Essentials of Fire Fighting , 5 th Edition

Essentials of Fire Fighting, 5th Edition

Chapter 14 — Fire Streams

Firefighter II

Firefighter II14–2

Chapter 14 Lesson Goal

• After completing this lesson, the student shall be able to effectively apply fire fighting foam using various foam types, concentrates, and delivery devices following the policies and procedures set forth by the authority having jurisdiction (AHJ).


Specific Objectives

1.Describe the suppression characteristics of fire fighting foam. 2.Define terms associated with types of foam and the foam-making process. 3.Discuss how foam is generated.

(Continued)


Specific Objectives

4.Discuss foam concentrates. 5.Describe methods by which foam may be proportioned. 6.Discuss foam proportioners.7.Discuss foam delivery devices.

(Continued)


Specific Objectives

8.List reasons for failure to generate foam or for generating poor-quality foam. 9.Describe foam application techniques.

(Continued)


Specific Objectives

10.Discuss hazards associated with foam concentrates. 11. Place a foam line in service — In-line eductor. (Skill Sheet 14-II-1)


Ways Fire Fighting Foam Extinguishes/Prevents Fire

• Separating• Cooling• Smothering• Penetrating


Terms Associated With Foam

• Foam concentrate• Foam proportioner• Foam solution• Foam (finished foam)


How Foam is Generated

• Foams used today are of mechanical type and before use must be– Proportioned– Aerated

(Continued)



• Elements needed to produce fire fighting foam

(Continued)

– Foam concentrate– Water

– Air– Mechanical

agitation



• All elements must be present and blended in correct ratios

• Aeration produces foam bubbles to form effective foam blanket


Foam Expansion

• The increase in volume of foam when aerated

• Method of aerating results in varying degrees of expansion

• Types of foam


Foam Concentrates — General Considerations

• Foam concentrates must match fuel to which applied

• Class A foams not designed to extinguish Class B fires

• Class B foams designed solely for hydrocarbon fires will not extinguish polar solvent fires


Class A Foam

• Increasingly used in both wildland and structural fire fighting

• Special formulation of hydrocarbon surfactants

(Continued)


Class A Foam

• Aerated Class A foam coats, insulates fuels, preventing pyrolysis and ignition

• May be used with variety of nozzles


Class B Foam

• Used to prevent ignition of or extinguish fires involving flammable and combustible liquids

• Used to suppress vapors from unignited spills of these liquids

• Several types of Class B foam concentrates available

(Continued)


Class B Foam

• Manufactured from synthetic or protein base

• May be proportioned into the fire stream through fixed system, apparatus-mounted system, or by portable foam proportioning equipment

(Continued)


Class B Foam

• Foams such as AFFF and FFFP foam may be applied with standard fog nozzles or air-aspirating foam nozzles

• Rate of application depends on several factors

(Continued)


Class B Foam

• Unignited spills do not require same application rates as ignited spills

• To be most effective, blanket of foam 4 inches (100 mm) thick should be applied to fuel surface


Specific Application Foams

• Numerous types of foam available for specific applications

• Properties of foams vary


Proportioning

• Mixing of water with foam concentrate to form foam solution

• Most concentrates can be mixed with fresh/salt water (Continued)


Proportioning

• For maximum effectiveness, foam concentrates must be proportioned at designated percentage

• Most fire fighting foams intended to be mixed with 94 to 99.9 percent water


Proportioning Methods

• Induction• Injection• Batch-mixing• Premixing


Foam Proportioners — General Considerations

• May be portable or apparatus-mounted

• Operate by one of two basic principles


Portable Foam Proportioners

• Simplest, most common form of proportioning devices

• In-line foam eductors• Foam nozzle eductors


Apparatus-Mounted Proportioners

• Mounted on structural, industrial, wildland, and aircraft rescue and fire fighting apparatus, as well as on fire boats

• Three types


Compressed-Air Foam Systems (CAFS)

• Newer structural engines are equipped with CAFS

(Continued)



• Standard centrifugal pump supplies water, direct-injection foam-proportioning system mixes foam solution with water on discharge side of pump, onboard air compressor adds air to mix before discharging from engine

(Continued)



• Unlike other systems, hoseline contains finished foam

• Advantages• Disadvantages


Handline Nozzles

• Solid-bore nozzles• Fog nozzles• Air-aspirating foam nozzles


Medium- and High-Expansion Foam Generating Devices

• Produce foam that is semistable with high air content

• Medium-expansion foam• High-expansion foam• Water-aspirating type nozzle• Mechanical blower generator


Reasons for Poor-Quality Foam/Failure to Generate Foam

• Eductor, nozzle flow ratings do not match so foam concentrate cannot induct into fire stream

• Air leaks at fittings cause loss of suction

• Improper cleaning of proportioning equipment causes clogged foam passages (Continued)



• Nozzle not fully open, restricting water flow

• Hose lay on discharge side of eductor is too long

• Hose is kinked and stops flow

(Continued)



• Nozzle is too far above eductor• Mixing different types of foam

concentrate in same tank results in mixture too viscous to pass through eductor


Roll-On Foam Application Method

• Directs foam stream on ground near front edge of burning liquid spill

• Foam rolls across surface of fuel (Continued)


Roll-On Foam Application Method

• Firefighters continue to apply foam until spreads across entire surface of fuel and fire extinguished

• Used only on pool of liquid fuel on open ground


Bank-Down Foam Application Method

• May be employed when elevated object is near/within area of burning pool of liquid or unignited liquid spill

• Object may be wall, tank shell, similar vertical structure (Continued)


Bank-Down Foam Application Method

• Foam stream directed onto object, allowing foam to run down onto surface of fuel

• Used primarily in dike fires, fires involving spills around damaged/overturned transport vehicles


Rain-Down Foam Application Method

• Used when other two methods not feasible because of size of spill area or lack of object from which to bank foam (Continued)


Rain-Down Foam Application Method

• Primary manual application technique on aboveground storage tank fires

• Directs stream into air above fire/spill, allows foam to float gently down onto surface of fuel


Foam Hazards to Humans

• Foam concentrates pose minimal health risks to humans

• May be mildly irritating to skin, eyes

(Continued)


Foam Hazards to Humans

• Affected areas should be flushed with water

• Some concentrates, vapors may be harmful if ingested/inhaled

• Consult MSDS for specific information


Foam Hazards to Equipment

• Most Class A, Class B foam concentrates are mildly corrosive

• Follow proper flushing procedures to prevent damage


Foam Hazards to Environment

• Primary impact is effect of finished foam after application to fire/liquid spill

• Biodegradability of foam determined by rate at which environmental bacteria cause decomposition

(Continued)



• Environmental impact of foam concentrates varies

• In the U.S., Class A foams should be approved by USDA Forest Service

(Continued)



• Chemical properties of Class B foams and environmental impact vary on type and manufacturer

• Protein-based foams safer for environment

(Continued)


Summary

• Firefighters must know the differences between the classes of foam, how to generate foam, and how to apply foam most effectively


Review Questions

1.What are the ways that fire fighting foam extinguishes and/or prevents fire?2.Describe types of foam concentrates.3.What are the methods by which foam may be proportioned?

(Continued)


Review Questions

4. What are the types of portable foam proportioners and how do they work? 5.Describe the techniques used to apply foam.

Documents

Essentials of Fire Fighting , 5 th Edition