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BRITISH STANDARD BS 476-3:1975

Fire tests on buildingmaterials and

structures

Part 3: External fire exposure roof test

UDC 614.841.322:620.1:699.81:69.024

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This British Standard, havingbeen approved by the PetroleumEquipment Industry StandardsCommittee, was published underthe authority of the ExecutiveBoard on28 November 1975

BSI 01-1999

First published, June 1952First revision, March 1960Second revision, November 1975

The following BSI referencesrelate to the work on this

standard:Committee reference PEE/1Draft for comment 74/74150 DC

ISBN 0 580 08817 0

Co-operating organizations

The Petroleum Equipment Industry Standards Committee, under whosesupervision this British Standard was prepared, consists of representativesfrom the following Government department and scientific and industrial

organization:

British Gas Corporation

British Mechanical Engineering Confederation

British Rubber Manufacturers Association Ltd.

British Steel industry*

Council of British Manufacturers of Petroleum Equipment*

Department of Energy

Oil Companies Materials Association*

The Industrial organization marked with an asterisk in the above list, together

with the following, were directly represented on the Committee entrusted withthe preparation of this standard:

Association of Hydraulic Equipment Manufacturers

British Chemical Engineering Contractors Association

British Industrial Measuring and Control Apparatus ManufacturersAssociation

British Plastics Federation

British Ship Research Association

British Valve Manufacturers Association

Engineering Equipment Users Association

Steel Castings Association

Amendments issued since publication

Amd. No. Date of issue Comments

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Contents

Page

Co-operating organizations Inside front cover

General foreword iiForeword iii

1 Scope 1

2 References 1

3 Definitions 1

4 Test specimen 1

5 Test equipment 1

6 Test procedure 4

7 Expression of results 5

8 Test report 5

Appendix A Copper asbestos disc radiometer 6

Figure 1 Diagram showing radiation intensities at nine positionson plan of specimen for calibration 2

Figure 2 Typical roof test apparatus 3

Figure 3 Path of travel of pilot flame 5

Publication referred to Inside back cover



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General foreword

BS 476 was published as a single volume in 1932. A later revision expanded thestandard into three Parts:

Part 1:1953, Fire tests on building materials and structures;Part 2:1955, Flammability test for thin flexible materials;

Part 3:1958, External fire exposure roof tests.

In the present revision the three sections of Part 1:1953 have been revised andpublished as new and separate Parts in the BS 476 series. Thus the three sectionsof Part 1 are replaced respectively by:

Part 4:1970, Non-combustibility test for materials;

Part 7:1971, Surface spread of flame tests for materials;

Part 8:1972, Test methods and criteria for the fire resistance of elements ofbuilding construction.

In addition, during the present revision new Parts have been added to the series

as follows:Part 5:1968, Ignitability test for materials;

Part 6:1968, Fire propagation test for materials.

Part 2:1955 has been withdrawn and replaced by BS 2782 Methods of testingplastics, Part 5 Miscellaneous methods.

This British Standard replaces Part 3:1958 which is withdrawn.

At present the BS 476 series comprises Parts 3 to 8 inclusive; other tests are,however, under consideration. DD 36 Fire tests on building materials andstructures: measurement of the optical density of smoke produced by smallspecimens of materials has been published as a Draft for Development. This testwas originally prepared with the intention of issuing it as BS 476-9, but since itwas considered that insufficient tests have so far been carried out to establishreproducibility between laboratories, it has been decided that the method cannotyet be given the full status of a British Standard in the BS 476 series.

The need for a glossary covering terms used in BS 476 has been established andthis has been published as BS 4422 Glossary of terms associated with fire, withthe following Parts:

Part 1: The phenomenon of fire;

Part 2: Building materials and structures;

Part 3: Means of escape;

Part 4: Fire protection equipment;

Part 5: Miscellaneous terms (in course of preparation).

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Foreword

A fire may create a hazard to neighbouring property. The extent of the hazarddepends on the distance separating a building from the fire, the size and severity

of the fire and the amount of the heat received on a building. The chief dangerarises from radiated heat combined with the burning embers (flying brands)thrown off from the fire.

The tests described in this Part of BS 476 are designed to give information on theability of a roof covering and its supporting deck or supports to act as a protectivebarrier against a fire in a nearby building and on the extent of any surfaceignition. Provision is also made for the testing of rooflights, domelights andsimilar components. Whilst the test has been designed to give information on theperformance of a roof to external fire exposure in a building situation, the resultsobtained do not necessarily show how the roof will behave in any particular fireand therefore should not be considered as an overall indication of the potentialfire hazard. No information is obtained from the test on the performance of theroof when subjected to conditions of an internal fire.

When subjected to the performance test the specimen is exposed to radiant heatwhich can be regarded as, for example, the intensity incident on a roof 7.5 mabove ground level from a fire 13.5 m away in a building with a facadeof 15 m 15 m and 50 % window openings.

A gas flame is employed in the test to represent flying brands falling on the roof.

In this revision of the standard the following modifications have been made.

a) The separate spread of flame test has been dropped and in its place ameasurement of the extent of surface ignition is made at the same time as thepenetration test using the same level of radiation intensity. This change alsoavoids confusion with the surface spread of flame test now covered in Part 7which relates to the characteristics of wall and ceiling linings under internal

fire conditions.b) The requirements for suction under the roof specimen for the purposes ofsimulating the effects of a wind on the upper surface of a roof has been omitted.The requirement was found to interfere with observation of the underside ofthe specimen due to the presence of smoke within the enclosed specimenholder.

c) To extend the field of application of the test, provision has been made forincreasing its duration if required.

d) The penetration of fire and surface ignition measurements being combinedin one test reduce the number of specimens to be tested. The specimen size hasbeen increased to 1.5 m 1.2 m to provide a sufficient area for measurementof surface ignition and at the same time permit a more representativeconstruction to be tested.

e) The previous method required the test flame to be applied only once duringthe early part of the exposure. This was considered to be unrealistic and in therevised method the test flame is applied at intervals during the test.

f) The performance of the specimen was previously expressed in terms ofdefinite designations. These designations are replaced by the actualperformance data. The above mentioned designations were used for thepurposes of building control by grouping certain performance classifications inrelation to type of buildings and distance from the boundary.



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The following table shows examples of the relationship between existinggroupings and the new method of expressing a similar performance for

penetration.

Extent of surface ignition characteristics are not included in the newdesignations given in the above table. In some situations it may be necessaryadditionally to control these characteristics for which the test report providesfull details.

NOTE The category designations used in the previous edition of this standard were two letters.The first letter referred to penetration times of the specimen, where penetration had occurred in

A for not less than 1 h, B for not less than 30 min, C for less than 30 min and D during thepreliminary flame test. The second letter referred to spread of flame of the specimen whichoccurred, A none, B for not more than 21 in (533.4 mm), C for more than 21 in (533.4 mm) and Dwhich continued to burn for 5 min after withdrawal of the test flame or spread morethan 15 in (381 mm) across the region of burning in the preliminary test. Suffix X to categorydesignations denoted dripping from the underside of the specimen tested, and this is now includedas a part of the test report.

g) A simulated gutter is positioned at the front end of the specimen to collectany molten materials which may flow from the surface of the specimen duringa test.

h) An additional section gives the minimum information that should beincluded in a test report.

Attention is drawn to the Health and Safety at Work etc. Act 1974, and the needto ensure that the methods of test specified in this standard are carried out undersuitable environmental conditions to provide adequate protection to personnelagainst the risk of fire, inhalation of smoke and/or toxic products of combustion.

BSI has established OC/10, Co-ordinating committee on fire tests, and as a resultof the work of this committee it may be necessary to amend this standard at afuture date.

This standard is expressed in metric terms.

A British Standard does not purport to include all the necessary provisions of acontract. Users of British Standards are responsible for their correct application.

Compliance with a British Standard does not of itself confer immunityfrom legal obligations.

Part 3:1958 Part 3:1975

AA, AB, AC P60a

BA, BB, BC P30

AD, BD, CAP15

CB, CC, CD

Unclassifiable P5a P60 means that the specimen passed the preliminary test (see 6.2) and that fire

penetration (see 6.3) did not occur in less than 1 h.

Summary of pages

This document comprises a front cover, an inside front cover, pages i to iv,pages 1 to 6, an inside back cover and a back cover.

This standard has been updated (see copyright date) and may have hadamendments incorporated. This will be indicated in the amendment table onthe inside front cover.

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1 Scope

This Part of this British Standard specifies tests

which are designed to measure:

a) the ability of a representative section of a roof,rooflight, domelight and similar components toresist penetration by fire when the externalsurface is exposed to heat radiation and flame;

b) the extent of surface ignition of the uppersurface with and without supporting radiation.

2 References

The title of the British Standard referred to in thisstandard is given on the inside back cover.

3 Definitions

For the purposes of this British Standard thefollowing definitions and those given in BS 4422apply.

3.1specimen of roof construction

all constituents comprising the roof covering(including any associated membrane or insulatingmaterials fixed above the supporting members)together with the roof slab or decking in contacttherewith and the supports thereto but excludingany ceiling or soffit beneath such decking orsupporting members

NOTE Where the roof covering is intended to be used inconjunction with a stressed skin deck construction the deckingshall be a representative section comprising the top skin togetherwith any joist or similar supports.

3.2penetration time

the time at which glowing or flaming appears on theunderside surface of the specimen or the time atwhich the formation of holes or fissures or collapseof specimen occurs, whichever is the earliest. Forthis purpose a hole or fissure includes any aperture

through which the test flame can be observed fromthe underside when it is applied to the upper surface

3.3extent of surface ignition

the maximum distance of lateral flame spread onthe upper surface

4 Test specimen

4.1 Construction of specimens. The test

specimen shall be representative of the roofconstruction including at least one example of eachjoint, if any used, in each of the materials employedin the construction. Any joints in the roofconstruction shall be so arranged to occur in thecentral part of the specimen. The specimen edgesshall be sealed with strips of a non-combustiblematerial such as 12 mm thick asbestos board, thetops of the strips being flush with the upper surfaceof the specimen.

NOTE If information is required on the behaviour of thespecimen with eaves or verges, these may be included in theconstruction.

4.2 Size of specimens. The overall size of thespecimen, excluding the sealing strips, shall be notless than 1.5 m 1.2 m (see Figure 1). If thespecimen is a rooflight or similar component whichis only available in a size other than specified, thenext smaller component shall be tested and properlyfitted in accordance with 4.1 into the centre of apanel 1.5 m 1.2 m of an appropriatenon-combustible roof construction.

4.3 Number of specimens. Four specimens shallbe provided.

4.4 Conditioning of the specimens. The

specimens shall be conditioned to equilibrium in anatmosphere at a temperature of 10 C to 21 Cand 55 % to 65 % relative humidity. They shall betested as soon as possible after leaving theconditioned atmosphere; the interval betweenremoval from this atmosphere and testing shall notexceed 4 h.

5 Test equipment

5.1 Test environment. The test equipment shallbe located in a draught-free atmosphere. In order tomaintain the calibration of the equipment during

the course of a test it is recommended that thevolume of the test enclosure be not lessthan 1 300 m3 and the floor to ceiling height be notless than 5 m.

5.2 Heating panel. The heating panel shall consistof four 300 5 mm2 radiant heaters mounted on asteel flamework so that their centres occur at thecorners of a square having 480 mm sides. Theheating panel assembly shall be capable ofmovement between a position 10 to 45 to thehorizontal.



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Before a test the heating panel shall be controlled toprovide a maximum incident radiation intensity

of 14.6 0.5 kW/m2

at the centre of the surface ofthe specimen measured by a radiometer. Theapparatus shall be calibrated to give thedistribution of radiation intensity in the plane of theupper surface of the specimen at nine positions asshown in Figure 1. These intensities shall bemeasured without a specimen being in place.

The monitoring of radiation intensity before a testshall be by means of four radiometers placedsymmetrically in front of the radiant heaters at thecorners of a square of 610 mm side. A suitablemethod is to use copper asbestos disc radiometers,as described in appendix A, placed at a distance

of 125 mm in front of the radiant heaters.

5.3 Test flame. The test flame shall consist of aluminous coal (simulated town) gas or natural gasflame 200 mm to 250 mm long issuing from a tubewhen held in a vertical position with an orificeof 9 0.5 mm diameter (see note). The tube shall beprovided with a flexible length of pipe so that thetest flame can be moved over the surface of thespecimen.

NOTE It has been found that this can be achieved when usingcoal (simulated town) gas (calorific value 4 450 kcal/m3) at a flowrate of approximately 3 730 cm3/min or natural gas (calorific

value 10 730 kcal/m3) at a flow rate ofapproximately 1 550 cm3/min.

5.4 Specimen holder (see Figure 2). The specimenshall be supported by a metal framework that allowsan unobstructed view of the underside of thespecimen and does not restrict its thermalmovement. The frame shall be provided with meansof adjustment for the height of the specimen and itsangle of inclination from 1 to 45 to the horizontal.The specimen on its frame shall be capable ofmovement from an unexposed position to the testposition within 5 s. A metal gutter extending thefull width of the specimen shall be fitted to the front

of the frame, located about 50 mm below the frontedge.

Figure 1 Diagram showing radiation intensities at nine positions on plan ofspecimen for calibration

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Figure 2 Typical roof test apparatus



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6 Test procedure

6.1 Mounting of specimens. Each specimen shall

be mounted with its upper surface at an angle of 45to the horizontal. If the specimen represents aconstruction which is intended to be used at a lesserangle, then the appropriate slope shall be used inthe test with a minimum slope of 1.

6.2 Preliminary ignition test. One specimen shallbe supported as specified in 5.4 and the test flame,specified in 5.3, shall be applied to its upper surfacewithout incident heat radiation. The orifice throughwhich the flame is issuing shall be held 5 mmto 10 mm from the surface at the centre of thespecimen with the tube held at an angle to enable

the flame to maintain contact with the uppersurface. The flame shall be removed 1 min afterapplication and observations made of any continuedflaming on the upper surface and fire penetration tothe underside. If penetration occurs the subsequenttests shall not be carried out.

6.3 Fire penetration and surface ignition test

6.3.1 Three specimens shall be tested. The heatingpanels shall be stabilized to provide the radiationintensity on the upper surface of the specimen asspecified in 5.2. This is normally achieved at adistance of 580 5 mm from the plane forming theradiant heaters, the distance being measured atright-angles to the centre of the specimen.

6.3.2 The specimen shall be moved from theunexposed position to the test position within 5 s.The test starts at the moment the specimen is in thetest position. The test shall be of at least 60 minduration, unless penetration occurs earlier. The testperiod may be extended beyond 60 min to amaximum of 90 min.

6.3.3 The test flame shall be applied over the uppersurface of the specimen for a period of 1 min, the

first application being at 5 min from the start of thetest. Throughout the duration of the test successiveapplications shall be made at 5, 10, 15, 30, 45and 75 min from the start of the test unless the testhas been terminated at an earlier time. The testflame shall be directed towards the top edge of thespecimen (see Figure 1) with the orifice 5 mmto 10 mm from the surface of the specimen and thetube held at an angle to enable the flame tomaintain contact. At each application of the testflame it shall traverse the specimen from one sideedge to the other at least once, in a direction parallelto the XX axis (see Figure 1) and so as to pass over

the central area of the specimen. Where rooflightsare incorporated the path of the pilot flame shouldbe as shown in Figure 3. The test flame shall bemoved slowly over the surface at an average speedof 2 m/min covering joints and other positions whichappear susceptible to flaming; it may be held at anypoint for up to 15 s if ignition of the surface seemsimminent.

6.3.4 Immediately following the application of theflame to the surface of the specimen the test flameshall if required be applied to any molten materialcollecting in the gutter.

6.4 Test observations. The following observationsshall be recorded in respect of each specimen.

a) The time and occurrence of any flaming on theupper surface and its duration. Where sporadic orintermittent flaming occurs without ameasurable progression of the flame front, itshall be recorded under other observation[see clause 8 e)].

b) The time at which glowing or flaming appearson the underside.

c) The time of development of holes or fissures, orcollapse.

d) Visual changes in appearance.e) Any fall of molten materials into the gutter atthe front or from the underside of the specimenand any flaming of the molten material.

f) Behaviour at eaves when these areincorporated.

g) The maximum distance of lateral flame spreadon the upper surface which has occurred at anytime during the test shall be measured to thenearest 25 mm, as follows:

1) maximum spread in any direction in thepreliminary ignition test (see 6.2);

2) maximum spread measured along the XXaxis (see Figure 1) in the fire penetration andsurface ignition test (see 6.3).

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6.5 Test results

6.5.1Preliminary ignition test. If the duration offlaming exceeds 5 min after the withdrawal of thetest flame or if the maximum distance of flaming inany direction exceeds 370 mm, the performance ofthe specimen shall be expressed by the letter X. Ifthe duration of flaming after the withdrawal of thetest flame is less than 5 min or if the maximumdistance of flaming does not exceed 370 mm, theperformance shall be expressed by the letter P. Ifpenetration of fire occurs in this test the penetrationtime for the whole sample shall be reportedas 1 min.

6.5.2 Fire penetration and surface ignition test. Thepenetration time to the nearest minute shall begiven for each specimen. If no penetration hasoccurred, the time shall be taken as the maximumduration of the test.

The extent of surface ignition shall be given for the

three specimens at 60 min or at the time ofpenetration to the nearest 25 mm.

7 Expression of results

The results obtained for each roof specimen testedshall be given as follows.

a) Inclination of the roof.

b) Performance in the preliminary ignition test.

c) The penetration time in minutes.

d) The extent of surface ignition in millimetres.

8 Test report

The test report on the specimens shall include thefollowing information.

a) Name of testing laboratory.

b) Name of sponsor.

c) Date of test.

d) Complete description of construction andconditioning of test specimens.

e) Test results, as specified in clause 7 includingany observations under 6.4.

Figure 3 Path of travel of pilot flame



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Appendix A Copper asbestos discradiometer

The copper asbestos disc radiometer is constructedfrom a copper disc, 0.376 mm thick and 25.4 mmdiameter, to which is soldered chromel andconstantan thermocouple wires, 0.719 mmdiameter. Discs of asbestos paper, 0.254 mmthick, 32 mm diameter and with a mass per unitarea of 175 g/m2, are secured to both sides of thecopper disc by sodium silicate adhesive. The sodiumsilicate adhesive consists of an aqueous syrup ofcomposition between Na2O:3.2SiO2 andNa2O:3.4SiO2, having a relative densitybetween 1.41 and 1.43.

The thermocouple wires are soldered to the copperdisc at diametrically opposite points near the edgeusing a high melting point solder (750 C). Aftersoldering, the disc is thoroughly cleaned on bothsides by dipping in a cleaning mixture consisting ofconcentrated sulphuric acid and chromic acid orsodium dichromate in the ratio 4 to 1 by volume.

After washing and drying the disc, care being takennot to handle the surface of the copper with the

fingers, a drop of silicate adhesive is applied to thecentre of the disc from a 6 mm diameter rod that hasbeen immersed to a depth of 30 mm in the silicateadhesive. The asbestos disc is then placed on topand worked round with the finger spreading theadhesive over its surface until it becomes tacky. Thedisc is then centralized and pressed down firmly.This process is repeated for the other side of the disc,care being taken to ensure that the asbestos paperis pressed down firmly round the thermocouplewires and is well sealed round the edge.

The completed copper asbestos disc radiometershould be used with the thermocouples side facing

the source of radiation.The output, in millivolts, from the radiometers isobtained from the following relationship:

4.187 E2 + 79.56E 100I= 0

where

E is the e.m.f. (mV);

I is the intensity of radiation (kW/m2).

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Publication referred to

This standard makes reference to the following British Standard:

BS 4422, Glossary of terms associated with fire.



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