicker the foam is broken down.

The Water Research Council (see above) foundthat in most environmental hazard assessments,high biodegradability is considered desirable.However, it has been found that the main environ­mental impact of the use of foam is the rapiddepletion of oxygen from water due to highbiodegradability. This has the effect of asphyxiat­ing aquatic organisms. They concluded that slow­er (low) biodegradability of foam concentratesmay in fact be more desirable when making futureenvironmental hazard assessments.

They also found that manufacturers only providelimited biodegradability test data which was of lit­tle use in differentiating between the biodegrad­ability of different foam concentrates. From thedata available, there were indications that foamtype was not a good indicator of biodegradationpotential. Five different foam types were of lowbiodegradability, these were SYNDET, P, FP,AFFF and AFFF-AR. However, some AFFF andSYNDET foam concentrates were of highbiodegradability.

None of the data gathered enabled an assessmentto be made of the biodegradability of the fluoro­surr'actants contained in AFFE AFFF-AR, FP,FFFP and FFFP-AR foam concentrates. Thesechemicals may remain (persist) in the environmentfor long periods of time before degrading.Measurements of biodegradability are made by

carrying out two different tests and comparingtheir results.

Biodegradability of a substance is a measure ofhow quickly it is broken down by bacteria.Bacteria in the environment will break down andeat the substance, extracting oxygen from the sur­rounding water as they do so.

minnow). However, it is extremely difficult tocompare the toxic effects of foam concentratesunless the same specimens, test conditions andtoxicity measurement criteria are used.

From the data they collected, some SYNDET foamconcentrates appeared to be the most toxic and allof the protein based foam concentrates were of lowacute toxicity. However, some AFFF and AFFF­AR foam concentrates were also found to be in thislow acute toxicity band.

4.15.3 Biodegradability

A review of firefighting foam concentrates carriedout by the Water Research Council on behalf of theNational Rivers Authority during 1994 (Reference6) concluded that all of the toxicity data they col­lected from various sources, particularly manufac­turers, indicated that none of the foam concentrateswere of high acute toxicity to test specimens. Theyfound that most foam concentrates were tested onwater flea or fish although indications were thattesting on algae would have produced results for amore sensitive species.

One test provides a measure of the ChemicalOxygen Demand (COD). This is the total amountof oxygen required to degrade a set amount offoam; the lower the COD, the less oxygen that isstripped from the environment.

The second test provides a measure of theBiochemical Oxygen Demand (BOO). This is anindication of the foam concentrate's ability to con­sume that amount of oxygen within a specifiedtime period, usually 5 days (referred to as BOOs).

Most of the data issued by foam manufacturersconsists of biodegradability values in terms ofBOOs/COD as a percentage. The higher the per-

38 Fire Service Manual Fire/ighting Foam - Technical 39

• 'tn

(b) LX Foam-making Branch Performance

expansion ratio and very short drainage times. Ifthe outlet is too large, the expansion is higher butthe throw is reduced.

Some branches may also contain flow straighten­ing sections at the nozzle to reduce turbulence atthe outlet of the branch. These assist in forming acoherent 'rope' of finished foam with little fall outof foam along its trajectory. However, these tend toconsiderably reduce the throw of the branch. Forfoam-making branches without flow straighteningsections, considerable amounts of foam can fallout of the stream along their trajectory resulting ina greatly reduced foam volume actually arriving inthe area of impact.

Large scale petrol fire trials have been calTied out(Reference 7) where the firefighting performanceof a short LX foam-making branch (approximatelength 0.5m) and a longer LX foam-makingbranch (approximate length 0.8m) were compared.When these fires were fought with film-formingfoam concentrates, both types of branches

It is generally recognised that the longer the foam­making tube, the better the working and mixing offoam solution with air. This results in a morestable finished foam with drainage times thatare longer than those produced by shorter foam­making branches.

In the diagram are two orifice plates. The upstreamorifice is the larger of the two and its function is tocreate turbulence in the space between the two ori­fice plates so that when the jet issues from thedownstream orifice, it rapidly breaks up into adense spray. The spray fills the nalTOW inlet sec­tion of the foam-making tube and entrains largequantities of air through the air inlet holes. Thedownstream orifice is smaller and is calibrated togive the designed foam solution flow rate at therecommended operating pressure (e.g. 225 Ipm at7 bar branch pressure).

Figure 5.3 Principal features of a Low Expansionfoam branch pipe.

Most foam-making branches have a nalTOW sec­tion at the inlet end in which the air entrainmenttakes place, and then a wider section in which thefoam forms. The wider section of the foam-makingtube sometimes contains 'improvers' (e.g. semi­circular baffles, gauze cones) which are designedto work the foam solution in order to producelonger draining finished foam. The drawback ofusing improvers is that the extra working of thefoam that they cause uses energy from the foamstream resulting in a reduction in the distance thatthe finished foam can be thrown.

At the outlet, the branch is reduced in diameter toincrease the exit velocity, thus helping the finishedfoam to be thrown an effective distance. Thedesign here is crucial; too narrow an outletproduces back pressure which results in less airentrainment and finished foam of very low

equipment, it is the nominal flow requirement onlythat is used to classify them. The use of this classi­fication also aligns with application rates (seeChapter 7) which recommend the minimumamounts of foam solution, in litres per minute, thatshould be applied to each square metre of fire area(Ipm/m2).

For MX and HX foam-making equipment, boththe nominal flow requirement and the volumefoam production are used to classify their output.Generally, the volume foam production figuresspecified by manufacturers will be those achievedwhen using SYNDET foam concentrates.However, film-forming foams may also be used toproduce MX foam and these are likely to give dif­ferent foam volume outputs.

(a) How They Work

5.2.2 LX Hand-held Foam-makingBranches

Figure 5.3 illustrates the principal features of atypical hand-held LX foam-making branch.Designs vary and will incorporate some or all ofthese features. The strainer is frequently omitted,as often is the on/off control.

Figure 5.2 F450 450 litreslmin offoam solutionat 7 BAR. (Photo: Mid and West Wales Fire Service)

Some large output primary and secondary aspirat­ing monitors are described in Volume 2 of theManual. These are primarily meant for applyingfoam to storage tanks. The foam solution supplyrates for these monitors can be in excess of 40,000litres per minute.

Secondary aspirated foam is often produced usingstandard main line and hosereel water branches.However, some purpose designed secondary aspi­rating LX foam-making branches and monitorshave been produced.

together prior to arriving at the foam-makingequipment.

A less often used method of producing a premixfoam solution is by mixing the correct proportionsof water and foam concentrate in a container priorto pumping. Some brigades have used this methodin the water tanks of water tenders.

In general, the means of distinguishing betweenthe capacities of different foam-making equipmentis either by the nominal flow requirement of theequipment (litres per minute, lpm) and/or the vol­ume of the foam produced (cubic metres perminute, m3/min). Usually, for LX foam-making

Figure 5.1 FB5x Mkll 225 litreslminfoam solutionat 5.5 BAR. (Photo: Mid and West Wales Fire Service)

40 Fire Service Manual Firefighting Foam - Technical 41

Flexible bag

line inductor (see below), and the air is drawn inthrough orifices adjacent to the water inlet. Theequipment can only work against limited backpressure, so the length and size of the hosebetween the generator and branch, and the size ofthe branch, need to be carefully selected.

Such generators are used to a limited extent in theFire Service. A typical example has a recommend­ed water inlet pressure of 10.5 bar and a nominalwater requirement is 255 Ipm. It can be used withup to 60 m of 70 mm hose and a water branch witha 38 mm nozzle. Larger sizes of generator aremade but are generally used in fixed installations.

LX Foam Generators

Foam-makingbranchpipe

Figure 5.4 Hand-heldHose reel Foam Unit.

When operated at 3.5 bar with a flow rate of 46Ipm, the manufacturer claims that the unit will pro­duce foam with an expansion of approximately 8.

As an alternative to a foam-making branch, a LXfoam generator may be used. This, when insertedin to a line of hose, induces appropriate amounts offoam concentrate and air into the water stream togenerate finished foam, which is then deliveredthrough the hose to a water-type branch for appli­cation as aspirated foam. The foam concentrate isinduced using the same principle as that of an in-

5.2.4

LX Hand-held Hosereel FoamUnit

adjustable jaws at the outlet giving the option of acohesive jet or a fan like spray. They also have anon/off trigger mechanism controlling the release ofthe foam.

One adjustable jaw type 225 Ipm foam-makingbranch is claimed by the manufacturer to givethrows ranging from 7 metres with the jaws closed(i.e. spray mode) to 13 metres with the jaws open(i.e. jet mode) when operated at 7 bar.

This consists of a p011able hand-held unit, similarto an extinguisher (see Figure 5.4), which cancontain up to 11 litres of foam concentrate. Anappliance hosereel is connected to an adaptor atthe top of the unit and water is supplied at between2 and 10.5 bar.

5.23

A small proportion of the water is diverted to fill acompletely deflated flexible bag within the con­tainer. Inflation of the bag displaces the foam con­centrate via a siphon tube, the concentrate enteringthe main water stream and passing to an integralLX foam-making branch to give a jet of primaryaspirated foam. The unit is controlled via an on/offvalve on the adaptor.

Foam- Foam Flow Expansion 25% drainage timemaking concentrate (Ipm)branch

Short AFFF 225 17.1 Imin 43secs---

Long AFFF 225 15.7 2min 35secs

Short AFFF-AR 225 14.2 3min 15secs

Long AFFF-AR 225 13.4 6min 4 secs

Short FFFP 225 11.9 54secs

Long FFFP 225 13.7 2min 15sec---

Short FP 225 9.8 Imin

Long FP 225 11.6 3min 15sec

Notes to Table 5.J: Measurements taken form References 5 and 7. Syphon tube

produced foams that gave similar knockdown andextinction times but the foam produced by thelonger foam branches had much longer drainagetimes and gave significantly better burnback pro­tection.

Table 5.1: LXfoam-making branches: comparison offoam propertiesof long and short LX foam-making branches

During these same fire tests, it was found that thefirefighting performance of FP foam was extreme­ly poor when used through the short foam-makingbranch but perfectly adequate when used throughthe longer foam-making branch. Details of some ofthe measurements made of the foam produced bythese branches are given in Table 5.1.

LX foam-making branches operating at their rec­ommended pressure (usually either 5.5 or 7 barbranch pressure) with a flow of 225 Ipm areclaimed by the manufacturers to give throw dis­tances varying from 12 metres (coherent rope) to21 metres (no internal baffles etc.). Hand-held LXfoam-making branchpipes are also available withnominal flow requirements of approximately 450Ipm and 900 Ipm at 7 bar branch pressure. Theseare claimed to throw finished foam a few metresfurther than the 225 Ipm branches.

Some foam-making branches are speciallydesigned for use with film-forming foam concen­trates in crash fire situations. These branches have

42 Fire Service Manual Firefighting Foam - Technical 43

b

Gearing for elevationand depression

Stabilising jack

Foam concentrateinlet

MX Hand-held Foam-makingBranches

Firefighting Foam - Technical 45

Medium expansion foam-making branches aregenerally designed to be used with SYNDET foamconcentrates although other types, such as FP,AFFF, AFFF-AR, FFFP and FFFP-AR, may alsobe used. MX foam-making branches will producefoam at expansions usually ranging from 25: I to150: 1. As a result of these higher expansion ratios,

5.2.6

the tanks and the large distance between the mon­itor (possibly positioned on or below a bund wall)and the tanks make the projection of foam into thetanks extremely difficult.

Iy 4300 lpm at 10 bar inlet pressure with a claimedthrow of 60 metres and height of 24 metres.

The throw distances and heights provided by man­ufacturers are often recorded at different monitorelevations and probably in still air conditions socare must be taken when making comparisonsbetween different makes and types. The quoteddistances are likely to be reduced when the moni­tors are used under operational conditions. If at allpossible, before purchase or operational use, thistype of equipment should be operated at potentialrisk sites to ensure that acceptable throws andheights are achieved. This is especially true ofrisks involving storage tanks where the heights of

Figure 5.7 Photograph show­

ing the layout of a typicaltrailer-mounted foam monitor.(Photo: Angus Fire Armour Ltd.)

Figure 5.6 Portable

foam monitor in use.rPholO: West Midlallds Fire

Brigade)

hangars. Similar monitors are fitted to airport foamtenders, often with adjustable jaws which allowthe option of a flat fan-shaped spray.

There are numerous LX foam monitors in usecoming in a wide range of nominal flow and inletpressure requirements. One example has a nominalflow requirement of approximately 1800 Ipm at aninlet pressure of 7 bar and is claimed by the man­ufacturer to have a maximum horizontal range of50 metres and a maximum height of throw of 18metres. Another example operates at approximate-

1..--------610mm---------.l·1

LX Foam Monitors5.2.5

Primary aspirating LX foam monitors are largerversions of foam-making branches which cannotbe hand-held. They may be free-standing andportable, mounted on trailers or mounted on appli­ances. They usually have multiple water connec­tions, and may be self-inducing or used in con­junction with one of the induction methodsdescribed in Section 5.3 below. They can also befound in fixed installations at oil-tanker jetties andrefineries or as oscillating monitors in aircraft

Figure 5.5 Model5A low expansion foam generator.

44 Fire Service Manual

NozzleHead

PremixSolution

FinishedFoam

Firejigh/ing Foam - Technical 47

Gauze :~~~iiffimmMesh

Figure 5.9 Principle of opera/ion of a medium expansion foam branch pipe.

LX and MX Hand-held WaterBranch 'Snap-on' Attachments

MX Foam Pourers

HX Foam Generators

5.2.7

5.2.8

Typical models of MX foam pourers have nominalflow requirements of from 600 lpm to 1800 lpmwhen operated at 2.5 bar inlet pressure. The foamoutputs of these are claimed to be approximately24m3/min and 72 m3/min respectively at theseoperating conditions. This is at an expansion ratioof approximately 40: I.

In addition to the MX hand-held foam-makingbranches, some free-standing MX foam pourersare also available. These are much larger than thehand-held models, have higher flow requirementsand hence produce greater volumes of foam.However, as their name suggests, finished foampours out of them rather than being projected.They have been designed to stand on their integrallegs for the unattended delivery of MX foam intobunded areas, such as those surrounding fuel stor­age tanks. They operate in a similar way to thehand-held MX foam branches described above.

'Snap-on' attachments are available for use withsome hosereel and main line water branches whichenable primary aspirated LX and MX foam to beproduced. Generally, the foam produced by theseattachments is not very well worked making it lessstable (i.e. has much shorter drainage times) andless effective than that produced by purposedesigned primary aspirating foam branches.

High expansion foam generators are designed tobe used with SYNDET foam concentrate only andusually produce finished foams of expansion ratiosof 200: I to 1200: 1.

5.2.9

Air is blown through the generator by a fan, foamsolution is sprayed into the air stream, and this isdirected onto the surface of a fine net screen. Theair blowing through the net wetted with foam solu­tion produces finished foam with a mass of bub­bles of uniform size which, like the MX foampourers, is "poured" rather than being "projected".

Fire Service Manual

MX hand-held branches in use typically havenominal flow requirements ranging from 225 Ipmto 450 lpm with inlet pressures ranging betweenI .5 bar and 8 bar. The expansion ratio of the foamproduced is usually claimed by the manufacturersto be in the region of 65: I with throws rangingfrom 3 to 12 metres. Typical foam output isclaimed to be approximately 13 m3/min for 225lpm branches and approximately 26 m3/min for450 Ipm branches.

the projection distances of MX foam are much lessthan for LX foam, If at all possible, before pur­chase or operational use, this type of equipmentshould be operated to ensure that acceptablethrows are achieved

Figure 5.8 A medium expansion hand-held foam makingbranch. (Ph%: Mid and We.1I Wain Fire Sen'ice)

With MX foam-making branches, an in-lineinductor is generally used to introduce the foamconcentrate as a premix, The branch then diffusesand aerates the stream of foam solution, and pro­jects it through a gauze mesh to produce bubblesof a uniform size.

46

Plan View

Rear View(with fan duct removed)

Turbine shown dotted

AirFlow

Water discharge(female coupling)

Control for shuttingoff water supply todischarge nozzles

By-pass control to bein fUlly open positionto discharge all waterafter passing throughturbine

Foamducting

fIII,

Figure 5.11 A typical

high expansion foam

generator.

production. This results in a higher expansionratio, with the finished foam containing a lowerpercentage of water. It also slightly increases thewater flow to the turbine, speeding up the fan and,consequently, the air flow.

Because the finished foam cannot be projected, itis often fed to the required application pointthrough a large-diameter flexible tube or ducting.It can, however, be used without ducting, e.g.placed on the side of a ship's hold or in the door­way of an enclosure.

The larger HX foam generators are rather bulkyitems of equipment to carry on a first-line appli­ance, so they are usually brought by special vehi­cles when required. However, some lightweightgenerators have been developed that can fit into astandard appliance locker.

One typical large water turbine driven HX foamgenerator weighs 55 kg and is claimed by the man­ufacturer to produce at 7 bar inlet pressure, with anominal flow of 210 lpm and the by-pass closed,135 m3/min of finished foam with an expansionratio of between 500 and 700: 1. At the same inletpressure, but with a nominal flow of 225 lpm andthe by-pass open, the foam output is claimed to be155 m 3/min of finished foam with an expansionratio of between 800 and 1200: 1.

The water turbine driven generators are obviouslymore suited to applications in areas where there isa flammable risk. Most HX foam generators canalso be used as smoke extractors.

• a petrol engine;• an electric motor;• a water turbine which utilises the flowing

foam solution immediately prior to it beingsprayed into the generator.

Figure 5.10 shows, in diagrammatic form, theessential principles of HX foam generators. Somegenerators require a separate in-line inductor butothers are self-inducing and some are capable ofbeing operated either way.

The generator fan may be powered by:

Some water turbine driven generators incorporatea 'by-pass' system. With the by-pass closed, all ofthe foam solution passing through the generator isused both for driving the turbine and for foamproduction. This produces a lower expansion HXfinished foam containing a higher percentage ofwater. To overcome high back pressure, e.g. whenforcing finished foam through long lengths ofducting or up to a height, the by-pass is opened,and some foam solution is thereby diverted to passthrough the turbine to waste, giving less for foam

Figure 5.12 Large HX

foam generator stowedon foam tender (right).

Large plastic bins

(centre) are for

decanting foam.(Phoro: Northern !re/and F/re

Br/Rade)

Figure 5.10 Essential

principles of a High

Expansion Foam

Generator.

FlexibleDucting

FoamSolution

Air

48 Fire Service Manual Firefighting Foam - Technical 49

This Section also includes information on methodsthat can be used to check the concentration of thefoam solution that is produced by foam-makingsystems.

In-line inductors5.3.2

An in-line inductor is placed in a line of deliveryhose, usually not more than 60 metres away fromthe foam-making equipment. This allows thefoam-making equipment to be moved around rela­tively freely without the additional need to movefoam concentrate containers.

• foam concentrates that are too viscousto be picked up at the correct rate by theinduction equipment. Different typesand manufacturers versions of foamconcentrates will be of different viscosity.These will affect the accuracy of theinduction equipment.

• blocked or obstructed orifices within theinduction equipment;

• poorly calibrated induction equipment(Note: the calibration of new inductionequipment should always be checked withthe foam-making equipment and foam con­centrates it is to be used with);

• incorrect inductor for the foam-makingequipment being used or for the requiredconcentration of foam concentrate. (Note:some manufacturers colour code theirinduction and foam-making equipment toassist in identifying matched equipment)

In-line inductors employ the venturi principle toinduce the concentrate into the water stream.(Note: self-inducing foam-making branches alsousually work in this way). Water is fed into theinlet of the inductor generally at a pressure ofaround 10 bar (see Figure 5.14). This passesthrough the smaller diameter nozzle within theinductor to a small induction chamber and then toon the inductor's large diameter outlet via a flowimprover. As the water enters the small nozzle,its velocity increases dramatically causing itspressure to drop (the venturi principle) and thepressure in the induction chamber to fall belowatmospheric pressure. This partial vacuum sucksthe foam concentrate through the pick up tube andinto the low pressure induction chamber.

Problems that may occur include:

• in-line inductors;• round-the-pump proportioners.

For these reasons, foam concentrate is often intro­duced into the water supply line some distanceaway from the foam-making equipment. The typesof induction equipment most commonly used bythe fire service for this purpose are:

• Control and operation of the inductionsystem can be more carefully carried outat a safe distance from the fire.

• Movement of self-inducing foam-makingequipment is restricted due to the need to

be close to a supply of foam concentrate.• Foam concentrate supplies have to be

transported to the foam-making equipment.

Some of the foam-making equipment described inthe previous Section is self-inducing. In otherwords, the foam-making equipment can pick-upand mix foam concentrate with the water supplyprior to producing finished foam. Generally, apick-up tube, of a few metres length, is used toconnect the foam-making equipment to a foamconcentrate container. This method of induction isnot always satisfactory for the following reasons:

tions may be necessary to ensure that these levelsof accuracy are acceptable and will not affect thefirefighting performance of the resulting foam orlead to unacceptable amounts of foam concentratebeing wasted.

Whatever foam induction or injection equipment isused, its operation should be checked regularly toensure that the rate at which the foam concentrateis introduced into the water stream is accurate.Such checks should involve the whole of the foamsystem to be used operationally, including thefoam-making equipment, the foam concentrate,typical hose runs and typical pump/branch operat­ing pressures and flows, to ensure that the systemas a whole works as expected.

• long hose runs producing high backpressures which prevent the inductionequipment proportioning correctly. orat all;

Fif!,ure 5./3 A typical

small water-driven.

high expansion fuam

generator.

for 1% concentrate, induction rate to bebetween 0.9% and 1.1 %;

for 3% concentrate, induction rate to bebetween 2.7% and 3.3%:

for 6% concentrate, induction rate to bebetween 5.4% and 6.6%.

up, a weak foam solution will be formed which islikely to produce a poor blanket of quickly drain­ing foam. If too much foam concentrate is pickedup, a strong foam solution wi II be formed which islikely to produce foam that is too stiff to flow ade­quately across the surface of a fuel probably result­ing in poor firefighting performance. In addition,expensive foam concentrate will be wasted and thepossible overall duration of firefighting will bereduced due to rapid consumption of the availablesupply of foam concentrate.

Typically, variations in the accuracy of induc­tionlinjection equipment of + or - 10% of therequired concentration are usually acceptable andare unlikely to affect firefighting peri"ormance. thatIS:

Other levels of accuracy are often stated in stan­dards and by equipment and foam concentratemanufacturers. Discussions with these organisa-

5.3 Foam Concentrate Inductionand Injection Equipment

5.3.1 General

One typical small water turbine driven HX foamgenerator weighs 16 kg and is claimed by themanufacturer to produce at 7 bar inlet pressure.with a nominal flow of 245 Ipm, 80 m3/min of fin­ished foam with an expansion ratio of 330: I.

Foam concentrate induction and injection equip­ment is used to introduce foam concentrate into thewater supply in order to produce foam solution.There is a need for this equipment to work accu­rately in order to avoid wastage of foam concen­trate and, more importantly, to help to ensure thatthe finished foam is of optimum quality.

The more concentrated a foam concentrate. (e.g. aI % foam concentrate is more concentrated than a3% foam concentrate) the lower the rate of flowthat the foam concentrate is required to be intro­duced in to the water stream. Consequently, espe­cially for I % systems. even slight variations in thefoam concentrate flow can result in much weak­er/stronger foam sol utions being produced thanrequired. If too little foam concentrate is picked

50 Fire Service Manual Firefighting Foam - Technical 51

Figure 5.16 An inline inductor (top) connected to apressurised foam concentrate supply (bollom).

(Phoro: Mid and Wesf Wales!

• for optimum performance, the inductormust be matched to the foam-makingequipment;

• for optimum performance, the inductormust be matched to the type and concentra­tion of foam concentrate in use;

• pressure losses through the inductor inexcess of 30% can be expected at thenormal working pressure range when usingmatched foam-making equipment;

• accuracy of proportioning will vary withpressure.

The disadvantages of in-line inductors are:

• generally the cheapest induction systemavailable;

• simple, robust and with few moving parts;• quick deployment/redeployment on the fire

ground;• foam solution does not pass through the

pump or appliance pipework making cleanup easier and reducing the possible corro­sive effects of the foam solutions.

The advantages of the use of in-line inductors are:

Practically all in-line inductors are designed toinduce the foam concentrate through a pick-uptube placed in a drum or similar container. Theycan, however, also be used in conjunction with apressurised foam concentrate supply (Figure 5. I6).

Figure 5.15 An inline variable inductor.

Fixed and variable rate in-line inductors are avail­able. Fixed rate inductors can only be used at oneinduction rate, generally either 1%,3% or 6%. Theinduction rate of variable in-line inductors canusually be varied anywhere between 1% and 6%by the use of a control knob (Figure 5.15).

Other inductors, without the bypass, will only givethe COlTect induction rate at one particular inletpressure and flow, e.g. at 7 bar and 225 Ipm.Operation other than at the pressure and flows rec­ommended by the manufacture will result in inac­curate foam pick up rates, or no foam pick up atall.

flowrates but from different manufacturers.However, the accuracy of inductors containingbypass valves can vary considerably with pressurealthough they will tend to be slightly more accu­rate at varying pressures than those without bypassvalves (see below).

~ IFoam solution ~

the foam-making equipment with that of the induc­tor. Inline inductors are usually identified by theirnominal flow rate at 7 bar outlet pressure. Typicalsizes of inductor are 225 lpm, 450 lpm and 900Ipm. Consequently, an inductor designed for aflow of 450 lpm can be used with one foam-mak­ing branch requiring 450 lpm or two foam-makingbranches, each requiring 225 lpm, and so on.

It is important to note however, that only oneinductor should be used in anyone hoseline. Forinstance, two 225 lpm inductors must not be usedin a single hoseline to supply a 450 lpm foam­making branch. If this were to happen, the combi­nation of the pressure losses across each of theinductors would result, at best, in the delivery tothe foam-making branch of a very Iow pressureand low flow foam solution of incorrect concen­tration.

Some inductors contain a bypass valve (see Figure5.14) which assists in enabling them to maintaininduction over a range of inductor inlet pressures,often 4 to 10 bar, when using the correct foam­making equipment. In addition, the bypass valvecan help to minimise the pressure drop across theinductor and assist in overcoming some slight mis­match problems caused by using inductors andfoam-making equipment of similar nominal

Hermaphrodite inductioncoupling

Foamconcentrate------

Non-returnball

Maleinstantaneous

inlet

Figure 5.14 Principle of operation of an inline inductor.

A non-return valve (a ball is illustrated for this pur­pose in Figure 5.14) must be included in the foamconcentrate pick up line to prevent water flowingback into the foam concentrate container.

There will always be a pressure drop across theinductor of at least 30% of the inlet pressure. Thisis necessary for the inductor to work properly. Thepressure drop is due partly to turbulence and part­ly to the energy loss involved in the inductionprocess. Pressure drops in excess of 70% havebeen recorded for hosereel in-line inductors (seethis Chapter, Section 5.3.6).

In order for it to operate effectively, it is importantto match the pressure and flow characteristics of

If the back pressure at the outlet of the inductor istoo high, this may result in the pressure dropacross the inductor being less than required. Insuch circumstances, the velocity of the water trav­elling through the inductor nozzle would not behigh enough to enable the pressure in the inductionchamber to fall below atmospheric and so theinductor would fail to work. High back pressurecan be caused by connecting too many lengths ofhose between the outlet of the inductor and thefoam-making equipment or through differences inelevation.

52 Fire Service Manual Firefighting Foam - Technical 53

55Firejiglzting Foam - Technical

container. Pressure control valves are availablewhich can help to reduce this problem (seebelow).

However, one of the major advantages of round­the-pump proportioners is that their use does notresult in pressure losses at the output side of thepump.

Another drawback of this type of equipment is thatthe foam solution has to pass through the pumpcasing. This may cause corrosion problems withinthe pump and other areas of the appliance wherethe foam solution may enter, such as the water tankand pipework. In addition, the orifices within theinductor are extremely small; these can easily beblocked by small pieces of debris or foam concen­trate sludge. Once blocked, the system must betaken apart and the debris removed. For systemsfixed on to appliances, this requires the applianceto be taken off the run.

Foam concentrate inlet

3

100

x Required

percentage

concentration

100

x

Foam

equipment

flow rate

5.81pm

193

Dial

setting

Dial

setting

Round-the-pump systems require the pressure onthe suction side of the pump to be less than one­third of the pressure on the delivery side in orderto function correctly. If this is not the case, thenwater may be forced into the foam concentrate

BOl/om: external view.

Top: cu/(/wa.v view.

Figure 5.18 A typical

round-the-fJUmp

proportioner.

However, each time the flow to the foam-makingequipment changes, then a new setting would haveto be calculated to maintain accurate foam concen­

tration.

Figure 5.17

Diagrammatic layoUlof a round-the-pump

proportioner system

where there is a built­

infoam tank.

Tank topump

/valve

\Suction

inlet

Watertank

Isolating valves can be incorporated to cut off thesystem when foam is not required. Various othervalves in this SOlt of system are incorporated to:

• drain the foam concentrate tank;

• flush the system;• connect a pick-up tube in case a foam

supply other than that contained in theappliance foam concentrate tank needsto be used.

Although this proportioner has an operating pres­sure range of between 3 and 14 bar, the recom­mended pressure is 7 bar, with a water requirementof 193 lpm.

The induction rate for a round-the-pump inductorhas to be selected by a dial calibrated in litres perminute. Consequently, the operator must know theflow rate at which the foam equipment is operatingin order to be able to calculate the correct pick upflow rate for the concentration of foam concentratebeing used. For instance, if the supply to the foam­making equipment is 193 [pm, and 3% concentrateis being used. then the inductor dial should be setas follows:

Water

Foam concentrate

Foam Solution(high concentration)

Foam Solution(working concentration)

+

Variableproportioner

/+

Round-the-pump Proportioners

Fire Service Manual

/'"Drainl

flushing!pickup tube

valve

53.3

This type of inductor is connected across a pumpand can either be a permanent fixture in the appli­ance or, with adapters and connecting hoses, standalone. Two typical available models are one with anominal induction flow range of 0-45 lpm and theother with a nominal induction flow range of 0-90Jpm. The induction flow can be altered withinthese ranges by the use of a rotating grip handle onthe body which has a scale calibrated in litres perminute.

Figure 5.17 shows a typical round-the-pump pro­portioning system where an appliance has a built­in foam concentrate tank. When pumping begins.some water flows to the deliveries and some pass­es to the proportioner. The proportioner inducesfoam concentrate to produce a rich foam solutionwhich passes back to the suction side of the pump.Before re-entering the pump, the foam solutionmixes with a fresh intake of water, and is conse­quently diluted to the required concentration. Mostof it then passes to the deliveries, while a smallamount returns to the proportioner where moreconcentrate is induced. and the sequence isrepeated.

54

57

From hydrant

Firefighting Foam - Technical

IUpstream tapping (

Even at smaller incidents, where it is practicable touse foam concentrate drums, it may be impossibleto determine when the concentrate is about to runout. This could lead to water being discharged ontothe fire. This may also occur whilst the pick-uptube is being transferred when a containerbecomes empty.

Some firefighters adapt foam concentrate con­tainers by cutting off the top so that the contents

Control pressure to control valve

Control valve'balanced'

Ratio of area ofpiston face 5: J

supply. Spillages can also occur and thelogistics of keeping the dams topped upneed to be considered. Debris may alsoenter the dams which may lead to block­ages of the induction system.Since the pick-up system requires the con­centrate container to be positioned verynear to the inductor, it may not be possiblefor a bulk supply to be positioned closeenough to supply the inductor directly.

Figure 5.19 A typical

pressure control valve

with culawav drawing

and schematic diagram.

•

At a large incident requiring perhaps several largefoam monitors. bulk supplies of foam concentratewill be required. In these circumstances, the con­ventional system of inducing the concentrate via apick-up tube may be impractical. for the followingreasons:

If the upstream (i .e. hydrant) pressure increases.the downstream side will experience a proportion­ally greater pressure increase. This will immedi­ately cause the piston to move, closing the butter­fly and reducing the flow through the valve. there­by reducing the downstream pressure until the 5: 1ratio is restored. If the hydrant pressure falls, thereverse process will occur.

Figure 5.19 illustrates a typical pressure controlvalve. Water, under pressure from the hydrant.passes through the valve over a movable butterfly.This butterfly is connected to a hydraulic pistonwhich receives pressure from both sides of the but­tert1y. The area of the piston which is subjected topressure on the upstream side is one-fifth of thearea of the piston on the downstream side, so theforces acting on the piston will balance when thedownstream pressure is one-fifth of the upstreampressure.

To prevent this situation from arising, a pressurecontrol valve may be used with the proportioner.The valve reduces the pressure in the pump inletline to one-fifth of the incoming pressure, thusbringing it within the required limit under most ofthe operational conditions that are likely to beencountered. The valve may be fitted as an integralpart of the pipework system on an appliance, orused as a portable unit inserted into the pump inletline at any convenient position.

(a) General

5.3.5 Pressurised Foam Supply

• It may not be feasible to use foam concen­trate drums to supply the inductor becauseof the frequency with which they wouldhave to be refilled or replaced.

• The use of open-topped portable dams maynot be entirely satisfactory because whenusing some systems the foam concentratetends to aerate and this can interrupt the

Fire Service Manual

The disadvantages are:

53.4 Pressure Control Valves

To summarise. the advantages of round-the-pumpproportioners are:

• relatively inexpensive, although moreexpensive than in-line inductors;

• they can provide a variable, accurateinduction flow rate over a wide range;

• can be used as a fixed or temporary systemon appliances;

• wide operating pressure and flow range;• do not cause the pressure drops in the

delivery hose that are associated with in­line inductors, this allows foam solution tobe supplied through extended lengths ofhose.

• to maintain accurate concentration of foamconcentrate, the operator must continuallycalculate and adjust the foam concentrateflow rate;

• foam solution is passed through the pump.There is concern regarding conosion of thepump and other associated areas; thoroughflushing after use is essential.

• where the pump feeds more than onebranch, there is a need to match the pumpoutput and the concentrate flow to takeaccount of the number of branches in use atanyone time.

• pressure control valves are needed wherewater feed into the suction side of thepump is high (see below)

• there are very small orifices within thesystem which can easily be blocked bydebris or foam concentrate sludge.

A round-the-pump proportioner will only func­tion correctly if the pressure on the suction sideof the pump is less than one-third of the pressureon the delivery side. If this limit is exceeded,when pumping from a hydrant for instance, theback pressure acting on the outlet of the propor­tioner will be sufficient to inhibit the inductionof foam concentrate. In extreme conditions.where no non-return valves are present. watermay feed back into the foam concentrate con­tai ner.

56

59

Pressurisedfoam

concentrate linecarrying 54litres/min

Bulk foam concentrate

Firefighting Foam - Technical

4 x 900 litres/min inline inductors

1 x 1800 Iitres/min foam monitor

4 x 450 litres/min inline inductors

Pressurisedfoam

concentrate linecarrying 54litres/min

Pressurisedfoam

concentrate linecarrying 108

litres/min

Figure 5.21 Diagrammatic layout of an incident requiring large quantities offoam concentrate suppliedjrom a bulk

foam carrier.

pelton wheel in-line foam injection;pre-induction units;direct coupled water pump.

Figure 5.20Diagram showing one900 litrelmin and two450 litrelminfoambranchpipes receivinga pressurised foamconcentrate supplyfrom a foam tankeror foam main.

When pumping foam concentrate to in-line induc­tors in particular, care should be taken to ensurethat the system has been correctly designed for thissituation. This is mainly because these inductorsare calibrated for their normal operating modewhere they create their own small partial vacuumin order to suck up foam concentrate (see thisChapter, Section 5.3.2). However, when foamconcentrate is pumped under pressure directly tothem, this will act in addition to the partial vacuumand will result in foam concentrate being intro­duced into the system at a much higher concentra­tion than required.

Three other methods of feeding foam concentrateunder pressure into hose lines without the use ofin-line inductors are also briefly discussed below,these are:

•••Fire Service Manual

distribution manifold, andmetering device.

can be seen and topping up is made easier.However, this should be done with care because'swarf' produced when cutting off the tops can bepicked up and can cause blockages of the induc­tion system.

Foam solution tobranchpipes

1 x 900 Iitres/min inductorfitted with 27 litres/min

metering valve_......

To overcome all of the above difficulties, manybrigades have developed pressurised foam concen­trate supply systems in which the foam concentrateis pumped from bulk storage containers directly tothe delivery equipment. This is often achieved byutilising the pumping units on foam tenders to con­vey the foam concentrate to the induction device,which may take the form of an in-line inductor ora constant flow valve.

Brigades have their different versions of this sys­tem, but they will all usually include some typeof:

58

••

(b) Distribution Manifold

61

20mmoutlet with

hermaphroditecoupling

Male instantaneousinlet

Firejighling Foam - Technical

(d) Inline Foam Injection (Pelton Wheel)

As mentioned earlier, high pressure losses, inexcess of 30%, can be expected when using in-lineventuri inductors. It is not unusual for this losstogether with hose, monitor and nozzle losses toadd up to a total pressure loss that makes the per­formance of some pieces of foam-making equip­ment ineffective, particularly in terms of throw.

One alternative system is to make use of a peltonwheel driven positive displacement pump whichwill introduce foam, from a storage tank or foamdam, into the delivery hoses through a regulatingvalve. This valve can be adjusted to suit the injec­tion rate required and once set will inject at therequired percentage regardless of pressure fluctua­tions in the delivery hose. The units can be sup­plied with either fixed or adjustable induction ratesto suit the circumstances.

(e) Pre-induction Units

This system employs two induction units. A pre­induction unit is installed near a hydrant and draws

20mm outlet withhermaphrodite coupling

Shut off valves

Figure 5.23 A typical

distribution manifold.

One example of a metering device consists of aflexible ring resting on a tapered seating. At lowpressure the ring is fully expanded, giving themaximum orifice opening. As the pressure rises,the ring is compressed and forced gradually downthe tapered seating, progressively decreasing thesize of the orifice. The combination of increasedpressure and decreased orifice size maintains aconstant flow (Figure 5.24).

In another example (see Figure 5.25). a neoprenediaphragm (shaped like a plug) is located above aprofiled orifice. When subjected to pressure varia­tions between I and 14 bar, this diaphragm flexesonto the orifice, thereby increasing or decreasingthe available orifice area and maintaining a con­stant rate of flow.

These valves may be inserted at the inlet to eachin-line inductor or at some other point in the foamconcentrate delivery line. Several brigades havehad foam-making equipment modified so that thevalve is incorporated within them. It is, of course,essential that a metering device of the correct flowrating for the equipment is used.

Figure 5.22

Pressurised foam

concentrate supplv

being got to work.(PhoTO: Surrey Fire 011(/

l?eJcue Sen'ice)

(c) Metering Devices

be used, a second manifold can be added to thefirst one, either directly or via additional lengths ofhose. The shut-off valves on the manifolds areopened or closed according to the number of in­tine inductors to be supplied.

In order to ensure the optimum output of foam­making equipment, the correct amount of foamconcentrate should be fed to the inductors at alltimes. To ensure this, a metering device, or con­stant flow valve as it is also known, is inserted intothe line. There are many of these types of devicesavailable.

Fire Service Manual

Various designs have been devised by brigades,some incorporating a metering device. Figure 5.23shows a typical distribution manifold which con­sists of a standard male instantaneous couplingleading to a manifold having two controlled outletswith 20 mm hermaphrodite couplings, one on eachside, and a full-bore on/off valve. The manifoldfinally has a standard female instantaneous cou­pling at the other end.

This type of manifold is capable of feeding one ortwo in-line inductors through 20 mm hose, eachline passing up to 70 litres of foam concentrate perminute. If more than two in-line inductors need to

60

CONSTAFLO

MULTI-CONSTFLO

Premix systems involve foam concentrate beingmixed, to the correct concentration, with, forinstance the whole contents of an appliance watertank. A true premix system is ready-mixed in

(b) Premix

The basic principles of operation of these systemsare given below. This is followed by suggestions foran operational requirement for a system to induceadditives into the high pressure hosereels of a first­line appliance. This operational requirement is thenbriefly compared with the typical performance ofsome existing hosereel induction systems.

o

Premix systemsRound-the-pump systemsInjection into pump inletIn-line inductor

(a) General

There are four categories of system most oftenavailable for use by brigades for the induction offoam concentrates into high pressure hosereels(Reference 8). They are:

5.3.6 Hosereel Foam Induction andInjection Systems

••••

Figure 5.25 Principle

of operation of the

'Mobrey constaflo'

valve.

(2) Multiple valve.

(1) Single valve.

Figure 5.24

Principle of operation

of one type of metering

device (Maric valve).

Graph showing the

performance of a 4.5

litre/min Maric valve.

Flexible ringrolls down

tapered seatunder pressure

decreasingorifice givingconstant flow.

trate motor, that are linked via a common shaft.The water motor is connected into the main waterfeed line to the foam-making equipment. As waterpasses through this motor, it turns and drives thefoam concentrate motor which injects foam con­centrate into the water stream discharging from theoutlet of the water pump. The capacities of themotors are carefully chosen so that the correct per­centage of foam concentrate is injected into thewater line. Due to the linkage between the motors,the percentage concentration remains correct overa wide range of flows through the water motor.

Typical portable versions cover various flowranges between 200 and 2000 litres per minute at amaximum pressure of 15 bar. The induction rate isusually either fixed at 3% or is adjustable from 3%to 6%.

Disadvantages of this type of system are that theyare expensive and that they can produce pressuredrops of 25 to 30% of the inlet pressure.

- Controlled flow using 4,5 litres/min "MARlC" valve- Fixed regulator set for 4.5 litres/min at low pressure- ~ Fixed regulator set for 4.5 litres/min at high pressure

13.5

6FLOW 9.0LITRESIMlN 4.5 --=;;;..;....----:~=--=:_::_:_::-=------:~

O 1-2----------------13

3 4 S 6 7 8 9 10 11 12PRES liRE (BAR)

Flexible ringin normalposition

maximwnorifice

By using two stages of induction and making useof the pressure and flow from a separate hydrant, amuch lower pressure loss is experienced across theinductor in the branch. However, the pre-inductionunit must be accurately matched to the foam-mak­ing branch.

concentrate from a reservoir to produce a concen­trate rich solution, generally in the region of onepart water to two parts foam concentrate. This isfed to a specially designed self-inducing foam­making branch. It is at the branch where therequired concentration is achieved.

When using 75mm diameter hose and large moni­tors, the distance from a pre-induction unit to themonitor can be in excess of 750m.

(t) Direct Coupled Water Pump

These usually consist of two positive displacementrotary pumps, a water motor and a foam concen-

62 Fire Service Manual Firefighting Foam - Technical 63

+

(e) In-line Inductors

(c) Round-the-pump

65Firejlghting Foam - Technical

5.5 Methods For Checking FoamSolu ion Concentration asP."oduced by Foam-makingE<luipment

On first inspection. it would appear that the refrac­tometer method is perhaps too difficult to use.However, once some experience has been gainedin its use, the refractometer method will prove

• The use of a refractometer.• Foam concentrate and water flow

measurements

Tests (Reference 9) have shown that a CAFS canthrow foam further than conventional UK fire ser­vice foam-making branches whilst producing awell worked low expansion foam. The system alsoproduced a medium expansion foam with FP thatwas very sticky and could be used to coat vertical

sUlfaces.

5.5.1 General

It is important that the whole foam-making systemis regularly checked to ensure that it works asexpected and that the concentration of the foamsolution produced is as required. The followingtwo methods can be used to check the concentra­

tion of foam solution:

It is claimed by the manufacturers of these systemsthat they have longer throws than conventional fireservice equipment and that they produce betterworked foam with expansion ratios adjustablebetween 7: I and 30: I. When used with class Afoam concentrates, it is claimed that the resultingfoam will stick to vertical surfaces and remainthere for long periods of time. This is said to cooland insulate the material and to prevent the spreadof fire from radiated heat. CAFS may also be usedwith other types of foam concentrates.

pump and an air compressor which combine toproduce an aerated foam at the delivery of thepump. CAFS can be appliance or trailer mountedand can be supplied with a range of water pumps,concentrate injection pumps and different air com­pressors depending on the requirements of the

user.

The system should be capable of continu­ous operation especially while the foamconcentrate supply is replenished.

It should be possible to retrofit the system

to appliances.

The system must work when pumping fromthe appliance water tank, a pressure fedsupply or open water.

The system should not adversely affectbranch performance due to, for instance,

high pressure losses.

concentrate is not required during use thenit should be possible to turn the supply off.No water should flow into the foamconcentrate container at any time.

5.4 Compre sed Air Foam Systems(CAFS)

Compressed Air Foam Systems (CAFS) aredesigned to produce aspirated finished foams with­out the need of a foam-making branch. CAFS con­sist of a water pump, a foam concentrate injection

The outline of the operational requirement givenabove is a good starting point for brigades to eval­uate any new hosereel induction system that may

come on to the market.

It is unlikely that any hosereel induction systemwill meet all aspects of this suggested operationalrequirement. The only system at present that doesnot pass foam solution through the pump is the in­line inductor. However, the use of this results inpressure drops in excess of 70% which wouldadversely affect branch performance.

Systems are often unable to maintain correct ratesof foam proportioning over the range of flows like­ly to be experienced on the fireground. All have tobe operated in very restricted ranges of flow andpressure in order to maintain accurate induction

rates.

In addition to these, the desirability of having foamsolution passing through the appliance pump isalso an important factor to be considered.

•

•

•

•

It should be capable of inducing all typesof foam concentrate at selected concentra­tions within the range I% to 6%. For alco­hol resistant foams, it must be possible toselect 3% concentration for hydrocarbonfires and 6% concentration for alcoholfires.

The accuracy of induction should be main­tained over the varying flow and pressureconditions from one or two hosereels up toa total flowrate of 300 Ipm.

The induction system should be accurate toplus or minus 10% of the correct concen­tration, that is:

for 1% concentrate, induction rate to bebetween 0.9% and 1.1 %;

for 3 % concentrate, induction rate to bebetween 2.7% and 3.3%;

for 6% concentrate, induction rate to bebetween 5.4% and 6.6%.

When foam concentrate is required for thehosereels only, ideally, no foam solutionshould be available from the maindeli veries.

When the hosereels are off, the foamconcentrate flow should be zero. If foam

(t) Suggestions for an OperationalRequirement for a Hosereel InductionSystem

when the recommended jet/spray branch was oper­ated on jet. When the branch was operated onspray, the pressure loss across the inductor was inexcess of 70% and, when the effects of thehosereel tubing were taken in to account. the totalpressure loss was in excess of 90%. Consequently,using this in-line inductor at the appliance pump,connected to the branch with 3 lengths of 19mmhosereel tubing and at a pump pressure of 26 bar,resulted in a branch pressure of less than 3 bar.

The following are suggestions for inclusion in anoperational requirement for a system to induce alltypes of foam concentrates into the high pressurehoseree)s of a first-line appliance:

•

•

•

•

•

Fire Service Manual

A typical round-the-pump system is described ear­lier in this Chapter in Section 5.3. Other similarsystems are available for use in hosereel systems,some of which use flowmeters, valves and micro­processor control. These match the foam concen­trate flow rate to the water flow rate to maintainthe required foam concentration.

(d) Injection in to Pump Inlet

advance of use while a dump tank premix systemdrops foam concentrate into the appliance watertank only when required. For a dump tank system,the whole contents of the tank become a premixand there may be a significant wastage in foamconcentrate if this is not completely used at an inci­dent. Conversely, for a true premix system, theremay be problems in maintaining the correct foamsolution concentration when 'topping-up' the tank.

Injection in to pump inlet systems, as the namesuggests, involves the injection of foam concen­trate in [Q the eye of the pump. Injection is usuallyeither by electric pump or by gravity feed.

Hosereel in-line inductors work in the same way asthe main delivery types previously described inSection 5.3 of this Chapter.

For an electric pump system, a regulator is used tocontrol the amount of foam concentrate that canenter the high pressure side of the pump.Consequently, this can be calibrated to allow vari­ous concentrations of foam concentrate to be usedthrough one or two hosereels (or a main linebranch if necessary). In the gravity fed systems,precisely sized orifices are used to regulate thesupply of foam concentrate into the pump. Severalorifices of different sizes can be included in thesystem. These also allow different concentrationsof foam concentrate to be used or for one or twohosereel branches (or a main branch) to be used inconjunction with the system.

However, tests carried out on one hosereel in-lineinductor (Reference 8) found that there was a pres­sure loss in excess of 50% across the inductor

64

The foam-making system should then be run up toits normal operating conditions. A sample of foam

more accurate and simpler to use than attemptingto measure liquid flows, especially if relativelyaccurate flowmeters are not available.

67Firefighting Foam - Technical

6.71pm

5 x 60

6.7 x 100

225

Induction rate of inductor

3.0%

Flow rate of foam concentrate

45

The following is an example of the use of theabove calculation. A LX foam-making branchoperates, with an in-line inductor, at 225 litres perminute at a branch pressure of 7 bar. The inductorwas timed to pick up 5 litres of foam concentratein 45 seconds.

The induction rate of the inductor is calculated asfollows:

The flow rate through the foam-making equipmentshould, if possible, be measured with a flowmeter.If a flowmeter is not available then the flow rateinformation provided by the manufacturer willhave to be used although this may not be particu­larly accurate for normal fire service operatingconditions.

Flow Method5.5.3

Amount of foam concentrate used (litres) x 60

Time taken to use it (seconds)

Induction rate of inductor (percent)

Flow rate through foam-making equipment (Ipm)

Flow rate of foam concentrate (Ipm)

Flow rate of foam concentrate (Ipm)

solution should be collected from the foam-mak­ing equipment 30 seconds after foam productioncommences. This may mean the collection of foamin a large, clean bucket, with the foam solution thatdrains off being used. The refractive index of thecollected foam solution should then be measuredusing the refractometer and its concentration readoff from the calibration graph.

Different foam concentrate types produce foamsolutions with different refractive indices andrefractometers only cover limited ranges of refrac­tive index. Consequently, care must be taken tochoose the correct refractometer to cover theexpected range of the refractive indices of thefoam solutions to be tested.

Another method of checking the induction rate isto use a wide top container for the foam concen­trate, such as a bucket, with calibrated marks per­haps every five litres. The amount signified byeach mark will depend on the rate of foam con­centrate pick-up expected from the inductionequipment and the size of the container. Ideally,the container should contain the foam concentratethat will be used operationally with the foamequipment. Once the foam equipment has been runup to the required operating conditions, the pickup tube should be inserted into the container. Thetime taken for the level of the concentrate to fallby, for instance, 5, 10, or 15 litres, should then bemeasured. The induction rate can be calculated asfollows:

Refractometer Method

Fire Service Manual

5.5.2

One method of checking the concentration of thefoam solution is by the use of a refractometer.When used for this application, a refractometermeasures the change that occurs in the direction oftravel of light at the junction of foam solution withglass in terms of its refractive index. There is astraight line relationship between refractive indexand solution concentration.

A refractometer looks similar to a small telescopewith an eyepiece at one end and a hinged prismbox at the other. They are available from laborato­ry suppliers and are relatively easy to use withcare. They are widely used in manufacturingindustries for measurements of concentrations offruit juices, battery acids, wines, soft drinks,starches, glues and so on.

The procedure for using a refractometer is as fol­lows; a calibration curve should be produced forthe foam concentrate under test. Ideally, thisshould be produced prior to each occasion that therefractometer is used. It is important that the actu­al foam concentrate that will be passed through thesystem, and water from the same supply, be usedto make up samples of various concentrations offoam solution.

At least 3 calibration points should be chosenwhich cover the range of from 0.5 times to 2 timesthe expected inductor pick-up concentration. Forinstance, for a system supplying 3% concentrate asa 3% foam solution, the calibration samples shouldbe 1.5ml, 3ml and 6ml respectively of 3% foamconcentrate made up and thoroughly mixed withwater each to make 100ml of foam solution (i.e.these would produce 1.5%,3% and 6% foam solu­tion samples). The refractive index of each of theseshould be measured using the refractometer and agraph plotted of refractive index against percent­age concentration. All of the calibration pointsshould then be joined with a straight line.

66

Chapter 6 - Categories of Fire and theuse of Firefighting Foams against them

-

Firefighting FoamTechn·cal

6.1 Ctas. e. of Fire

In the UK the standard classification of fire typesis defined in BS EN 2: 1992 as follows:

Class A: fires involving solid materials, usuallyof an organic nature, in which combus­tion normally takes place with the for­mation of glowing embers.

Class B: fires involving liquids or liquefiablesolids.

Class C: fires involving gases.

Class 0: fires involving metals.

Electrical fires are not included in this system ofclassification (see this Chapter, Section 6.2).

In the following Sections, the general principles ofextinguishment, particularly in relation to fire­fighting foams, are reviewed for each of the' aboveclasses of fire.

6.1.1 Class A fires

Class A fires are those which involve solid materi­als usually of an organic nature such as wood,cloth, paper, rubber and many plastics.

Some manufacturers of AFFF, AFFF-AR, FFFP,FFFP-AR and SYNDET foams state that theirproducts may be used as wetting agents at between0.1 % and 3% concentration to assist in the extinc­tion of class A fires. For these fires, AFFF, AFFF­AR, FFFP and FFFP-AR may be used at low andmedium expansion while SYNDET foams may beused at low, medium or high expansion.

Chapter

There are said to be advantages in the use of wet­ting agents when fires become deep seated. Inthese conditions, water can be slow to penetrate. Awetting agent that reduces the surface tension ofthe water is claimed to greatly improve penetrationto the seat of these types of fire. When a wettingagent is employed, a deep seated fire is predomi­nantly extinguished by the cooling effect of thewater mix rather than by the smothering effect ofany foam that may be produced.

Surfactant based foams display some wettingagent properties, but are more expensive thanproducts sold purely for their wetting agent char­acteristics. From time to time, a few brigades takeadvantage of these wetting agent properties byusing AFFF not only for class B fires (see below),but also, they claim, to make better use of limitedwater supplies on Class A fires. It is claimed thatthe increased cost in agent is often justified byreduced water damage to the property.

Tests have indicated that in some circumstancesthe addition of some foam concentrates to watercan help in reducing the severity of a Class A firewhen compared to the use of water alone(Reference 10). In particular, when applied byspray to wooden crib fires, secondary aspiratedAFFF, and to a slightly lesser extent, FFFP, AFFF­AR and SYNDET, performed significantly betterthan water. Several wetting agents were also testedbut they did not perform much better than water.These results seem to indicate that wetting proper­ties may not alone quickly and effectively dealwith Class A fires involving wood. The smotheringcharacteristics of the foams may also be helping.(In fact, this is the principle under which American'Class A' foams have been developed - seeChapter 2, Section 2.1 .7.)

Firefighting Foam - Technical 69

The use of medium expansion foam against indoorclass A fires, such as in warehouses, could be amore effective and efficient use of foam. It shouldbe possible to restrict the foam application so thatthe area of origin of the fire is kept under observa­tion whilst maintaining sufficient foam flow toforce the foam onto the fire.

Although high expansion foam can be effective,the main practical drawback is that firefighterscannot be sure that the fire has been extinguished.It can be dangerous to enter a deep foam blanket totrack down the seat of a fire since there is a chanceof sudden exposure to heat and products of com­bustion. Under some conditions, the fire can con­tinue to burn for a considerable period at a reducedrate supported by the air released from the foam asit breaks down.

During these tests, because of the size and shape ofthe fires, some areas of the cribs were not ade­quately reached by the spray. Consequently, testswere also performed using jet applications ofwater, primary aspirated AFFF and secondaryaspirated AFFF. There was little difference in thefirefighting performances of these indicating thatif adequate amounts of water can be applied to allareas of a wood fire, it will perform just as well asa primary aspirated or secondary aspirated foamwhen used in the same conditions.

71Firefighting Foam - Technical

Firefighting foams are effective on low flash pointliquids because they trap the vapour at, or justabove, the liquid surface. The trapped vapour thensets up an equilibrium with the liquid which pre­vents further vapour generation. Where deep foamblankets can be formed, such as in storage tankswith a large freeboard, this process may be assist­ed by the increased pressure exerted by the heavierblanket. Film-forming foams produce a thin filmon the sutface of some of these class B liquidswhich may also prevent vapour escaping.

care should be taken to ensure that the fuel doesnot overflow any containment. In addition, wherethe fuel is not contained, the application of waterwill result in further fuel spread.

Lead, as lead tetra-ethyl (or lead tetra-methyl) hasbeen used for more than 60 years to improve theperformance (octane rating) of the hydrocarbonmixtures that constitute petrol. However, since1974, health and environmental concerns haveresulted in the progressive reduction in theamounts of lead in petrol. This reduction of thelead content has led to the use of oxygenates, forexample ethers and alcohols, as alternative octaneimprovers. Oxygenates are only used in eitherleaded or lead-free fuels when the octane ratingcannot be achieved cost effectively by refineryprocesses.

Additional benefits of using firefighting foams onthese liquids are that they cool the liquid sutface,reduce the vapour generation rate, obstruct radia­tion from the flame to the liquid surface andreduce the oxygen level, by the production ofsteam, where the foam, flame and liquid surfacemeet.

Large scale fire tests have been carried out in theUK to establish whether lead-free petrol, conform­ing with current British and European standards,would present any problems to the fire serviceusing their standard low expansion foam equip­ment and techniques (Reference 7). The resultsshowed that providing brigades follow theMinimum Recommended Application Rates givenin this Manual, no problems would be expectedwhen using good quality AFFF or FFFP againstpetrol formulations permitted by current andlikely future standards. However, FP gave poor

(c) Low Flash Point Water-immiscibleClass B Liquids

Water-immiscible liquids with low flash points, orclass A and B petroleum liquids, have flash pointsbelow 21 °C and 55°C respectively. These includeclass A petroleum liquids such as aviation gaso­line, benzene, crude oil, hexane, toluene and petrol(including lead-free), and class B petroleum liq­uids such as avtur jet fuel and white spirit.

The primary mechanisms by which foams extin­guish high flash point liquid fires is by cooling theliquid surface and cutting out back radiation fromthe flames. The smothering action of foam plays arelatively insignificant role.

(b) High Flash Point Water-immiscibleClass B Liquids

Water-immiscible liquids with high flash points, orclass C petroleum liquids, are those with a flashpoint above 55°C such as gas oils, some diesel oils,heavy fuel oils and heavy lubricating oils. At nor­mal ambient temperatures these liquids have lowvapour pressures and so do not generate flamma­ble concentrations of vapour.

Water spray can be used to extinguish fires in highflash point liquids since the cooling effect of wateris sufficient to reduce the generation of vapour tobelow the concentration needed to sustain com­bustion.Firefighting foams are very effective against thistype of fire giving very rapid control and securityagainst reignition, however, use of water spray canbe perfectly satisfactory and far less expensive inmany cases.

Spills or pools of low flash point liquids can pro­duce flammable vapour under normal ambienttemperatures, and flammable or explosive concen­trations can accumulate at low level, since most ofthe vapour will be heavier than air.

Water sprays are unsuccessful in extinguishingfires in low flash point liquids because vapour gen­eration is not sufficiently reduced by the degree ofcooling achieved. However, considerable reduc­tions in flame height and radiation intensity can beachieved with water spray application. Obviously,

The categories are:

6.1.2 Class B Fires

Some high flash point liquid hydrocarbon fires,such as those involving fuel oils, can, under verycontrolled conditions, be extinguished using onlythe cooling effect of water.

Class B fires are those which involve flammableliquids, liquefiable solids, oils, greases, tars, oilbased paints and lacquers (i.e. flammable andcombustible liquids). Combustion of these occursentirely in the vapour that is present above the sur­face of the liquid. For firefighting purposes, ClassB liquids can be subdivided into three categories,each requiring different properties from firefight­ing foams in order to achieve effective and effi­cient fire control and extinction.

(a) General

• high flash point water-immiscibleClass B liquids;

• low flash point water-immiscibleClass B liquids;

• water-miscible Class B liquids.

However, most low flash point hydrocarbon fires,such as those involving petrol, cannot be extin­guished by water alone as the fuel cannot be low­ered to a temperature where the quantity of vapourproduced is too small to sustain burning. In addi­tion, water is generally much denser than liquidhydrocarbons, consequently, when applied duringfirefighting, it immediately sinks below their sur­faces without having any beneficial effect, in fire­fighting terms, on the fire. In fact, the applicationof water may cause the sutface area of the fire toincrease and spread to previously unaffected areas.

Foam is generally applied to both high and lowflash point hydrocarbon fuel fires because it pro­vides a visible blanket which controls and extin­guishes these fires faster and more effectively thanwater.

The three categories of Class B liquids and theirfirefighting characteristics are described in the fol­lowing Sections.

Fire Service Manual

Medium and high expansion foam have beenadvocated for indoor use on class A fires. Theconfinement provided by the walls of buildingsallows the foam to accumulate into a thick blan­ket and also protects the foam from being tornapart by the wind. The mechanism put forwardfor extinguishment is that the foam cuts down themovement of air which supports combustion.There is a cooling effect as water from the foamevaporates, and the steam generated will alsotend to reduce the oxygen level in the air sur­rounding the fire. If the foam blanket is deepenough, it will exert enough downward pressureto enable it to refill holes opened up when thefoam is destroyed by the heat from the fire.Materials and structural members that wouldotherwise be exposed are shielded from heat radi­ation by the foam.

70

Cd) Water-miscible Class B Liquids

Class C fires are those involving gases or liquefiedgases.

extinction performances against lead-free petrolscontaining oxygenates although its burnback per­formances were better than either AFFF or FFFP.

73Firejighling Foam - Technical

Spreading Fires6.3.4

The sustained high levels of heat output maydemand more effort to be made in cooling exposedstructures both to minimise damage during the fireand to prevent reignition after extinguishment. Itshould be remembered that if water is used forcooling, it will break down any existing foam blan­ket in that area. allowing any remaining flames toburn back and preventing further blanket forma­

tion until the water application ceases.

The pool fire, therefore, requires a foam with ahigh fuel tolerance and heat resistance as well asfast flowing characteristics. Adequate post fire

security is also required.

An early step in fighting a spreading fire is tostop the flow of product to the flames wheneverpossible. Water spray provides an excellentscreen behind which to approach the fire andclose leaking valves for instance. The flow froma storage vessel can also be stopped by water dis­placement if there is sufficient freeboard abovethe source of the leak. This method has beensuccessful in the case of a ruptured storage tankline. Water is pumped into the tank to raise theliquid fuel above the level of the outlet line sothat water. instead of product, flows from the

broken line.

Spreading fires can be described as unconfinedspill or pool fires in which the liquid fuel is beingcontinuously supplemented by a spray, jet orstream from a ruptured tank or equipment. Thecontinuous supply of fuel often results in burningliquid flowing into inaccessible areas, such as

drainage systems and floor voids.

burn for a considerable period of time. As a result.firefighters are more likely to encounter a welldeveloped fire burning evenly over a large area,rather than the more isolated, scattered fires whichare characteristic of an unconfined spill. Foammay also be subject to more fuel contamination ifforceful application is used due to the depth of thefuel. Consequently techniques, such as playing thefoam stream against a solid suIface and allowingthe foam'to run onto the fire, may be both desirable

and a practical possibility if suitable surfaces are

available.

Pool Fires

Spill Fires

6.3.3

63.2

The difference between pool fires and spill fires isthat pools may, depending on depth, continue to

Pool fires occur in confined pools of flammable, orcombustible, liquids which are deeper than 250101but not as deep as the contents of storage tanks. Apool fire may cover a large area depending on thevolume of the fuel source and the area of the con­fined space. It may take the form of a bunded areain a tank farm or a hollow pit or trench withinwhich flammable liquid has collected from a rup­

tured process vessel. road or rail tanker.

Spill fires occur in unconfined areas of flammable,or combustible liquids with an average depth ofaround 25mm or less. There is often variation inthe depth of the spill due to unevenness of the sur­face on which the liquid stands. Because it isunconfined, a spill fire may cover a very large

area.

The main characteristic of spill fires is their rela­tively short burning times. If an average burn rateof 40101 of the depth of fuel per minute is assumed,then most of the fuel involved in a spill fire willhave burnt away within 7 minutes of ignition. Suchbrief burn times are, however, unlikely to occur inpractice. Flammable liquid may remain in a rup­tured fuel container and burn for a considerabletime, continuous leakage may replenish the spill ornumerous deep localised burning pools of fuel

may form over a large area.

These descriptions relate to ideal conditions whichin practice are unlikely to occur exactly asdescribed and in some situations, such as incidentsinvolving aircraft. more than one of these situa­tions may occur simultaneously. Even so, they

illustrate the principles involved.

also of particular importance when tackling classB or class C fires. Firefighters often refer to spillfires, pool fires and running fires and the variationsin firefighting technique required to tackle each.This Section describes these types of fire and howtheir characteristics can affect the approach to fire­

fighting.

Class D Fires6.1.4

from a spilled pool of liquid whilst retaining a con­centration above the lower flammability limit.

Low expansion foam is not suitable since itincreases the rate of evaporation from the liquid.For a liquefied gas spillage any reduction in therate of evaporation of the liquid is beneficial inthat it limits the size of the flammable (or explo­sive) cloud generated and hence reduces the possi­bility of ignition.

Medium and high expansion foams are suitable forliquefied gas spills both for fire extinguishmentand vapour suppression. The surface of the foam incontact with the liquid forms an icy slush whichinsulates and protects the upper layers of foam,and which in turn acts by reducing the evaporationrate from the liquid. A further important advantageis the relatively low amount of heat transmitted tothe liquid by water draining from medium andhigh expansion foams.

Class D fires are those which involve combustiblemetals such as magnesium, titanium. zirconium,sodium, potassium and lithium. Firefighting foamsshould not be used with water reactive metals suchas sodium and potassium, nor with other waterreactive chemicals such as triethyl aluminium andphosphorous pentoxide. Other metal fires are treat­ed as class A fires, but in general the use of mediaother than foam or water is found to be more suit­able.

6.2 Electrical Fires

Firefighting foams are unsuitable for use on firesinvolving energised electrical equipment. Otherextinguishing media are available. Fires in de­energised electrical equipment are treated as eitherclass A or B as appropriate (see above).

6.3 ypes of Liquid Fuel Fire

6.3.1 General

The classes of fire discussed in the previousSection have a strong bearing on the tactics andtechniques of using firefighting foam. However,the size, shape and general appearance of a fire is

Class C Fires

Fire Service Manual

6.13

In recent years liquefied flammable gases havebecome an increasingly important source of fuel incommerce and industry. Increased use bringsincreased transportation of these liquids through­out the country by road, rail, and in UK coastalwaters, which in turn increases the possibility ofaccidental spillage. The product group includesLPG (Liquefied Petroleum Gas, usually propaneor butane) liquid ethylene and LNG (LiquefiedNatural Gas, i.e. methane).

Polar solvents and hydrocarbon liquids that aresoluble in water (water-miscible) can dissolve nor­mal firefighting foams. Such liquids include somepetrol/alcohol mixtures (gasohol), methyl andethyl alcohol, acrylonitrile, ethyl acetate, methylethyl ketone, acetone, butyl alcohol, isopropylether, isopropyl alcohol and many others.

Water-miscible class B liquids, such as some polarsolvents, require the use of alcohol resistant typefoam concentrates for firefighting and for vapoursuppression. These foams form a polymer mem­brane between the water-miscible and the foamblanket which virtually stops the destruction of thefoam and allows vapour suppression and coolingto continue. Alcohol resistant foam concentrateslose effectiveness unless they are applied gently tothe sUlface of polar liquids, avoiding plunging.

Boiling points for these liquefied gases are lowand so in the event of spillage, rapid vapour pro­duction occurs. Due to the greater amounts ofvapour produced and the low buoyancy of coldvapour, the dispersal of this vapour is more prob­lematical than from spilled flammable liquids suchas petrol. In still air conditions, and where theground is sloped or channelled, this vapour cantravel long distances from its source. Liquefied gasvapour has been known to travel I ,500 metres

72

This term refers to the case when a burning liquidis moving down a slope on a broad front. The situ­ation is rare but extremely hazardous because ofthe rapidity with which objects and people in thepath of the flow can be enveloped. It is not possi­ble to advise any course of action other than rapidevacuation from the oncoming flow. If monitorsand hoses are immediately available they couldprovide sufficiently rapid knockdown.

On some fuels, film-forming foams are consideredparticularly effective at fast knockdown, althoughother foams can have similarly rapid effects.Another technique is to lay a band of foam at thelower end of the path of flow so that any pool thatbuilds up will do so beneath a foam blanket. Forthis type of application f1uoroprotein or film-form­ing alcohol resistant foams might be consideredmost suitable because of their stability, althoughother foams would also satisfactorily perform thetask.

75

7Chapter

Firefighlinfi Foam - Technical

Fires Involving Water-immiscibleClass B Liquids

Tables 7.1 and 7.2 give the minimum applicationrates of foam solution recommended by the HomeOffice for use by the UK fire service when usingmanual firefighting equipment to apply low andmedium expansion foam to fires involving water­immiscible class B liquids. Also, recommendeddurations of foam application are included in the

tables.

73.2

It should be noted that the figures given in Tables7.1 and 7.2 relate to minimum foam solutionapplication rates and times and assumes that all ofthe finished foam produced from the foam solutionactually reaches the surface of the liquid on fire.These rates should not be considered as beingdefinitive; allowances must be made to compen­sate for losses due to circumstances such as fall outof finished foam from the foam stream, adverse

The Home Office recommended minimum appli­cation rates for use by the UK fire service for firesinvolving water-immiscible class B liquids aregiven in Section 7.3.2 below. Advice is given con­ceming the application rates for fires involvingwater-miscible class B liquids in Section 7.3.4

below.

• variations in the quality of foamconcentrate;

• variations in the quality of finished foamproduced;

• some of the detrimental effects of forcefulappl ication.

The recommended mlDlmum application rate isbased on the critical application rate (see above)with an additional 'safety margin' to help to takeinto account factors such as:

ritical Application Ra e

The critical application rate is the application ratebelow which a fire cannot be ex.tinguished. Whenapplied at below this critical rate, the finishedfoam will be broken down, by both the fuel and theheat of the fire, to such an ex.tent that a completefoam blanket will not be able to form over the sur­

face of the fuel.

7.3 Recommended inimumApplication Rate

73.1 General

The Recommended Minimum Application Rate isthe minimum rate at which foam solution is rec­ommended to be applied to a fire. The rateassumes that all of the foam made from the foamsolution actuall y reaches the surt'ace of the burni ng

fuel.

The following Sections describe the meanings ofthese various terms. The most important of thesefor operational use is Recommended MinimumApplication Rate.

• Critical Application Rate• Recommended Minimum Application Rate

• Optimum Application Rate

• Overkill Rate• Continued Application Rate

7.1 General

7.2

Chapter 7 - Application Rates

The application rate of a foam onto a fire is nor­mally expressed as the amount of foam solution, inlitres per minute, to be applied to every squaremetre of the total area to be covered with foam.The following five terms are often used to describevarious foam application rates and it is importantto know the difference between them. they are:

Firefighti 9 Foam ­Techn·ca

Other Terms

The main method of combating running fires is byprevention. Firefighters must be aware of anypotential for a pool fire to breach or over spill itscontainment. Firefighting efforts should be adjust­ed to reduce such a risk, for example, minimisingthe use of cooling water which could drain into thecontained pool and cause overflowing, monitoringthe integrity of containing bund walls and evacuat­ing in advance any area which could possiblybecome inundated.

63.6

Various other terms are used for different types offire and explosion incident such as BLEVE (seeGlossary of Terms - Firefighting Foams, at therear of this Volume), vapour cloud explosion, gasflare, etc. These have not been covered separatelysince the use of firefighting foam is not directlyinvolved.

Running Fires

Fire Service Manual

63.5

If, on the other hand, the burn back rate of flamesthrough the spray, jet or stream of fuel leakingfrom the container exceeds the rate at which thefuel is coming out of the container, then the dis­charging fuel will also be on fire. It may be neces­sary to use dry powder to extinguish fires in flow­ing jets of liquid or gas in conjunction with foamapplication to the spreading fuel. Water sprays areeffective in reducing the heat output from burningjets although they will break down any foam blan­ket already formed.

If the flammable liquid is a high flash point fuel,the burn back rate of flames through the spray, jetor stream of fuel leaking from the container maybe less than the rate at which the fuel is dischargedfrom the leak. In this situation, the discharging fuelwill not be on fire. Consequently, the fire can beextinguished with a foam blanket or water spray ina similar fashion to a pool fire, the only additionalprecaution being to ensure that the level of fueldoes not rise sufficiently to over spill the contain­ment. Sand bagging, diversion channels andpumping out are all useful techniques to help pre­vent breakdown of containment.

74

Ipm/m 2 litres per minute of foam solution per square metre of burning area of fire

Table 7.1: Home Office Recommended Minimum Application Rates of Foam Solution For theProduction ofLow Expansion Foam For Use on Liquid Hydrocarbon Fuel (Class B) Fires

Table 7.2: Home Office Recommended Minimum Application Rates ofFoam Solution For theProduction ofMedium Expansion Foam For Use on Liquid Hydrocarbon Fuel (Class B) Fires

7.5 Overkill Rate

The optimum application rate is not the rate atwhich the quickest extinction is achieved. Toachieve the quickest extinction time, rates inexcess of the optimum application rate arerequired. However. the small reductions in extinc­tion times achieved by these increased applicationrates are at the cost of large increases in the use ofresources such as water, foam concentrate etc. Forsome applications, such as those involving aircrashes, quick extinction times are of the utmostpriority and can be considered a worthwhile use of

these resources.

There is a limit to how quickly a fire can be extin­guished when using firefighting foam. Once theapplication rate has reached a certain level, higherapplication rates give no improvements in extinc­tion time, they only result in a wastage ofresources. These higher application rates are

known as overkill rates.

The optimum application rate is sometimesreferred to as the most economical rate. It is therate at which the minimum overall quantity offoam solution is needed to extinguish a fire. Thisrate usually lies somewhere between the criticalapplication rate and the recommended minimumapplication rate.

7.4 Optimum Application Rate

On water-miscible liquids, application must besuch that the foam blanket is deli vered gently ontothe liquid surface without submerging the foam oragitating the liquid surface. If some submergenceand agitation is unavoidable, the foam blanket willbe destroyed at a high rate and much higher appli­cation rates and application times will be required.

Typical recommended foam application rates forwater-miscible liquid fires range between 4 and 13litres per minute per square metre. However, it isrecommended that the minimum application timefor a spill of water-miscible fuel should be 15 min­utes and for tanks involving these fuels it shouldbe a minimum of 60 minutes.

Fires Involving Water-miscibleClass B Liquids

73.3

Due to the large number of water-miscible fuels inuse, and the varying firefighting performance ofdifferent foams on each of them, information onthe recommended application rates for a particularwater-miscible risk should be obtained from themanufacturer of the alcohol resistant foam concen­

trate to be used.

Alcohols (e.g. Methanol, Ethanol,Isopropanol)

Ketones (e.g. Acetone, Methyl EthylKetone)

Vinyl AcetateAcrylonitrile

Application rates for water-miscible fuels varyconsiderably depending on the following factors:

• the type of fuel;• the depth of fuel;• the type of foam:• the manufacturer of the foam:• the method of foam application.

Some of the most widely used water-miscible liq­

uids include:

In practice, the recommended minimum applica­tion rates are of great importance in pre-planningthe resources needed for a foam attack. It has adirect bearing on the quantity of concentrate, andwater required, and also should dictate the amountof delivery equipment, i.e. appliances, monitors,branch pipes, proportioners and hoses.

In addition, it is recommended that applicationrates should be reviewed if, after 20-30 minutesapplication, there has been no noticeable reductionin the intensity of the fire.

weather conditions. breakdown of foam due toflames before it reaches the fuel surface, and lossof foam due to the thermal convection currentscaused by the fire. For storage tank fires, theserates need to be increased by up to 60% to account

for foam losses.

\

Spill Tanks TanksFuel FuelFlashpoint Flashpoint>40°C <=40°C

/Bund

15 NR NR

15 45 60

15 45 60

15 45 60

15 45 60

15 45 60

Minimum Application Time(Minutes)

Spill Bund

15 60

15 60

15 60

15 60

15 60

15 60

Minimum Application Time(Minutes)

TanksD>=81m

TanksD>=45mD<81m

NR NR NR

8.0 9.0 10.0

6.5 7.3 8.1

6.5 7.3 8.1

6.5 7.3 8.1

6.5 7.3 8.1

TanksD<45m

<= less than or equal to

>= more than or equal to

Ipm/m 2 litres per minute of foam solution per square metre of burning area of fire

NR Not Recommended for this use

Minimum Application Rate of Foam Solution(lpm/m 2)

Spill/Bund

Minimum Application Rate of Foam Solution(lpm/m 2)

Spill/Bund

< less than

> More than

D Diameter of tank

m metre

Foam Type

Protein 6.5

Fluoroprotein 5

AFFF 4

FFFP 4

AFFF-AR 4

FFFP-AR 4

Notes fo Table 7.1

Fluoroprotein 5.0

Foam Type

SYNDET 6.5

AFFF 4.0------------------

FFFP 4.0---------------

AFFF-AR 4.0

FFFP-AR 4.0

Notes to Table 7.2

76 Fire Service Manual Firefighling Foam - Technical 77

7.6 Continued Application Rate

Various standards quote lower rates for continuedapplication after a fire situation has been extin­guished. These rates should be sufficient to main­tain the integrity of the foam blanket and are oftenaround 50% of the minimum recommended foamapplication rate.

F-refighting FoamTechnical

References

1. CFBAC, JCFR Report 19, Trials ofMedium and High Expansion Foams onPetrol Fires. P L Parsons. 1982.

10. FROG Publication 3/91. AdditivesforHosereel Systems: Trials of Foam onWooden Crib Fires, BP Johnson, 1991.

78 Fire Service Manual

2. SROB Publication 12/90, Chemical Effectsof Additives on Fire Appliances andAssociated Equipment, B P Johnson, 1990.

3. CFBAC,JCFR Report 3LAddirivesforHosereel Systems Trials of Foams on 40m 2

Petrol Fires, J A Foster. 1988.

4. CFBAC, JCFR Report 79, Class AAdditives, K Bosley, 1997.

5. FRDG Publication 2/93. A Comparison ofVarious Foams when used againsr LargeScale Petroleum Fires, BP Johnson, 1993.ISBN 0-86252-949-2

6. Foundation For Water Research, R&ONote 339, A Review of Fire FightingFoams ro Identify Priorities For EQSDevelopment.

7. CFBAC. JCFR Report 49, The Use ofFoam Against Large-Scale Petroleum FiresInvolving Lead-Free Petrol SummaryReport, J A Foster, 1992.

8. CFBAC, JCFR Report 43. Equipment ForThe Induction Of Additives Into Hose ReelSystems, J A Foster, B P Johnson, 1991.ISBN 0-86252-652-3

9. FROG Publication 1/94, A BriefAssessment of a Compressed Air FoamSystem, M 0 Thomas, 1994.ISBN 1-85893-149-5

Firefighting Foam - Technical 79

F-refighting FoamTechnical

Further Reading

Firefighting FoamTechn·cal

Glossary of Terms: Firefighting Foams

(Note: Not all of these terms have been used in this Manual of Firemanshipbut they have been included here for completeness)

1.

2.

3.

4

5

6

7

8

80

CFBAC, JCFR Report 40, Survey ofFirefighting Foams, Associated Equipmentand Tactics [Ewbank Preece Reports] 1990.ISBN 0 82652 556 X

Part I : Firefighting FoamsPart 2 : Tactics and EquipmentPart 3 : Large Tank Fires

Fire Service Manual - Volume 2 - FireService Operations - Petrochemicals.

Fire Service Manual - Volume 2 - FireService Operations - Firefighting Foam.

CFBAC, JCFR Report 46, Additivesfor Hosereel Systems Summary Report,B P Johnson, 1992.

CFBAC, JCFR Report 48, An Assessmentof the Damage to Tank Farms in KuwaitFoLLowing Hostilities and theirImplications for UK Practice SummaryReport, M W Freeman, 1992.

SRDB Publication 9/87, Pilot Study onLow Expansion Foam MakingBranchpipes, B P Johnson, P L Parsons,1987.

SRDB Publication 22/88, Additives forHosereel Systems: Preliminary Trials ofFoam on Small Scale Isopropanol Fires,B P Johnson, 1988.

FRDG Publication 5/91, Additives forHosereel Systems: Trials of Foam On TyreFires, B P Johnson, 1991.

Fire Service Malltlul

9 FRDG Publication 4/94, A Comparison OfVarious Low Expansion Foams When UsedAgainst The Proposed ISO And CENStandard Medium Scale (45M2 )Hydrocarbon Fuel Test Fire, BP Johnson,1994

Accelerated ageing

Acidity

Alcohol resistantfoam concentrates

Alkalinity

Application rate

AFFF concentrate

Aspiration

Aspirated foam

Base injection(Subsurface injection)

Bite

Storage of foam concentrate at high temperatures to indicatelong term storage properties of the foam concentrate at ambienttemperatures.

See pH.

These may be suitable for use on hydrocarbon fuels, andadditionally are resistant to breakdown when applied to thesurface of water-miscible liquid fuels. Some alcohol resistantfoam concentrates may precipitate a polymeric membrane onthe surface of water-miscible liquid fuels.

See pH.

The rate at which a foam solution is applied to a fire.Usually expressed as litres of foam solution per square metre ofthe fire surface area per minute (lpm/m2).

Aqueous film-forming foam. AFFFs are generally based on mix­tures of hydrocarbon and fluorinated surface active agents andhave the ability to form an aqueous film on the surface of somehydrocarbon fuels.

The addition or entrainment of air into foam solution.

Foam that is made when foam solution is passed through purposedesigned foam-making equipment, such as a foam-makingbranch. These mix in air (aspirate) and then agitate the mixturesufficiently to produce finished foam. (see also primary aspiratedfoam and secondary aspirated foam).

The introduction of fuel-tolerant primary aspirated finished foambeneath the surface of certain flammable and combustiblehydrocarbons, to effect fire extinguishment. Usually used forthe protection of fixed roof hydrocarbon fuel storage tanks.

The formation of an initial area of foam blanket on the surface ofa burning liquid fuel.

Firefighling Foom - Technical 81

Boiling liquidexpanding vapourexplosion (BLEVE)

Boil-over

Bund area (Dike area)

Branch

Burnback resistance

Candling

The catastrophic failure of a tank containing pressure liquefiedgas (PLG) due to mechanical damage or adverse heat exposurewill result in a BLEVE. A BLEVE will produce blast andprojectile hazards. If the contents of the tank are toxic, then

health and exposure hazards may occur. If the contents areflammable, then a fireball may occur with associated thermalradiation and fire engulfment hazards.

Violent ejection of flammable liquid from its container, caused

by vaporisation of a water layer beneath the body of the liquid. Itwill generally only occur after a lengthy burning period in wide

flashpoint range products, such as crude oil. The water layer mayalready have been in the container before the fire began or may

be the result of the inadvertent application of water (perhaps dur­

ing cooling of the container walls), or from the drainage of foamsolution from finished foam applied to the fire. (see also froth­over and slop-over).

An area sUITounding a storage tank which is designed to containthe liquid product in the event of a tank rupture.

A hand-held foam maker and nozzle.

The ability of a foam blanket to resist direct flame andheat impingement.

Refers to the thin intermittent flames that can move over the

surface of a foam blanket even after the main liquid fuel fire hasbeen exti nguished.

Concentration

Critical applicationrate

Crude oil

Density

Dike area

To achieve effective performance, foam concentrates must bemixed to the concentration recommended by the manufacturer.For each 100 litres of the required foam solution, the foam

concentrate must be mixed as follows:

Recommended Volume of Foam VOlume of Volume ofConcentration Concentrate Water Foam Solution

(litres) (litres) (litres)

1% 99 100

3% 3 97 100

6% 6 94 100

The foam application rate below which a fire cannot be

extinguished.

Petroleum, in its natural state, as extracted from the earth.

Consequently, there are many different types of crude oil. eachwith different characteristics and each yielding different quality

products. The various constituents ensure that crude oils general­ly have wide ranging flash points with usually sufficient fractions

(or light ends) to classify them as class A petroleum products.

The mass per unit volume of a material:

. massDenSity = I

vo ume

See Bund area.

In the UK the standard classification of fire types is definedin BS EN 2: 1992 as follows:

A finished foam produced by mixing two or more chemicals.

The bubbles are typically caused by carbon dioxide released bythe reaction.

'Class A: fires involving solid materials, usually of an

organic nature, in which combustion normally takes placewith the formation of glowing embers.

Chemical foam

Classes of Fire

Class B:

Class C:

Class 0:

fires involving liquids or liquefiable solids.

fires involving gases.

fires involving metals.'

Discharge rate(high expansion foam)

Drainage time

Expansion ratio

The discharge rate of a high expansion foam generator measuredin cubic metres/min (m3/min) of foam at a stated expansion ratio.

The time taken for a percentage of the liquid content of afinished foam sample of a stated depth to drain out of the foam.

For low expansion foam, times taken for 25% of the foamsolution to drain out are usually given; for medium and highexpansion foams 50% drainage times are usually given.

The ratio of the total volume of finished foam to the volume of

foam solution used to produce it:

Expansion ratio =volume of finished foamvolume of foam solution used to produce it

FFFP foam concentrates Film-forming fluoroprotein. These are tluoroprotein foamconcentrates which have the ability to form an aqueous film on

the surface of some hydrocarbon fuels.

Cloud point

Combustible liquid

Electrical fires are not included in this system of classi fication.

The lowest temperature at which a liquid remains clear.

Usually only applicable to high expansion foam concentrates.

Any liquid having a flashpoint at or above 37.8°C (I OO"F).

Film-forming A finished foam, foam solution or foam concentrate that forms a

spreading, thin, aqueous film on the surface of some hydrocarbon

liquids.

82 Fire Service Manual Firejighling Foam - Technical 83

Flow requirement (Iow The nominal supply rate of foam solution required by a foamand medium expansion) branch, measured in litres per minute.

Finished foam

Flammable liquid

Flashback

Flashpoint

Fluoroprotein (FP)foam concentrate

Foam

Foam concentrate

Foam, dry

Foam generator(high expansion)

Foam generator(Iow expansion)

Foam-making branch(foam-makingbranchpipe, FMB)

Foam monitor

Foam solution

Foam, wet

The foam as applied to the fire. It will consist of a mixture offoam solution that has been mixed with air. The foam may beprimary aspirated or secondary aspirated.

Any liquid having a flashpoint below 37.8°C (lOO°F).

The re-ignition of a flammable liquid caused by the exposure ofits vapour to a source of ignition such as a hot metal surface or aspark.

The lowest temperature at which a flame can propagate in thevapour above a liquid.

A hydrolysed protein based foam concentrate with addedfluorinated surface active agents.

The result of mixing foam concentrates, water and air to producebubbles.

The foam as supplied by the manufacturer in liquid form; this issometimes referred to as 'foam compound'. 'foam liquid' or bytrade or brand names.

Foam with a long drainage time, i.e. the liquid content of thefoam takes a long period of time to drain out of the foam; thefoam is very stable.

A mechanical device in which foam solution is sprayed onto anet screen through which air is being forced by a fan.

Similar to a foam-making branch, but inserted in a line of hoseso that the finished foam passes along the hose to a dischargenozzle.

The equipment by which the foam solution is normally mixedwith air and delivered to the fire as a finished foam.

A larger version of a foam-making branch which cannot behand-held.

A well mixed solution of foam concentrate in water at theappropriate concentration.

Foam with a short drainage time. i.e. the liquid content of thefoam takes a sholt period of time to drain out of the foam; thefoam breaks down quickly.

Freeze point

Froth-over

Hazmat

Heat resistance

High expansionfoam (HX)

Hydrocarbon fuel

Induction

Inductor (Eductor)

Induction rate(pick-up rate)

Inline inductor

Knockdown

Low expansionfoam (LX)

Mechanical foam

Medium expansionfoam (MX)

Minimum usetemperature

Monitor

The highest temperature at which a material can exist as a solid.

Overflow of a non-burning flammable liquid from a containerdue to the thermal expansion of the liquid or violent boilingon top of and within the upper layers of the liquid due to thepresence of small quantities of water. (see also boil-over andslop-over)

A proprietary trade name used to describe special types of foamwhich can be used to suppress the vapour production of certainhazardous materials (toxic, odorous and/or flammable).

The ability of a foam blanket to withstand the effects of exposureto heat.

Finished foam of expansion ratio greater than 200: I

Fuels based exclusively on chains or rings of linked hydrogen andcarbon atoms. Hydrocarbon fuels are not miscible with water.

The entrainment of foam concentrate into the water stream.

A device used to introduce foam concentrate into a water line.

The percentage at which foam concentrate is proportioned in towater by an inductor in order to produce a foam solution.Normally this is 1%,3% or 6%.

An inductor inserted in to a hose line in order to induce foamconcentrate prior to the water reaching the foam-making branch.

The ability of a foam to quickly control flames. Knockdown doesnot necessarily mean extinguishment.

Finished foam of expansion ratio of less than or equal to 20: I .

Foam produced by a physical agitation of a mixture of water,foam concentrate and air.

Finished foam of expansion ratio greater than 20: I. but less thanor equal to 200: I.

The lowest temperature at which the foam concentrate can beused at the correct concentration through conventional equipmentsuch as inline inductors and other proportioning devices.

A large throughput branch (water or foam-making) which isnormally mounted on a vehicle, trailer or on a fixed or portablepedestal.

84 Fire Service Manual Firejighling Foam - Technical 85

Multipurpose foamconcentrates

Newtonian liquids

Non-aspirated(Unaspirated)

Non-Newtonianpseudo-plasticliquids

Oleophobic

Over-the-top foamapplication

pH (Acidity/Alkalinity)

Polar solvent

Pour point

Another name given to alcohol resistant foam concentrates.

The viscosity of Newtonian liquids remains the same no matterhow quickly or slowly they are flowing (see also non-Newtonianpseudo-plastic liquids). Most non-alcohol resistant foamconcentrates (such as AFFF, FFFP, FP, P and SYNDET) areNewtonian liquids.

The application, by any appropriate means, of a firefightingliquid that does not mix the liquid with air to produce foam(i .e. aspiration does not occur). The term' non-aspirated foam' isoften used incorrectly to describe the product of a foam solutionthat has been passed through equipment that has not beenspecifically designed to produce foam, such as a water branch.However, the use of this type of equipment will often result insome aspiration of a foam solution. This is because air is usuallyentrained into a jet or spray of foam solution as it leaves thebranch, as it travels through the air due to the turbulenceproduced by the stream and/or when it strikes an object. Thiscauses further turbulence and air mixing. There is sufficient airentrained by these processes to produce a foam of very lowexpansion (often with an expansion ratio of less than 5: I).Consequently, the term secondary aspirated foam is prefelTed inthese cases (see also primary aspirated and secondary aspiratedfoam).

As the rate of flow of non-Newtonian pseudo-plastic liquidsincreases, their viscosity decreases and so they flow more easily.Consequently, getting them to flow initially can be difficult, butonce flowing, their viscosity reduces to a more acceptable level.Many alcohol resistant foam concentrates (such as AFFF-AR andFFFP-AR) are considered to be non-Newtonian pseudo-plasticliquids.

Oil repellent.

The application of foam by projecting it over the sides of astorage tank and directly on to the surface of the contained fuel.

Measurement of the acidity to alkalinity of a liquid on a scale of1 to 14. A pH of 7 is neutral (like that of pure water), a pH of 1 isvery acidic, a pH of 14 is very alkaline.

This term is generally used to describe any liquid which destroysstandard foams, although it actually refers to liquids whose mole­cules possess a permanent dielectric discharge e.g. Alcohols,ketones. Most polar solvents are water-miscible.

The lowest temperature at which a foam concentrate is fluid enoughto pour. This is generally a few degrees above its freezing point.

Preburn time

Premix solution

Primary aspiratedfoam

Proportioner

Protein (P) foamconcentrate

Relative density

Secondary aspiratedfoam

Security

Shear strength

Slop-over

SOlution transit time

Specific gravity

The time between ignition of a fire and the commencement of

foam application.

A mixture in correct proportions of a foam concentrate and water.Use of this term generally implies that the foam is stored in apremix form, as in a portable foam fire extinguisher or as foamsolution in a fire appliance water tank.

Finished foam produced from foam solutions that are passedthrough purpose designed foam-making equipment.(See secondary aspirated foam).

A device where foam concentrate and water are mixed to form a

foam solution.

Protein foam concentrate contains organic concentrates derivedfrom natural vegetable or animal sources. Hydrolysed products ofprotein provide exceptionally stable and heat resistant propertiesto foams although they lack fuel tolerance and have slow knock­

down performance.

see Specific gravity

Finished foams that are produced from foam solutions that areapplied other than by purpose designed foam-making equipment,usually standard water devices. (See primary aspirated foam).

The ability of a foam to seal around hot objects and prevent

reignition.

The measurement of the stiffness of a finished foam samplewhen measured with a foam viscometer. Units of measurement

are Newtons per square metre (n/m2).

When some burning liquids, such as heavy fuel oils or crude oils,become extremely hot, any applied water may begin to boil oncontact with the fuel, the resulting rapid expansion as it convertsto steam may cause burning fuel to overflow its containment andthe fire to spread (see also boil-over and froth-over).

The time taken for foam solution to pass from the point wherefoam concentrate is introduced in to the water stream to when

finished foam is produced.

The specific gravity of a material is a measure of the density ofthe material in relation to the density of water. The specific

gravity is calculated as:-

Specific Gravity = Density of materialDensity of water

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Water-immiscible liquid A liquid that is not soluble in water.

Spill fire

Stability

Subsurface injection

Surface active agents

Synthetic detergent(SYNDET) foamconcentrate

Venturi

Viscosity

A liquid with a specific gravity of less than one will tloat onwater (unless it is water-miscible); a specific gravity of morethan one indicates that water will float on top of the liquid.

A flammable liquid fire having an average depth of not morethan 25mm.

The ability of a finished foam to retain shape and form particu­larly in the presence of heat, flame and/or other liquids. The 25%drainage time is often used as a measure for stability.

See base injection.

A chemical ingredient of some foam concentrates. Finishedfoams is stabilised by the addition of SUlface active agents (orsurfactants) which promote air/water stability by reducing theliquids surface tension. Most surface active agents are organicin nature and common examples are soaps and detergents.

These are based upon mixtures of hydrocarbon surface activeagents and may contain fluorinated surface active agents withadditional stabilisers. They are multipurpose foams in that theycan be used at low, medium and high expansion.

A constricted portion of a pipe or tube which will increase watervelocity, thus momentarily reducing its pressure. It is in thisreduced pressure that foam concentrate is introduced. Thepressure difference across the venturi can be used to force foamconcentrate into the water.

This is a measure of how well a liquid will flow. Liquids aregenerally classed as either being non-Newtonian or Newtonian.A low viscosity is often desirable because it improves the flowcharacteristics of a foam concentrate through pick-up tubes,pipework and induction equipment.

Viscosity will also vary with foam concentrate type and withconcentration. AFFF foam concentrates at 3% and 6%oncentrations tend to be the least viscous, closely followed byP, FP and FFFP foam concentrates at 6%. AFFF at 1% andSYNDET foams, P, FP and FFFP foam concentrates at 3%concentration are appreciably more viscous than these. Thealcohol resistant foams are often the most viscous althoughrecent developments have dramatically reduced the viscosityof some products.

In addition, the viscosity of all foam concentrates will varywith temperature and may be affected by the age of the foamconcentrate. Manufacturers often state the viscosity of theirproducts when measured at 20°C; lower temperatures will resultin higher viscosity.

Water-miscible liquid

Wetting agent

A liquid that is soluble in water. Polar solvents and hydrocarbonliquids that are water-miscible can dissolve normal firefightingfoams (see also alcohol resistant foam concentrates).

A chemical compound which, when added to water in correctproportions, materially reduces its surface tension, increases itspenetrating and spreading abilities and may also provide foaming

characteristics.

88 Fire Service ManualFireflghting Foam - Technical 89