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

Fire Service ManualVolume 2Operational

Firefighting Foam

The Fire ServiceCollege

* 0 0 0 8 6 3 8 3 S *

HM Fire Service Inspectorate Publications SectionLondon: The Stationery Office

Firefighting Foam

Crown Copyright 1998Published 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,S1. Clements House, 2-16 Colegate, Norwich. NR3 ISQ

ISBN 0 11 341186 3

Cover photograph:Northern Ireland Fire Brigade

Half-title page photograph:Northern Ireland Fire Brigade

Printed in the United Kingdom for The Stationery OfficeJ67054 12/98 C50 5673

Preface

This manual, Volume 2, Fire Service Operations -Firefighting Foam. deals with the production offoam, categories of fires and foams, applicationrates and the operational use of foam. Specificpractical scenarios are also discussed.

A second manual is also [Q be provided underVolume 1, Fire Service Technology, Equipmentand Media. This will deal with the technicalaspects of foam concentrates, standards andequipment.

These books will replace:

The Manual of Firemanship Book 3. Part 3

Dear Chief Officer Letter 2/97 - FoamApplication Rates.

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

Mr Bryan Johnson BSc.;Home Office Fire Experimental Unit;S.D.O. M. George, 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: andOr Tony Cash.

Home Office, September 1998

Firejighling FoamIII ~

_______________________11

Firefighting Foam

ContentsPreface

Chapter 1 Introduction

Chapter 2 Production of Finished Foam2.1 General2.2 Percentage Concentration2.3 Aspiration2.4 Foam Expansion Ratios

Chapter 3 Categories of Fir and Firefighting Foams3.1 Classes of Fire3.2 Electrical Fires3.3 Types of Liquid Fuel Fire

Chapter 4 Re 'ommended linimum Application Rates4.1 General4.2 Fires Involving Water-immiscible Class B Liquids4.3 Fires Involving Water-miscible Class B Liquids

Chapter 5 Operational Use of Foam on Cia B Liquid Fuels5.1 General5.2 Low Expansion Foam5.3 Medium Expansion Foam5.4 High Expansion Foam

Chapter 6 Practi al cenario6.1 General6.2 Preplanning6.3 Scenarios

Chapter 7 Storag Tank Fires

iii

1

33445

99

1313

17171717

2121222829

35353535

497.17.27.37.47.5

IntroductionCommon Problems With Refineries and Storage Tank FarmsTank SizeFire DevelopmentPractical Scenarios

4949505052

Firejighling Foam V [

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Chapter 8 Logi tic of Dealing With Larg8.1 Introduction8.2 Conventional Fire Attack8.3 Technical Options

References

Further Reading

Glossary of Terms - Firefighting Foams

VI Fire Service Mallual

Storage Tank e1 ire 65656574

87

87

89

Firefightin Foam

Firefighting Foam Ch pte

Chapter 1 - Introduction

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 fin-ished foam, once formed on the fuel, tostay intact when subjected to heat and/orflame.

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.

leads to the complete destruction of the foamblanket. Consequently, special firefighting foams,generally known as 'alcohol resistant' foam con-centrates, have been developed to deal with theseparticular types of liquid.

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

Sealing and resealing: the ability of thefoam blanket to reseal should breaks occurand its ability to seal against hot and irregu-lar shaped objects.

Contamination resistance: the ability of thefinished foam to resist contamination by theliquid to which it is app[ied.

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

Water is used for most firefighting incidents,however it is generally ineffective against firesinvolving flammable liquids. This is becausewater has a density that is greater than most flam-mable liquids so, when applied, it quickly sinksbelow their surfaces, often without having anysignificant effect on the fire. However, whensome burning liquids, such as heavy fuel oils andcrude oi Is, become extremely hot, any water thatis applied will begin to boil. The resulting rapidexpansion as the water converts to steam maycause burning fuel to overflow its containmentand the fire to spread - this event is known as aslop-over. Also, the water that sinks below thefuel will collect in the container and, should thecontainer become full, this will result in the fueloverflowing.

Finished firefighting foams, on the other hand.consist of bubbles that are produced from a com-bination of a solution of firefighting foam concen-trate 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 low 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 sol-vents, can pose additional problems for firefight-ers. These quickly attack finished foams byextracting the water they contain. This rapidly

Firefighting Foam 1

Firefighting Foam Chapter

The performance of firefighting foams can begreatly influenced by:

The type of foam-making equipment usedand the way it is operated and maintained.

The type of foam concentrate used.

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 effec-tive risk assessment at the commencement of anincident is of the utmost importance to ensurethat the correct foams, equipment and tacticsare selected and employed.

Chapter 2 - Production of Finished Foam The type of fire and the fuel involved.

2.1 GeneralFinished foam is produced from three main ingre-dients; 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 pro-portions (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 solu-tion. In other words, the foam concentrate andwater have been mixed together prior to arrivingat the foam-making equipment. Occasionally, pre-mix solutions are produced by mixing the correctproportions of water and foam concentrate in acontainer. such as an appliance tank, prior topumping to the foam-making equipment. In addi-tion, some types of foam-making equipment are

FinishedFoam

fitted with a means of picking up foam concen-trate at the equipment; these are known as 'self-inducing' with [he 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 rela-tively 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 by thenozzle. to the volume of the foam solution used toproduce it, is 20: I or less. Other equipment isavailable which can produce medium expansionfoam (MX) with expansion ratios of more than20: 1 but less than 200: I, and high expansion foam(HX) with expansion ratios of more than 200: I andpossibly in excess of 1000: 1.

1Venturi

ProportionerWater

Figure 2./ Theproduction offinishedfoam

The tactics of foam application.

This Volume of the Manual describes all aspects ofthe operational use of firefighting foam and in par-ticular its use against class B liquid fuel fires.Topics covered include recommended minimumapplication rates and application techniques; prac-tical scenario considerations; and the logisticsinvolved in dealing with fires in storage tanks.

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

The length of pre-burn.

The quality of the water used.

The rate at which the foam is applied.

The section on firefighting foams in Volume I ofthe Manual describes the technical aspects of fire-fighting foam and discusses the types of equip-ment 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. However, themore important operational aspects included inVolume I are also summarised in Chapters 2,3 and4 of this Volume. At the rear of this Volume, thereis a glossary of terms used in this Manual andother terms that may be used in connection withfirefighting foams.

2 Fire Sel'l'ice Manual Firefighting Foam 3

As it leaves the branch.

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

When it strikes an object. This causes fur-ther turbulence and air mixing. 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

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.

2.4 Foanl Expansion Ratios

(a) General

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 vol-ume of the finished foam to the volume of thefoam solution used to produce it.

(b) Equipment Used For GeneratingDifferent Expansion Ratio Foams

Typical firefighting foam expansion ratio rangesare:

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

Primary aspirated low expansion foams are usual-ly produced by using purpose designed foam-mak-ing branches or mechanical generators.

Secondary aspirated low expansion foams are usu-ally produced by using standard water deliverydevices. Some purpose designed large capacitymonitors have also been produced for this particu-lar type of application (see Chapter 8, Section 3).

Medium and high expansion foams are usually pri-mary 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.

As it travels through the air due to the tur-bulence produced by the stream.

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

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. However,foam blankets with short drainage times can beadvantageous if rapid film-formation on a fuel isrequired (see this Chapter, Section 4c).

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

Secondary aspirated foam - finished foamthat is produced by all other means, usuallystandard water devices.

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

Consequently, the term 'non-aspirated foam' isoften used incorrectly to describe the product of afoam solution that has been passed through equip-ment that has not been specifically 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:

It is highly unlikely that a foam solution can beapplied operationally to a fire in such a way that noaspiration occurs. However, should such circum-stances occur, then this would be referred to as anon-aspirated application. Some water additives,

Water

Foam Concentrate

Figure 2.2 6% Foam Concentrate 94% Water

2.3 Aspiration

It is also very 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 oper-ating correctly and giving an accurate rate ofinduction.

a foam solution rich in foam concentrate. Not onlywill this result in the foam supply being depletedvery quickly and an expensive waste of foam con-centrate, but it will also lead to finished foam withless than optimum firefighting performance, main-ly due to the foam being too stiff to flow ade-quately. Alternatively, using 3% foam concentratewhere the system is set for I % will result in a solu-tion with too little concentrate to make foam withadequate firefighting performance.

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

Aspirated foam is made when the foamsolution is passed through purpose designedfoam-making equipment, such as a foam-making branch. These mix in air (aspirate)and then agitate the mixture sufficiently toproduce uniformly sized bubbles (finishedfoam).

3% concentrates3 parts foam concentrate in 97 parts water,

All foams are usually supplied as liquid concen-trates. 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 asfollows:

6% concentrates6 parts foam concentrate in 94 parts water,

I % concentrate is basically six times as strong as6% concentrate. and 3% concentrate is twice asstrong as 6% concentrate. However. the firefight-ing characteristics of finished foam produced from1%, 3% and 6% concentrates of a particular typeof manufacturer's foam should be virtually identi-cal.

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

2.2 Percentage Concentration

1% concentratesI part foam concentrate in 99 parts water.

The lower the percentage concentration, the lessfoam concentrate that is required to make finishedfoam. The use of say 3% foam concentrate insteadof 6% foam concentrate can result in a halving ofthe amount of storage space required for the foamconcentrate, with similar reductions in weight andtransportation costs, while maintaining the samefirefighting capability. Not all foam concentratesare available in the highly concentrated I% form,e.g. alcohol resistant and protein based foam con-centrates. This is because there are technical limitsto the maximum usage concentrations of some ofthe constituents of foam concentrates.

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 creating

4 Fire Service Manila! FireJighting Foam 5

(c) Foam Concentrates

Figure 2.3Diagrammaticillustration ofexpansion of differentfoam types.

Primary Aspirated Finished Foams

warehouses, aircraft hangars, cellars,ships 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.

Medium expansion finished foam can only beprojected over small distances. However, withexpansions of between 20 and 200, large quantitiesof foam are produced from relatively small quanti-ties of foam solution. This, combined with its abil-ity to flow relatively easily, makes medium expan-sion foam ideal for covering large areas quickly.

such 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 aspi-rated low expansion foam. This has resulted inequipment being designed specifically to projectsecondary aspirated foam into large storage tankfires (see Chapter 5, Section 2b) (iv) and Chapter8, Section 3). Manufacturers of this equipment rec-ommend the use of film-forming foam concentratetypes for such applications. They claim that thefinished foam produced usually has an expansionratio of less than 4: I.

The amount that a foam solution can be aspiratednot only depends on the equipment, but also on thefoam concentrate that is used. For instance, syn-thetic 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), are mostly intended for use at lowexpansion, although they can also be used to pro-duce medium expansion foam.

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

(d) Typical Uses and Properties of Low,Medium and High ExpansionFinished Foams

The various expansion ratios are typically used forthe following applications:

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 as

t

High expansion finished foam flows directly outof the foam-making equipment and is not project-ed 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 moderate-ly strong wind conditions (Reference I).

The equipment used to produce secondary aspirat-ed foam is often standard water type branches andnozzles although there are some specificallydesigned nozzles available. The foam produced inthis way is not well worked, has a very low expan-sion ratio and short drainage time, and tends to bevery fluid. These properties, combined with thefilm-forming nature of the foam concentrates used,can result in a finished foam blanket that canquickly knockdown and extinguish fires of someliquid hydrocarbon fuels. This ability can makethem ideal for use in certain firefighting situations

6 Fire Sen'ice Manual Firejighting Foam 7

Firefig ting Foam h pt

Chapter 3 - Categories of Fire andFirefighting Foam

SecondaryAspiratedFinished Foams

Figure 2.4LolV expansion.Typical EffectiveProjection: 2' metres

Figure 2.5Medium expansion.Typical EffectiveProjection: 14 metres

Figure 2.6High expansion.Minimal Projection.(Photos: Mid and West WalesFire Brigade)

)

.1 Cia, e, of ire

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 combus-tion normally takes place with the for-mation of glowing embers.

Class B: fires involving liquids or liquefiablesolids.

Class C: fires involving gases.

Class D: fires involving metals.

Electrical fires are not included in this system ofclassification (see this Chapter, Section 2).

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

(a) Class A fires

Class A fires are those which involve solid materi-als 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 extinc-tion of class A fires. For these fires, AFFF, AFFF-AR. FFFP and FFFP-AR may be used at low andmedium expansion while SYNDET foams may beused at low, medium or high expansion.

There are said to be advantages in the use of wet-ting agents when fires become deep seated. Inthese conditions, water can be slow to penetrate. A

wetting agent that reduces the surface tension ofwater is claimed to greatly improve penetration tothe seat of these types of fire. When a wettingagent is employed, a deep seated fire is predomi-nantly 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 char-acteristics. From time to time, a few brigades takeadvantage of these wetting agent properties byusing AFFF not only for class B fires (see (b)below), but also, they claim, to make better use oflimited water supplies on Class A fires. It isclaimed that the increased cost in agent is oftenjustified by reduced 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 2). In particular, when applied by sprayto wooden crib fires, secondary aspirated AFFF,and to a slightly lesser extent, FFFP, AFFF-AR andSYNDET, performed significantly better thanwater. Several wetting agents were also tested butthey did not perform much better than water. Theseresults seem to indicate that wetting propertiesmay not alone quickly and effectively deal withClass 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).

During these tests, because of the size and shape ofthe fires, some areas of the cribs were not ade-quately reached by the spray. Consequently, testswere also performed using jet applications ofwater, primary aspirated AFFF and secondary

..

8 Fire Service MWIl/(/! Firefighting Foam 9

aspirated 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.

Medium and high expansion foam have beenadvocated for indoor use on class A fires. The con-finement provided by the walls of buildings allowsthe foam to accumulate into a thick blanket andalso protects the foam from being torn apart bywind. The mechanism put forward for extinguish-ment is that the foam cuts down the movement ofair which supports combustion. There is a coolingeffect as water from the foam evaporates, and thesteam generated will also tend to reduce the oxy-gen level in the air surrounding the fire. If the foamblanket is deep enough, it will exert enough down-ward pressure to enable it to refill holes opened upwhen the foam is destroyed by the heat from thefire. Materials and structural members that wouldotherwise be exposed are shielded from heat radi-ation by the foam.

Although high expansion foam can be effective,the main practical drawback is that firefighterscannot be sure that the fire has been extinguished(see Chapter 5, Section 4). It can be dangerous toenter a deep foam blanket to track down the seat ofa fire since there is a chance of sudden exposure toheat and products of combustion. Under someconditions, the fire can continue to burn for a con-siderable period at a reduced rate supported by theair released from the foam as it breaks down.

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 observa-tion whilst maintaining sufficient foam flow toforce the foam onto the fire.

(b) Class B Fires

(i) General

Class B fires are those which involve flammableliquids, liquefiable solids, oils, greases, tars, oilbased paints and lacquers (i.e. flammable and

combustible liquids). Combustion of these occursentirely in the vapour that is present above the sur-face of the liquid. For firefighting purposes, ClassB liquids can be subdivided into three categories,each requiring different properties from firefight-ing foams in order to achieve effective and effi-cient fire control and extinction.

The categories are:

high flash point water-immiscible Class Bliquids;

low flash point water-immiscible Class Bliquids:

water-miscible Class B liquids;

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.

However, most low flash point hydrocarbon fires,such as those involving petrol, cannot be extin-guished by water alone as the fuel cannot be low-ered to a temperature where the quantity of vapourproduced is too small to sustain burning. In addi-tion, water is generally much denser than liquidhydrocarbons, consequently, when applied duringfirefighting, it immediately sinks below their sur-faces without having any beneficial effect, in fire-fighting terms, on the fire. In fact, the applicationof water may cause the surface 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 pro-vides a visible blanket which controls and extin-guishes these fires faster and more effectively thanwater.

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

(ii) High Flash Point WaterimmiscibleClass B Liquids

Water-immiscible liquids with high flash points, orclass C petroleum liquids, are those with a flash

point above 55C such as gas oils, sbme diesel oils,heavy fuel oils and heavy lubricating oils. At nor-mal ambient temperatures these liquids have lowvapour pressures and so do not generate flamma-ble 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 com-bustion.

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.

The primary mechanisms by which foams extin-guish 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.

(iii) Low Flash Point Water-immiscibleClass B Liquids

Water-immiscible liquids with low flash points, orclass A and B petroleum liquids, have flash pointsbelow 21C and 5SOC respectively. These includeclass A petroleum liquids such as aviation gaso-line, benzene, crude oil, hexane, toluene and petrol(including lead-free), and class B petroleum liq-uids such as avtur jet fuel and white spirit.

Spills or pools of low flash point liquids can pro-duce flammable vapour under normal ambienttemperatures, and flammable or explosive concen-trations 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 gen-eration is not sufficiently reduced by the degree ofcooling achieved. However, considerable reduc-tions in flame height and radiation intensity can beachieved with water spray application. Obviously,care should be taken to ensure that the fuel doesnot overflow any containment. Where the fuel isnot contained, the application of water will resultin further fuel and fire spread.

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 pre-vents further vapour generation. Where deep foamblankets can be formed, such as in storage tankswith a large ullage, this process may be assisted bythe increased pressure exerted by the heavier blan-ket. Film-forming foams produce a thin film on thesurface of some of these class B liquids which mayalso prevent vapour escaping.

Additional benefits of using firefighting foams onthese liquids are that they cool the liquid surface,reduce the vapour generation rate, obstruct radia-tion from the flame to the liquid surface and reducethe oxygen leveL by the production of steam, wherethe foam, flame and liquid surface meet.

Lead, as lead tetra-ethyl (or lead tetra-methyl) hasbeen used for more than 60 years to improve thepelformance (octane rating) of the hydrocarbonmixtures that constitute petrol. However, since[974, health and environmental concerns have

Figure 3./ Large scale leSI in progress.(PhOfO: Fire E.\perirnenlal VIIi' J

10 Fire Service Manual Firejighling Foam 11

resulted 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.

Large scale fire tests have been carried out in theUK to establish whether lead-free petrol, conform-ing with current British and European standards.would present any problems to the fire serviceusing their standard low expansion foam equip-ment and techniques (Reference 3). The resultsshowed that providing brigades follow the HomeOffice recommended minimum application rates(see Chapter 4), no problems would be expectedwhen using good quality AFFF or FFFP againstpetrol formulations permitted by current and like-ly future standards. However, FP gave poor extinc-tion pert'ormances against lead-free petrols con-taining oxygenates although its burnback pelfor-mances were better than either AFFF or FFFP.

In recent years liquefied flammable gases havebecome an increasingly important source of fuel incommerce and industry. Increased use bringsincreased transportation of these liquids through-out 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).

Boiling points for these liquefied gases are lowand so in the event of spillage, rapid vapour pro-duction occurs. Due to the greater amounts ofvapour produced and the low buoyancy of coldvapour, the dispersal of this vapour is more prob-lematical 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 1,500 metresfrom a spilled pool of liquid whilst retaining a con-centration above the lower flammability limit.

phosphorous pentoxide. Other metal fires are treat-ed as class A fires, but in general the use of mediaother than foam or water is found to be more suit-able.

3.2 Electrica Fires

Firefighting foams are unsuitable for use on firesinvolving energised electrical equipment. Otherextinguishing media are available. Fires in de-energised electrical equipment are treated as eitherclass A or B as appropriate (see this Chapter,Section I).

3.3 Types of Liquid Fuel F're

(a) 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 isalso of particular importance when tackling class

B 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.

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 situa-tions may occur simultaneously. Even so, theyillustrate the principles involved.

(b) Spill Fires

Spill fires occur in unconfined areas oftlammable,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 sur-face on which the liquid stands. Because it isunconfined, a spill fire may cover a very largearea.

(iv) Water-miscible Class B Liquids

Polar solvents and hydrocarbon liquids that aresoluble in water (water-miscible) can dissolve nor-mal firefighting foams. Such liquids include somepetrol/alcohol mixtures (see above), 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 mem-brane 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 surface of polar liquids, avoiding plunging (seeChapter 5, Section 2).

(c) Class C Fires

Class C fires are those involving gases or liquefiedgases.

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.

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 explo-sive) cloud generated and hence reduces the possi-bility of ignition.

(d) Class D Fires

Class 0 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 and

Figure 3.2 Foam in use following de-energising of Iron.lformel: (NOle posilion of sand 10 conIC/in spillage.)(PhOlo: NOr/hem Irl'lolld Fire Brigade)

..

12 Fire Service Manllal

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Firefighlinf{ Foam ] 3

The main characteristic of spill fires is their rela-tively short burning times. If an average burn rateof 4mm 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 rup-tured fuel container and burn for a considerabletime. continuous leakage may replenish the spill ornumerous deep localised burning pools of fuelmay form over a large area.

(c) Pool Fires

Pool fires occur in confined pools of flammable, orcombustible, liquids which are deeper than 25mmbut 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 con-fined 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.

The difference between pool fires and spill fires isthat pools may, depending on depth. continue toburn 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 agai nst a sol id surface and allowingthe foam to run onto the fire, may be both desirableand a practical possibility if suitable surfaces areavailable (see Chapter 5, Section 2).

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 blan-ket 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 as

fast flowing characteristics. Adequate post firesecurity is also required.

(d) Spreading Fires

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 asdrainage systems and floor voids.

An early step in fighting a spreading fire is to stopthe flow of product to the flames whenever possi-ble. Water spray provides an excellent screenbehind which to approach the fire and close leak-ing valves for instance. The flow from a storagevessel can also be stopped by water displacementif there is sufficient ullage above the source of theleak. This method has been successful in the caseof a ruptured storage tank line. Water is pumpedinto the tank to raise the liquid fuel above the levelof the outlet line so that water, instead of product,flows from the broken line.

[f 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 dischargefrom 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 contain-ment. Sand bagging, diversion channels andpumping out are all useful techniques to help pre-vent breakdown of containment.

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 dis-charging fuel will also be on fire. It may be neces-sary to use dry powder to extinguish fires in flow-ing 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 blan-ket already formed.

(e) Running Fires

This term refers to the case when a burning liquidis moving down a slope on a broad front. The situ-ation is rare but extremely hazardous because ofthe rapidity with which objects and people in thepath of the flow can be enveloped. It is not possi-ble 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 effecti ve 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 fluoroprotein or film-form-ing alcohol resistant foams might be consideredmost suitable because of their stability. althoughother foams would also satisfactorily perform thetask.

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 adjust-ed 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 evacuat-ing in advance any area which could possiblybecome inundated.

(I) Other Terms

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.

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14 Fire Service Manual

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Firejighling Foam 15

Firefighting Foam

Chapter 4 - Recommended MinimumApplication Rates

Ch pt r

4.1 General

The application rate of a foam onto a fire is nor-mally 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 Recommended Minimum Application Rate isthe minimum rate at which foam solution is recom-mended to be applied to a fire. The rate assumesthat all of the foam made from the foam solutionactually reaches the surface of the burning fuel.

The recommended minimum application rateincludes a 'safety margin' to help to take intoaccount factors such as:

variations in the quality of foamconcentrate;

immiscible class B liquids. Also, reconunended dura-tions of foam application are included in the tables.

It should be noted that the figures given in Tables4. J and 4.2 relate to minimum foam solution appli-cation rates and times and assumes that all of thefinished 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 compen-sate for losses due to circumstances such as fall outof finished foam from the foam stream, adverseweather 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 accountfor foam losses.

variations in the quality of finishedfoam produced;

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

) )

some of the detrimental effects offorceful application.

The Home Office recommended minimum appli-cation rates for use by the UK fire service for firesinvolving water-immiscible class B liquids aregiven in Section 2 below. Advice is given concern-ing the application rates for fires involving water-miscible class B liquids in Section 3 below.

4.2 Fires Involving Water-immi cible Clas B Liquid

Tables 4. I and 4.2 give the minimum applicationrates of foam soJution recommended by the HomeOffice for use by the UK fire service when usingmanual firefighting equipment to apply low andmedium expansion foam to tires involving water-

In practice, the recommended minimum applica-tion 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,branches, proportioners and hoses.

4.3 Fire Involving Wa er O1i IblCia s B Liquid

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

the type of fuel;

the depth of fuel;

Firefighting Foam 17

Table 4.2: Home Office Recommended Minimum Application Rates Of Foam Solution For theProduction of Medium Expansion Foam For Use on Liquid Hydrocarbon Fuel (Class B) Fires

Table 4.1: Home Office Recommended Minimum Application Rates of Foam Solution For theProduction of Low Expansion Foam For Use on Liquid Hydrocarbon Fuel (Class B) Fires

Minimum Application Rate of Foam Solution Minimum Application Time(lpm/m2) (Minutes)

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

the type of foam;

the manufacturer of the foam;

the method of foam application.

Some of the most widely used water-miscibleliquids include:

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 particu larwater-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

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 min-utes and for tanks involving these fuels it shouldbe a minimum of 60 minutes.

Tanks TanksFuel FuelFlashpoint Flashpoint>40C =81m

TanksD>=45mD

Firefig ting Foam

Chapter 5 - Operational Use of Foamon Class B Liquid Fuels

Cbapller

5.1 General

This Chapter mostly concerns the main fire serviceoperational use of foam, that is on class B liquidfuels.

mean that the firefighters will be able tostand as far away from the fire as is possiblebut, also, the wind wil.l cause the fire plumeto angle away from them and so furtherreduce the radiant heat being experienced bythem.

When using foam operationally, there are a num-ber of basic, common sense procedures that needto be followed to help to ensure success, these are:

Objective of Foam Application: On arrivalat an incident, an immediate decision needsto be made on whether foam needs to beused and, if so, what is the objective that ishoped to be achieved by its application. Forinstance, is the objective to provide a tem-porary break in order to attempt a rescue orclose a valve, or is the objective to totallyextinguish the fire?

Collect Sufficient Resources: Before com-mencing foam application, ensure thatenough resources of foam, water, equip-ment, personnel etc. are collected togetherto enable the objective of foam applicationto be carried out successfully. Home Officerecommended minimum foam applicationrates (see Chapter 4) should. where possible,be used as the basis for calculations. If a fireis to be totally extinguished, then runningout of foam concentrate during applicationwill probably result in a complete re-involvement of the fire and completewastage of the resources already used.

Wind Direction: Obviously, foam can onlybe effective when it reaches the intendedtarget. Wherever possible, the foam streamshould be directed downwind in order toproject the foam over the maximum possibledistance. In fire situations, this will not only

Correct Operation of Equipment: Thefoam-making equipment must be usedunder the correct operating conditions offlow and pressure. Inductors and foam-mak-ing branches must be matched and the cor-rect foam concentrate for the fuel and thecorrect foam induction rate must be chosen.Care should be taken not to cover the airinlet holes of the foam-making branchbecause this will result in poor quality foambeing produced.

Gentle Foam Application: Foam applica-tion should be as gentle as possible.Forceful application, which is applyingfoam directly to the surface of a fuel, willgenerally result in fuel contamination of thefoam, increased breakdown of the foam, andincreased flame intensity and radiated heatfrom the area of application due to vigorousdisturbance of the surface of the fuel. Theoverall effect will be a dramatic reduction inthe effectiveness of the foam. In addition,forceful application to an existing foamblanket may cause breaks which reveal theunderlying fuel. If complete extinction hasnot been achieved when this occurs, then asignificant amount of burnback could result.

Continuous Foam Application: Once foamapplication has commenced, it should con-tinue without interruption until at Ileast theobjective of the foam application has beenachieved. Interruptions in foam application

Firefighting Foam 21

(ii) Forceful Application

finger/hand deflection application.

gentle direct application;

front sUIface indirect application;

waJllobject indirect application;

Of these, the front surface and wall/object indirectmethods are likely to produce the most gentleapplications of foam to the fuel surface during nor-mal firefighting operations. The finger/handdeflection method is best suited for nearby appli-cation of foam to residual flames. Each of thesegentle application methods is described below:

Gentle direct application involves applyingfoam to the surface of the fueL with the foam-mak-ing branch as far away from the fire as possible,

(Photo: A1id om) West Wales Fife Brigade)

of mixing of the foam with fuel causing the foamto become contaminated. Inevitably, some of thefuel within this contaminated foam will burn off,causing the partial destruction of the foam blanketas it does so.

Figure 5. J Low expansion foam-making branch in use.

In addition, when the foam stream hits the burningfuel, it causes a great deal of disturbance to the fuelsUlface which results in a considerable increase inflame intensity and hence radiant heat. This wi IIcause the partial breakdown of any existing foamblanket and also makes it very uncomfortable forthe firefighters to maintain their position.

(iii) Gentle Application

There are several gentle foam application tech-niques available which will reduce the impactvelocity of the foam stream. These are:

General

making capability should be maintained,resources replenished and remain ready forimmediate use until all hazards have beenremoved or neutralised.

(i)

Beware of Ignition of the Foam Blanket:Even with a thick foam blanket in place,operations involving possible ignitionsources, such as hot cutting, should be car-ried out with great care. Fuel contaminationof foam can occur during application andthe vapour from some fuels will penetratethe foam blanket. Complete involvement ofthe foam blanket in flame can happen with-in seconds if a contaminated foam blanket isignited - this can occur with all types offoam concentrate. Foam production capabil-ity must be maintained throughout any suchoperations.

Further discussion of these basic and other proce-dures follows with particular reference to the typeof finished foam (i.e. Iow, medium or high) beingused.

(a) Primary Aspirated Foams

5.2 Low Expansion Foam

Low expansion foam-making branches throw theirfoam over much longer distances than medium orhigh expansion foam-making equipment. Thislength of throw is generally enough to allow fire-fighters to tackle large, open, liquid fuel fires whilestanding at a distance from the fire where the radi-ated heat is bearable.

Forceful application of the foam, such as whenaiming a foam stream directly onto the sUIface ofa burning fuel, causes the foam to impact heavilyon, and penetrate below, the surface of the fuel('Plunging'). This leads to a considerable amount

Ideally, the application of the foam to the sur-face of the fuel should be as gentle as possible inorder to achieve the most effective performancefrom the foam.

Edge Fires: Long after the main bulk of afire has been extinguished, flames are likelyto persist around the edges of the foam blan-ket where it meets and attempts to sealagainst objects, such as hot metal containerwalls. These last flames are likely to requirea great deal of time and foam to extinguish.If stocks of foam run out at this stage, thefire may burn back completely. Applicationshould continue to be as gentle as possible,with consideration being given to usingmedium expansion foam if access andequipment permit. It is often better to rein-force the foam blanket near to persistentflames so that it flows over the area of itsown accord. Using water to cool the exter-nal walls of a metal container around thearea of flame can help to reduce the rate ofvaporisation of the fuel, and hence the inten-sity of the flames. In addition, the cooler themetal walls of a container, the easier it willbe for a foam blanket to seal against them,suffocating the remaining flames as it doesso.

will result in wasted resources. The foamapplication should at least be maintained atthe Home Office recommended minimumapplication rate (see Chapter 4).

Maintaining the Foam Coverage: Once afire has been extinguished or a toxiclflam-mable fuel has been covered with a foamblanket, foam application should continueuntil a thick foam blanket has been built up.However, the foam blanket will break downand loose its water content with time.Consequently it is important that the foamblanket is regularly replenished in order toensure continued protection from re-ignitionor vapour release. Where possible, the useof water jets or sprays should be avoided inthe vicinity of a foam blanket as these canalso cause the foam to break down.

Maintain Foam-making Capability: Evenafter the fire has been extinguished (or thevapour from flammable and/or toxic mater-ial has been suppressed) and a thick foamblanket has been built up, a significant haz-ard still remains. Consequently, the foam-

22 Fire Service Manual Firejighting Foam 23

using the full trajectory of the foam stream. Thisreduces the impact velocity of the foam due to theloss of speed of the foam stream as it travels throughthe air and the dispersion of the foam in the streamduring transit.

Another similar method is known as the 'rain-down' technique. This involves directing the foamstream almost vertically up into the air so thatwhen the foam stream reaches its maximumheight, it breaks up and the resulting chunks offoam 'raindown' onto the fire. This has two poten-tially serious drawbacks; the first is that any ther-mal updraft from the fire plume is likely to carrythe foam upwards and away from the surface ofthe fuel; the second is that the technique requiresthe foam-making branch, and the firefighter, to bepositioned relatively near to the fire.

Front surface indirect application involvesfoam being rolled or pushed onto the surface of thefuel by aiming the foam stream at a point in frontof the fuel and allowing the foam to build up. Withfurther applications of foam to this area, a raft offoam will begin to gently flow across the surfaceof the fuel. This method leads to very little fuelcontamination of the foam.

Wall/object indirect application involvesaiming the foam stream at a surface behind the fire(such as the sides of a storage tank) or at an objectin, or to the side, of the fire. By positioning thebranch at a suitable distance away from the object,the foam stream will have lost much of its energyby the time it hits the object. Further energy will belost on impact with the object with the result thatthe foam will slide slowly down the object andgently onto the surface of the fuel. A raft of foamwill form which, with further application of foamto the object. will increase in size and spread overthe surface of the burning fuel. This method hasthe additional advantage that it can be used to coolhot metal objects which might otherwise causeedge sealing problems.

Finger/hand deflection application invol vesthe firefighter placing his hand or fingers directly infront of the outlet nozzle of the foam-makingbranch so that the foam issues as a spray rather thana jet: greatly reducing the impact velocity of thefoam. This method is most suited to extinguishing

small residual fires from very close range. Onedrawback of this method is that it may disturb theexisting foam blanket and reveal some of theunderlying fuel.

Suitable hand protection must be worn. This tech-nique is not acceptable for use with large through-put foam-making branches where fingers may bebent back by the force of the foam stream. Careshould also be taken when using long foam-mak-ing branches to ensure that the firefighter is not putoff balance by trying to use this technique.'Blabber-mouth' foam-making branches haveflaps that can be opened and closed at the outletend of the nozzle. These deflect the foam stream inmuch the same way as when using this method offoam application.

(iv) Single Point of Application

In order to achieve a quick flame knockdown withthe minimum of foam with a single branch, foamshould only be applied to one point and the branchshould be held still. This will allow a foam raft (or'bite') to form which will then spread over the sur-face of the fuel.

Moving the branch will result in many smallerapplications of foam which will not sufficientlycool the fuel locally or suppress the fire to allow anadequate foam blanket to form. This will lead to agreat deal of foam destruction, and hence wastage,of the finished foam.

When using more than one branch, a single pointof application should stiJl be used wherever possi-ble.

However, it should be noted that foam will onlyflow over a liquid fuel a maximum distance of 30metres from the edge of the foam application area(see Chapter 7, Section 5b(x)). Consequently,where the fire area is very large, several foamapplication points, and hence branches, will berequired. In such cases, the number of applicationpoints should be kept to the absolute minimum thatallows the foam blanket to cover the whole of thefire area.

One method of assisting in the spreading of foamover the surface of a fuel once a bite has been

achieved is by producing a swirling motion inthe whole surface area of the fuel. This can bedone by moving the branch or branches so that thestream(s) lands slightly off centre of the liquid sur-face (see Chapter 7, Section 5b) (xi).

(v) Assistance Required to Apply FoamAccurately

Usually, when applying low expansion foam, thefirefighter at the foam-making equipment will beunable to see where the foam stream is landing.Consequently, the firefighter may require helpfrom someone standing to the side who can seewhere the foam is being applied and can indicate,perhaps by the use of a radio or arm signals, whatmovements to the foam stream the firefighter mustmake in order to ensure the required applicationcan be achieved.

(vi) Extinction of Residual Flames

As mentioned previously, the extinction of anyresidual flames should, where possible, be by :

the use of medium expansion foam;

foam applied using the finger/hand deflec-tion application technique;

the gentle application of foam to the sur-rounding foam blanket in order to allowexisting foam to flow over the flames.

Some combination foam-making branches areavailable that allow the operator to easily switchfrom low expansion to medium expansion foam,these have obvious applications here. However,tests carried out by the Home Office FROG on onecombination 225 litre per minute foam-makingbranch indicated that it produced very poor lowexpansion foam which was unable to sufficientlycontrol a 56m2 petrol fire. Consequently, the fire-fighter was unable to get close enough to the firein order to use the medium expansion capability.

Forceful application of low expansion foam toresidual flames should be avoided due to the like-ly disturbance of the existing foam blanket whichmay reveal larger areas of underlying fuel and pos-sible re-ignition.

(vii) Continued Application After Extinction

Foam application should always continue afterextinction in order to produce a very thick protec-tive foam layer. It can take less than 4 minutes forhalf of the liquid content of a foam blanket to drainout. This may not have any effect on the appear-ance of the blanket but the loss of this amount ofwater will make the blanket less resistant to burn-back, less able to seal any breaks that may occur inthe blanket, more likely to allow vapour to perco-late through it, and make it more susceptible tobeing blown away by wind. Consequently, it isessential that the foam blanket is replenished atregular periods in order to maintain its effective-ness.

When replenishing, care should be taken to avoidapplying water initially to the foam blanket.Applying water will break down the foam blanket,cause gaps in the blanket to reveal the underlyingfuel and, in some situations, may produce a staticdischarge that could reignite the fire.

(viii) Precautions to Prevent Ignition of theFoam Blanket

Precautions should be taken to ensure that an igni-tion source does not come into contact with thefoam blanket. Rescue operations that take placewithin the foam blanket will inevitably lead tomuch disturbance of the foam blanket and furtherfuel contamination. Should foam that has beencontaminated with fuel ignite, then large areas ofthe foam blanket are likely to become involved inintense flames within seconds. These flames wjllprobably die down relatively quickly but leavingthe upper layer of foam badly damaged. Generally,the shorter and more forceful the foam application,the more severe any resulting fire is likely to be.

Crews should be on constantshmdby while operations takeplace to ensurc that adequatefoam and firefighting cover aremaintaincd. Should ignition uccur,the response must be immediate.

24 Fire Service Manual Firefighting Foam 25

Figure 5.2 Primary aspirated foam in use.rPhoto: WeSl Midlands Fire Service)

(ix) Ignition of Fuels Due to the StaticDischarge During FoamlWaterApplication

There have been several reports of floating rooftank fires that may have been ignited by the dis-charge of static electricity that had been generatedby the over-the-top application of water and/orfoam to refined hydrocarbon liquids (e.g. naphtha)following the sinking of the roof.

As a precaution, if foam is to be applied to a largehydrocarbon storage tank (greater than 500m3)where the roof is no longer present, and there is arisk of ignition of the contents of the tank, thenfoam should be applied via the sides of the tank.This gentle application method will allow foam toflow down on to the surface of the fuel and form acontinuous raft of foam. Islands of foam that arenot attached to the main raft should be avoidedbecause these may cause a static discharge whenthey reach the tank sides.

The impact of water or foam streams directlyon the tank contents should also be avoided asthis may produce a static discharge.

(b) Secondary Aspirated Foams

(i) General

At low expansion, film-forming foams (e.g. AFFF,AFFF-AR, FFFP, FFFP-AR) can be applied prima-ry aspirated, with the techniques described above,or they can be applied secondary aspirated. Onlyfilm-forming foams can be applied secondary aspi-rated, non film-forming foams such as P, FP andSYNDET must not be applied in this way.

(H) Application Techniques

Film-forming foams can be applied secondaryaspirated by using standard water-delivery branch-es set to wide angle spray or fog. The use of sprayor fog produces a relatively gentle application and,

on some fuels, this will allow a film to form on thesurface of the fuel.

Application should be made directly to the surfaceof the burning fuel. This requires the firefighter toget very near to the fire although a suitable spraypattern should provide sufficient protection fromradiant heat. The method of application generallyrecommended is to spray the secondary aspiratedfoam across the burning fuel with a sweepingaction, back and forth.

See Section (iv) below regarding the applicationtechnique when using purpose designed secondaryaspirated foam making branches.

(iH) Limitations of Use

The expansion of secondary aspirated foam is verylow, generally less than 5. On some fuels fires, itsuse can result in very quick control and extinc-tions. However, tests have indicated that secondaryaspirated film-forming foams can take up to twiceas long to extinguish a petrol spill fire as that takenby the same film-forming foams when used prima-ry aspirated (Reference 4).

On some of the more volatile hydrocarbons(including some blends of petrol), secondary aspi-rated foam has limited security and burnback resis-tance. Consequently, it should not be used forvapour suppression. If possible, after its use toextinguish a fire, a primary aspirated foam blanketshould be applied to provide adequate burnbackprotection.

Secondary aspirated foam is not suitable for use onwater-miscible fuels, even when alcohol resistantfilm-forming foam concentrates are employed.

(iv) Use in Specialised FirefightingEquipment

Some purpose designed secondary aspirated foam-making branches have been designed for use inprocess areas and/or for incidents involving largestorage tanks. This equipment is claimed to throwfoam solution over a greater distance, and up to agreater height, than is possible with primary aspi-rating equipment. This makes this type of equip-ment suitable for the protection of large storage

tanks. However, with this type of equipment, bythe time the foam solution has been projected to itstarget, its expansion ratio can be of the order of 4: Ito 6: I. Consequently, application techniquesshould, where possible, be as those given abovefor primary aspirated foam.

(c) Water-miscible Fuels

Only primary aspirated alcohol resistant typefoams should be used to fight fires that involvewater-miscible fuels. These should be applied asgently as possible to the fuel surface using thetechniques described in this Chapter, Section 2.Forceful application of alcohol resistant foams towater-miscible fuels will drastically reduce theirfirefighting capabilities due to contaminationwhich will quickly break down the finished foam.Non-alcohol resistant foams such as AFFF, FFFP,FP and so on, should not be used on these types offuels because the finished foam disintegrates oncontact with the fuels.

(d) Large Fuel Storage Tanks

For many years, the recommended technique forthe application of foam to fully involved largestorage tank fires required a number of foam-mak-ing monitors to be positioned around the tank, eachapplying foam to a small area. This technique wasknown as 'surround and drown'.

This required long periods of foam applicationbefore sufficient cooling of the fuel and knock-down of the flames occurred to allow small areas offoam to become visible on the surface of the fuel.

This technique has now been mostly rejected infavour of applying large quantities of foam to asmall area of the burning fuel surface. This pro-vides a very high localised foam application ratewhich relatively quickly results in the localisedknockdown of flames and the formation of a raft offoam (or 'bite') in the foam application area. Onceformed, this raft of foam gradually enlarges andspreads across the surface of the fuel. The maxi-mum distance this will spread is 30 metres in alldirections (see Chapter 7, Section 5b(x from theedge of the foam application area. Consequently,when fighting fires with large fuel surface areas,more than one main foam application point will be

26 Fire Service Manual Firefighting Foam 27

needed in order to ensure that the rafts of foamformed meet and hence cover the whole of the areaof fuel. The number of monitors this requires willobviously depend on their capacity but should alsotake in to account the maximum foam spread dis-tance of 30 metres. The aim should be to use theminimum number of foam application points pos-sible and, where necessary, several monitors canbe positioned to apply foam to the same point onthe fuel surface.

Once a bite has been achieved, the spread of foamacross the surface of the fuel can be aided by caus-ing the fuel to slowly swirl around the tank. Thismovement can be achieved by allowing the streamfrom a monitor to land slightly off centre of thefuel surface (see Chapter 7, Section 5b) (xi)).

5.3 Medium Expansion Foam

(a) General

Medium expansion foam can have relatively lowstability and poor burn back resistance and it is thesheer volume of foam produced, combined with itsinherent gentle application, that makes it an effi-cient and effective firefighting medium.

Figure 5.3 Medium expansion/oam in use i/1 a tank bUild.(PholO: A1id and We.\'{ ~yl/('s Fire Brigade)

For example, MX foam has a much greater volumethan low expansion foam. From the same amountof foam solution, a medium expansion foam gener-ator producing finished foam with an expansionratio of 100: 1 creates 10 times more finished foamthan a low expansion foam-making branch produc-ing foam of an expansion of 10: 1. Typically, medi-um expansion foam-making equipment producesfoam of expansions of between 50 and 100: l.

In order to make medium expansion foam, largequantities of air need to be mixed with the foamsolution. This mixing takes place within the foam-making equipment and this greatly reduces thespeed at which the foam emerges from it.

As a result, using medium expansion foam againstlarge fires can require firefighters to approach veryclose to the flames, exposing them to dangerouslevels of radiated heat. The risk to firefighters canbe reduced by the use of tloor standing mediumexpansion foam generators which, once in posi-tion, can be left unattended. It should be noted thathand-held medium expansion foam-making gener-ators should not be put on the ground while oper-ating because they may suck in debris which couldblock or break the internal foam-making mesh.

I II

The very gentle application characteristics and highvolume output of medium expansion foam makes itparticularly useful for rapid vapour suppression ofhydrocarbon liquids (and water-miscible liquidswhen using alcohol resistant film-folTIling foamconcentrates). It can also be used to fill, up to a max-imum height of around 3 metres, small volumessuch as those found in engine test cells and trans-former rooms.

The most common type of concentrate used to producemedium expansion foam is standard SYNDET,although FP and film-forming foams may also be used.

The Home Office recommended minimum appli-cation rates for medium expansion foam are virtu-ally the same as those for low expansion foamwhen used on hydrocarbon liquid fuel fires (seeChapter 4). However, Protein foam concentratemust not be used for the production of mediumexpansion foam and the limited throw of mediumexpansion foam is among the reasons why it can-not be used to fight large storage tank fires.

Medium expansion FP foam has been successful incontrolling crude oil bund fires with long pre-burntimes. The disadvantage of using medium expan-sion foams in these circumstances is that they donot release their water content quickly and there-fore their cooling ability is limited. Other disad-vantages of the use of medium expansion foam arethat they do not flow well, particularly in verywindy conditions and their heat resistance andability to seal against hot surfaces is also poor.

(b) Application Technique

To achieve the best possible fire knockdown,medium expansion foam should be applied in frontof a liquid pool fire and an initial foam raft ('bite')should be formed with little movement of thebranch. Further application of foam should then bethen be used to widen the raft to allow it to spreadover the surface of the fuel. This further applica-tion of foam should be to the edges of the raft, itshould not be to the flames in front of the raft.

(c) Use as a Fire Break

The Forestry Commission has experimented withthe use of MX foam in laying a barrier to grass,

heath and brush fires. Providing there is not toomuch wind, the foam remains in position and,besides the direct effect of stopping flames, thedrainage helps to create a wet surface to impedeany creeping fire. Application should be made notless than 5 minutes nor generally more than 60minutes before the fire front hits the barrier.

5.4 High Expan ion oam

(a) General

High expansion foam is produced from SYNDETsynthetic detergent concentrate. The finished foamhas an expan-sion ratio that can range from 200: 1to 2000: I although the high expansion foam gen-erating equipment used by the fire service normal-ly produces finished foam of expansion ratiosbetween 300: I and 1200: 1. High expansion foamcan be effective in extinguishing fires in a widerange of solid and liquid fuels.

From the same amount of foam solution, fire servicehigh expansion foam generating equipment can pro-duce, in terms of volume, in excess of 10 timesmore finished foam than medium expansion foam-making equipment and 100 times more finishedfoam than low expansion foam-making equipment.

The high expansion foam is very slow-flowing andis poured on to a fire rather than projected. It ismainly intended for use to totally 'flood' enclosedareas such as basements, warehouses, machineryspaces and ships' holds. It has also been used inhazardous areas where it can be unsafe to send per-sonnel, such as refrigerated rooms, mine shafts andcable tunnels. Due to the large volume of foamproduced from small amounts of foam solution,high expansion foam can also be used in instanceswhere there is a limited water supply and wherewater damage needs to be kept to a minimum.

High expansion foam can be very effective out-doors but only if the wind speed is very low.Outdoor uses include vapour suppression and, atlower expansions of the range, e.g. 300: J to 500: 1,in controlling fires in spiIJages of hydrocarbonfuels. Obviously. due to its density and the waythat it is produced, high expansion foam can onlybe applied very gently.

28 Fire Service Manual Firejighting Foam 29 r___________________________________________________...t.... .JI

Figure 5.4 A high expansion foam unit in operation.(PhOlo: Mid and Wesl Wales Fil,' Brigade)

The major disadvantages of using high expansionfoam for firefighting are:

the release of the water content of the foamis very slow and therefore this provides onlylimited cooling, particularly for deep seatedfires in combustible solids;

the foam does not flow well, consequentlythe foam will be at its lowest depth at thefurthest point away from the generator;

its poor flowing characteristics may alsolead to large air pockets in the foam wherecombustion can continue even after thecompartment has apparently been complete-ly filled,

the heat resistance of the foam and its abili-ty to seal against hot surfaces is poor;

due to large expansion ratios, high expan-sion foam is very light and can be blownaway by even a minor breeze and by the up-draughts caused by fires;

the foam cannot be projected and so thefoam generating equipment must be posi-tioned very close to fires. However, in cer-tain situations, flexible ducting can be usedto transport the foam to the required appli-cation area.

High expansion foam should not be used tofight fires involving chemicals which gener-ate enough oxygen to sustain their owncombustion, e.g. cellulose nitrate.

The slow release of water from the foam is benefi-cial when used for the vapour suppression of LPGand other similar liquefied gases.

Before the production of high expansion foambegins, as much information as possible must beobtained about any compartment that is about to beflooded, i.e. its nature, size, layout and contents. Ifthe contents of the compartment are stacked orplaced up to or near the ceiling, it must be realisedthat the foam blanket may not extinguish all of thefire, and preparations must be made to attack thislater. It must also be understood that the use ofhigh expansion foam will inhibit the use of any

other firefighting technique and may make it moredifficult to commit firefighters into the compart-ment at a later stage.

(b) Planning Resource Requirements

If the size of the compartment is known, it will bepossible to calculate approximately how muchfoam concentrate will be needed to adequately fillit. For compartments containing combustiblesolids, sufficient foam should be injected to ensurea depth of at least I metre above the highest fireaffected object. For flammable liquids, the fillheight should be considerably more than I metreabove the fuel surface.

To calculate the fill height, the approximate foamoutput of the particular high expansion foam gen-erator in use will need to be known in m3/min atthe required expansion ratio as will its consump-tion of foam concentrate in litres per minute.

A simple table kept with the generator would help,but allowances must be made for the initial fastbreakdown of foam that will occur due to the effectsof heat, flame and hot objects. Holes in the com-partment walls, and the need to regularly 'top-up'the foam for a ti me after control of the fire has beenachieved, will also need to be taken into account.

The minimum requirement should be to have suf-ficient high expansion foam generated to lift theheight of the foam in the compartment by at leastI metre per minute, with total filling of the com-partment to the required height taking no morethan 8 minutes. Resources should be made avail-able to 'top-up' the foam for at least a further 30minutes. In order to allow for the losses due to thebreakdown of the foam, at least a total of twice theamount of resources (i.e. foam concentrate andwater) required to fill the compartment to therequired height should be made available beforefilling commences. If high expansion foam is to beused outdoors, then further allowances will need tobe made for foam that is likely to be blown away.

(c) Positioning of High ExpansionFoam Generators

High expansion foam generators should always,where possible, be placed in the open air, as prod-

ucts of combustion of the fire could otherwiseaffect the volume output and stability of the foam.

Ducting can be used on the outlet of a generator toenable it to operate in fresh air while effectivelytransporting the foam to the required area. Thisducting should be kept as short as possible, with-out kinks, and any opening used must be larger incross-sectional area than the ducting, to cut downback-pressure and to ensure that the maximumpossible output can be generated. Doorways,hatches etc. may be usable as they are, but, in someincidents, openings may have to be made orimproved.

The further high expansion foam has to travelthrough ducting or other areas in order to reach thefire, the more breakdown of the foam that wi 11 takeplace. Ideally, the foam generator should be posi-tioned as near to the fire as it is as safe and practi-cal to do so. Tests have been carried out using lay-flat polythene ducting on the outlet of a highexpansion foam generator (Reference 5). Using an8 metre length of this ducting, the volume of thefoam produced by the generator fell by more than50%. However, even though this is a big reductionin the foam volume output, even less foam is like-ly to reach a fire affected area 8 metres away froma foam generator if ducting is not used.

There are various kinds of high expansion foamducting, but a heat-resisting type must obviouslybe used if the conditions demand it.

(d) Level of InjectionIf HX foam can be injected at the floor level of thecompartment, it will not have to contend with heat-ed currents of air to penetrate the area. However,operational conditions nearly always require it tobe injected at a higher level, and this will workprovided that the injection is kept going steadily.There will probably be an initial fast breakdown ofthe finished foam but the sheer volume shouldsoon penetrate.

(e) Ventilation

If a large volume of foam is to penetrate a com-partment, it must displace the air in that compart-ment. Also, when the foam first attacks the fire, a

30 Fire Service Manua! Firefighting Foam 31

(f) Maintaining Foam Production

considerable amount of the water in it will flash tosteam. All this, together with the products of com-bustion, will result in a back-pressure which. if notventilated, will physically prevent the injection ofmore foam.

Changes in the colour of the smoke issuing from thefire will give a good indication of whether the foamis achieving control of the fire. As mentioned above.there will be a degree of breakdown of the foam,and the application of high expansion foam into thecompartment should not be stopped, without goodreason, until the fire is extinguished. Deep seated

33Firefightillg Foam

a high-pressure hose-reel branch;

a dry powder extinguisher;

a high expansion foam generator in suctionmode. using semi-rigid ducting.

The removal of HX foam from a compartment isnot easy. Tests have been carried out using variousmethods (Reference 6) and, of these, the followinggave the best performance:

(i) Clearing/Collapsing the Foam

All of these methods have disadvantages, and theoperational situation will largely determine whichmethod is used. A high-pressure hosereel is effi-cient but will cause further water damage. A drypowder extinguisher is also extremely efficient butleaves a combined powder/water residue whichwill have to be cleaned by a salvage team. A highexpansion foam generator works well, providedthat the water residue is led away by hose and theducting is not too long but, to clear all of a com-partment, the ducting will have to be movedaround like a vacuum cleaner. This will be difficultwhere the compartment is large or where there ismachinery, stacked goods, racks etc.

One obvious point which firefighters shouldremember is that the longer the high expansionfoam is left, the easier it is to break down.Drainage from the foam weakens the bubble wallsand, in the tests using breakdown by water, it tookless water to complete the job after a 30-minutewaiting interval than after a 15-minute interval.

the compartment may contain trapped gaseswhich, with the introduction of fresh oxy-gen, could result in backdraught conditions;

open,ings, machinery, electric cables etc. willall be harder to discern, and progress musttherefore be even more careful than usual.Guide lines and communications equipmentshould always be fully used if firefightersneed to be totally immersed in HX foam.

High expansion foam, even in a relatively well-known environment, has a very claustrophobiceffect. In an unknown compartment this effect canbe heightened. Other hazards encountered are:

(g) Entering the Compartment

fires in some materials may require the maintenanceof a foam blanket for a considerable length of timebefore being completely extinguished.

All personnel entering a high expansion foamfilled compartment should wear BA, and theBA procedures should be rigorously applied.Firefighters should take in a hosereel or 45 mmhose line ready to extinguish with water any smallpockets of fire still remaining, taking care that firedoes not break out behind them.

(h) Hazards in High Expansion Foam -Safety of Personnel

penetration of light from torches and equip-ment is severely affected;

there is a general loss in effectiveness ofvision, hearing and sense of direction, i.e.disorientation;

audibility of speech, evacuation signals,low-pressure warning whistles and distresssignal units is also severely restricted;

transmission of heat is reduced and the loca-tion and travel of fire are therefore harder todetermine. Thermal image cameras are alsoineffective. Damage to structural featuresabove and around may not be visible, withthe danger of ceilings etc. collapsing ontofirefighters;

Fire Service Manual

One of the factors that shouldbe assessed is where thecompartment can be safelyventilated. Due regard should begiven to the risks of Ilashoverand backdraught when ventinga fire (see Fire Service lVlanualVolume 2 - COmlJartment Firesand Tactical Ventilation).

Should conditions be safe to do so, the best placefor a vent is diametrically opposite the genera-tor(s), at the highest level. To be most effective,Jow-Ievel openings may need to be blocked andsuitable openings may need to be made at a highlevel in order to ensure that the compartment isfilled with HX foam as quickly as possible.Opening up a ceiling or roof would be ideal, but insome cases the highest available opening may beseveral feet below the top of the compartment. Tofacilitate ventilation, smoke extractors could beemployed in the openings; high expansion foamgenerators can be adapted for this purpose. Theofficer-in-charge must station crews with hand-controlled branches or hose-reels at all the ventila-tion openings to cover any fire which might appearthere. Under no circumstances should any of thiswater be injected into the compartment, however,as this would break down the foam.

32

irefighting Foam

Chapter 6 - Practical Scenarios

hap

6.1 General

In order to discuss the use of firefighting foams itis necessary to consider practical examples.

In this Section, information is given on how typicalfires may develop in a variety of practical situations,and how the fire