FOAM VS FIRE - US Forest Service · 2013-03-30 · FOAM VS FIRE Class A Foam for Wildland Fires 2nd Edition October1993 Prepared by: Foam Task Group Fire Equipment Working Team National

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A Publication of theNational WildfireCoordinating Group

Sponsored by:United StatesDepartment of Agriculture

United StatesDepartment of Interior

National Association ofState Foresters

FOAM VS FIREClass A Foam

for Wildland Fires

October 1993

Second Edition

PMS 446-1

NFES 2246

The National Wildfire Coordinating Group (NWCG) has developed thisinformation for the guidance of its member agencies and is not respon-sible for the interpretation or use of this information by anyone exceptthe member agencies. The use of trade, firm, or corporation namesin this publication is for the information and convenience of the readerand does not constitute an endorsement by the NWCG of any productor service to the exclusion of others that may be suitable.

Additional copies of this publication may be ordered from:

National Interagency Fire CenterATTN: Supply

3905 Vista AvenueBoise, ID 83705

Order NFES #2246

NWCG has been preparing a series of publications entitled "FoamApplications for Wildland & Urban Fire Management" (starting withVolume 1, No.1 in 1988). These documents are available at no charge.They are a series of interagency, international publications that containarticles on firefighting foam, its use and application, with much informationon class A foam and foam delivery systems, etc. in each issue. Tostart receiving a copy of these as they are issued, or to obtain backissues, send your name and complete mailing address to:

Publications, USDA Forest ServiceSan Dimas Technology and Development Center

444 East Bonita AvenueSan Dimas, CA 91773-3198

A Publication of theNational WildfireCoordinating Group

Sponsored by:United StatesDepartment of Agriculture

United StatesDepartment of Interior

National Association ofState Foresters

FOAM VS FIRE Class A Foam

for Wildland Fires

2nd EditionOctober1993

Prepared by:Foam Task Group

Fire Equipment Working TeamNational Wildfire Coordinating Group

In cooperation withThe Canadian Committee on Forest Fire Management

and Forest Fire Equipment Working Group

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TABLE OF CONTENTS

OBJECTIVES ................................................................................1

INTRODUCTIONHistory ................................................................................1Class A Foams...........................................................................1Advantages of Class A Foams ................................................2Disadvantages of Class A Foams ...........................................2

FOAM CHARACTERISTICS AND PROPERTIESFoam Concentrate, Solution, and Foam.................................2Foam Properties .........................................................................2

Expansion .........................................................................2Density ..............................................................................2Drainage/Drain Time .......................................................2Surface Tension...............................................................3

Foam Type ................................................................................3Mix Ratio—What Concentation Should Be Used? ................3Foam's Action on the Fire Triangle ........................................4

PERSONAL SAFETYPersonal Safety and Protection ...............................................5Working Conditions ....................................................................6

ENVIRONMENTAL CONCERNSSoils/Vegetation ..........................................................................6Water Supply ..............................................................................6

FOAM SYSTEMSStorage ................................................................................7Proportioning ...............................................................................7Manual Regulation .....................................................................9

Batch Mixing ....................................................................9Suction-side Regulator ....................................................9Eductor ..............................................................................9Around-the-pump Proportioner .....................................10

Automatic Regulation ...............................................................10Balanced-Pressure Bladder Tank Proportioner .........10Balanced-Pressure Pump Proportioner.......................10Direct Injection Proportioner ........................................11

Aerial Suppression Proportioner System ..............................11General Requirements for Aerial Proportioner ..........11Operational Requirements for Aerial Proportioner ....12

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Foam Generation......................................................................12Nozzles ...........................................................................14

Conventional Nozzles .........................................14Aspirating Nozzles ..............................................14Compressed Air Foam Systems (CAFS) ........14Aerial Delivery .....................................................16

Equipment Maintenance and Housekeeping ........................16

APPLICATIONBasic Considerations ...............................................................17Prescribed Fire .........................................................................17

OPERATING GUIDELINESFoam Delivery Systems ..........................................................18

Aspirating Nozzles .........................................................19CAFS ..............................................................................19Aerial Generating systems ...........................................19

SUPPRESSIONInitial Attack ..............................................................................19

Direct ..............................................................................19Indirect ............................................................................20

Structure Protection .................................................................20Mop-up ..............................................................................20

Back-pack Pumps ..........................................................21

SUMMARY ..............................................................................21

CLASSIFICATION SYSTEM FOR APPLICATION OFWILDLAND FIREFIGHTING FOAMS ...............................................23

GLOSSARY OF TERMS....................................................................25

SOURCES OF INFORMATION .........................................................28

METRIC SYSTEM AND EQUIVALENTS .........................................29

APPROXIMATE CONVERSION TABLES .......................................30

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OBJECTIVESThis publication covers the basics of using classA foams and discusses their adaptability topresent application equipment. Its purposes areto provide:

1. Basic understanding of how class A foamswork and how they can be used.

2. Knowledge for firefighters of the concepts pres-ently being used in foam application equipment.

3. Information needed to achieve the most effi-cient use of class A foam.

NOTE:This document is one of a series of three"Foam vs Fire" publications that are avail-able. These are:

1. Primer2. Class A Foam for Wildland Fires3. Aerial Applications

(to be published in 1994/95)

INTRODUCTIONHistoryWater has always been the mainstay for fire sup-pression for both wildland and structural fires.The water bucket gave way to the backpack pump,which in turn gave way to the portable pump andhose system in the early 1920’s. The advent ofdependable mechanized vehicles resulted in achange from horse-drawn to motorized firefightingunits—except in mountainous areas where ac-cessibility was difficult.

In the 1930’s and 1940’s foams were evaluatedin studies aimed at improving the fire-extinguish-ing capabilities of water. A number of additiveswere identified that improved the knock-down char-acteristics of water. They also decreased thetendency of fires to rekindle.

Fire engines and aircraft were used in evaluat-ing water, chemicals, equipment, and suppres-sion techniques during Operation Firestop in 1954.The many positive results paved the way for anumber of new tools in wildland fire suppres-sion, including use of chemicals and aircraft.

By 1968 the use of foam to fight forest fires hadbeen investigated numerous times but—due topoor performance, specialized equipment needs,and the low level of interest—no concerted in-vestigative or developmental work was undertaken.

Recent developments in foam technology cre-ated a renewed interest in foam as a wildlandfirefighting tool. The first was the developmentand use of compressed air foam systems (CAFS).In these systems, foam is generated by injectingcompressed air into a solution of water and foam-ing agent as it is pumped through a hose.Although CAFS increased the usefulness of lim-ited water supplies, it did not alleviate the prob-lem of carrying large quantities of foaming agent,since commercially available foaming agentsrequired mix ratios of 3 to 6 percent (3 to 6 gal-lons of foam concentrate for every 100 gallonsof water).

The second development was the introduction ofa new family of synthetic hydrocarbon surfactantfoaming agents. This foam was developed andintroduced in Canada in 1985. The recommendedmix for foam solutions of this concentrate is lessthan 1.0 percent, depending on fuel and fire char-acteristics and the generating/application methodbeing used, reducing the amount of the concen-trate needed.

Several foam concentrates of this type are com-mercially available. They are being used by mostevery wildland fire management agency and manymunicipalities responsible for wildland fire sup-pression in the United States and Canada. Thesefoams are being applied from both ground equip-ment and aerially in a variety of suppression sce-narios.

Class A FoamsClass A foam is a mechanically generated ag-gregation of bubbles having a lower density thanwater. The foam is made by introducing air intoa mixture of water and foam concentrate.

The bubbles adhere to the wild-land fuels (or other class Afuels) and graduallyreleaset h e

mois-ture they

contain. The bub-bly water absorbs heat

more efficiently than unbubbledwater, and the bubble mass provides

2

a barrier to oxygen, necessary to sustain com-bustion. The reduced rate of water release resultsin more efficient conversion of water to steam,providing enhanced cooling effects and, alongwith the surfactants contained in the solution,allows the water to penetrate the fuels and reachdeep-seated fire sites. The bubble mass alsoprovides a protective barrier for unburned, ex-posed fuels.

Although class A foam contains wetting agentsthat reduce the surface tension of the containedwater, it should not be confused with the wettingagents which are used exclusively for improvingthe penetration of water into deep-seated firesin class A fuels. In fact, these wetting agentsare commonly formulated to prevent foaming.

The ratio of class A foam concentrate to wateris typically 0.1 to 1.0 percent. Class A foam canbe produced using numerous types and configu-rations of equipment, which are discussed laterin some detail.

Advantages of Class A Foam

• Increase the effectiveness of water• Extend the useful life of water• Provide short-term fire barrier• Effective on fire in all types of class A fuels• Reduce suppression and mop-up time• Relatively easy to use (mixing and handling)• Visible from ground and air.

Disadvantages of Class A Foam

• Can be irritating to the skin and eyes• Corrosive to some metals and may speed

deterioration of some types of seal material• May have harmful environmental effect as

a result of exposure to high concentrations• Reduced life expectancy of leather goods such as footwear.

FOAM CHARACTERISTICS ANDPROPERTIES

Foam Concentrate, Solution, and FoamFoam concentrates are liquids that contain foamingand wetting agents as well as small amounts ofother chemicals to inhibit corrosion, to stabilizethe foam, and to maintain the homogeneity ofthe liquid. Although the composition of the variousfoam concentrates are similar, they are not iden-tical and should be handled and stored sepa-rately.

Foam concentrates are added to water (in amountsprescribed by the manufacturer) to produce foamsolution which, when aerated, produces foam.Foam is a relatively stable mass of small bubblesmade by forcing large quantities of air into a smallquantity of water containing the foam concen-trate. Class A foams are designed specificallyfor fighting fires in class A fuels.

Foam PropertiesExpansion

Expansion is the increase in volume of a solu-tion, resulting from the introduction of air. It isa characteristic of the specific foam concentratebeing used, the mix ratio of the solution, the ageof the concentrate, and the method of producingthe foam. Different generators such as CAFS(compressed air foam systems) or aspiratingnozzles produce foams having different expan-sion factors using the same foam solution.

A 10 to 1 (10:1) expansion of a 1-percent so-lution creates a foam that is 90 percent air, 9.9percent water, and only 0.1 percent foam con-centrate. The net result is a foam that is muchlighter than water given the same volume.

Expansion ratios are divided into three classesrelated to how much foam is generated.

Low expansion 1:1 to 20:1Medium expansion 21:1 to 200:1High expansion 201:1 to 1000:1

Expansion is one of several characteristics thatshould be considered in tailoring a foam for aspecific task.

DensityThe density of a foam is its weight per unit vol-ume. It affects how well a foam projects whendelivered from a nozzle and the resistance tothe effects of wind. A low expansion (relativelylittle air, and thus heavier) foam has a higherdensity and more resistance to deflection by thewind than a medium or high expansion (mostlyair, with a little foam solution, and thus lighter)foam.

Drainage/Drain TimeThe stability of the bubble mass is measured bythe rate at which the foam releases the solutionfrom within its bubble structure. This process,known as drainage, is a measure of the foam’seffective life. The use of cold water tends todecrease the rate of drainage, while the use of

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DRAINAGE DIFFERENCES

hard or saline water produces a much faster drain-ing foam. Fast drainage also occurs when foamconcentrates are used in combination with long-term retardants (which contain salts) to enhancethe retardant’s spreading and coating character-istics.

Drain time indicates how quickly the foam re-leases the foam solution from the bubble mass.Once the solution is released, it becomes avail-able for wetting of fuels or it may run off the fuel.Foams with short drain times provide solution forrapid wetting. Foams with long drain times holdsolution in an insulating layer for relatively longperiods of time prior to releasing it.

Surface TensionThe foaming agent component of the foam con-centrate facilitates the formation of bubbles andthe stabilizer imparts the strength to the bubbleskins to maintain this structure. The wetting agent(surfactant) reduces the surface tension of theliquid so that the fluid can spread more readily,but more importantly, penetrate deeper into or-ganic fuels at a faster rate.

Foam TypeFoam type is a term used to describe the con-sistency of foam as the combination of drain timeand expansion ratio (for low expansion foam).Foam type is important to understanding how thefoam will perform. A foam with a fast drain timeand a 5:1 expansion ratio performs differentlythan a foam with a slow drain time and a 15:1ratio. The foam types you will use are as fol-lows:

Expansion Drainage1:1 FOAM SOLUTION Rapid

- A clear to milky fluid- Lacks bubble structure- Mostly water

WET FOAM- Watery- Large to small bubbles- Lacks body- Fast drain times

FLUID FOAM- Similar to watery shaving cream- Medium to small bubbles- Flows easily- Moderate drain times

DRY FOAM- Similar to shaving cream- Medium to small bubbles- Mostly air- Clings to vertical surfaces

20:1 - Slow drain times Slow

A dry foam holds its shape, adheres well, andreleases its solution slowly, creating a better in-sulating blanket than a wet foam which flows,drips, and releases its solution quickly. Fluidfoam releases the solution more rapidly than adry foam but holds its shape and adheres betterthan a wet foam. Fluid foam may be better atcooling and wetting than dry foam. Foam solu-tion is a slightly frothy fluid that may be the choicewhen rapid penetration of liquid is necessary suchas deep-seated fires and smoldering snags.

As you can see, many types of foam can bemade, and each type is best suited for a specificapplication. Different foam types are producedby altering the amounts of air and/or foam con-centrate used to produce the foam.

Mix Ratio—What ConcentrationShould Be Used?The user’s specific needs and objectives mustbe identified before determination of a suitablemix ratio. Since each foam generating systemproduces a unique foam for a given mix ratio,the foam can be tailored to the specific need. Ifthe need is to protect tree crowns, a fairly dryfoam—slow-draining and adherent—should beused. For the pretreatment of the perimeter ofa prescribed burn area, a slow-draining to mod-erately rapid-draining foam is required; otherwise,the drainage should be fast enough to providegeneral wetting. Each manufacturer suggestsconcentrations to be used for a range of needs.However, since numerous factors (such as waterhardness and temperature, the generating sys-tem being used, etc.) affect the type of foamproduced, these suggestions should only beconsidered as a starting point. Matching foam

➤➤ ➤➤➤

➤➤➤➤ ➤

➤➤ ➤➤➤

➤➤➤➤ ➤

100

80

60

40

20

00 5 10 15 20 25

LAPSED TIME (Min)

DR

AIN

ED

%

Simulated sea water (4.9x)

Fresh water (4.9x)

DRAINAGE DIFFERENCES

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OXYGENOXYGEN

SMOKEHydrogen Cyanide

FLAMEFlammable Vapor

Water Vapor

Carbon Dioxide

Carbon Monoxide

Carbon Particles

Sulfur DioxideOther Gases

With a foam application, the fuel component isblanketed with an opaque layer whose reflectivequalities intercept radiant energy and inhibit re-kindling. The insulating characteristics of thislayer also prevent heat from escaping and pre-heating other fuel particles. The foam separatesthe surface of the burning fuel from oxygen inthe air. Vapor suppression occurs by trappingflammable vapors at the fuel interface. The foamblanket varies in depth and stability, dependingon mix ratio and the foam generation process.The foam also acts as a heat sink by absorbingthe heat generated by the combustion processand using this energy to evaporate the water con-tained in the foam rather than to propagate thefire.

The foam clings to all types of fuels on appli-cation and releases water slowly over time. Thebenefit of the available water is maximized whenthe foam holds the moisture where it is mostneeded until it can be absorbed. In addition, thesolution that is released contains wetting agentswhich facilitate the water’s spread over a largearea, allow it to adhere to the fuel surface, andimpart greater penetrating ability.

The moisture content of the treated fuel is in-creased due to the foam solution’s enhancedwetting qualities. Consequently the heat absorp-tion potential of foam-treated fuels is increased.Water in the foam state adheres to fuel surfacesin substantially greater quantities without runningoff and is available to continue wetting the fuelover a prolonged period of time. This results ina longer time span of effectiveness for a givenapplication. The liquid that is vaporized at thehot fuel’s surface cannot readily escape due tothe overlying bubble mass and, therefore, remainsat the surface to enhance extinguishment.

Foam descending through aerial fuels envelopsthe fuels it encounters, resulting in the isolationof combustible gases. The draining foam sets

generated with the firefighting needs increasesthe effectiveness of the water being applied, anddecreases the effort necessary to complete thejob.

Foam's Action on the Fire TriangleThe statement “fire doesn’t like water much” isas valid today as on the day it was coined.However, by converting water from a liquid stateto a bubble state, new characteristics are im-parted to the water to give it superior suppres-sion qualities. This bubble mass, known as foam,is a fire suppressant because it relies on themoisture that it contains to be effective. Thestructure of the foam can range from a rigid toa relatively fluid aggregation of bubbles.

The combustion process is commonly depictedas a fire triangle. Each side of the triangle containsone of the components required to sustain fire:Heat, oxygen, and fuel. Suppression of a wild-land fire, as with any fire, depends on breakingone or more of the sides of the fire triangle. Foamcan be an effective tool for breaking each of theselinks.

Water, possessing the enhanced characteristicsimparted by the foam concentrate, becomes muchmore efficient in breaking the fire triangle by at-tacking all three sides, although to different de-grees.

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������������������������������������

FUEL

OXY

GEN

������������������������������������

FUEL

OXY

GEN HEATFIRE

������������������������

FUEL

Smothers CoolsPenetratesSmothers

Isolate

CoolsPenetrates

5

up a “drizzle,” which dilutes these volatile sub-stances to a level where the temperature requiredfor combustion is greatly elevated at the fuel/airinterface. The buoyancy of the descending bubblemass causes the foam to penetrate better throughaerial fuel complexes and to envelop fuels thatmight not otherwise be wetted.

Vertical surfaces are difficult to wet with watereven if they are receptive to it; but, in the foamstate, a substantially greater amount of water canbe held on the fuel surface and made availablefor wetting of these surfaces as well as for heatabsorption and dissipation. Hard to wet surfaces(such as green foliage) shed water, but foamadheres to them and wets these surfaces via thewetting agent.

If isolation rather than wetting is the prime need,a dry foam can be produced which remains rigidand does not flow when applied to vertical sur-faces.

The variations in forest fuel complexes requireadjusting the foam type to meet specific sup-pression objectives: A dry foam coats and adhereswell and drains and wets at a slow rate; a fluidfoam flows to some degree upon coming to restand drains readily; and wet foam flows readily,and dissipates and penetrates rapidly.

Visibility of the foam aids in the conservation ofoften scarce water. The ability to see the foamavoids waste of water from over-treatment andpinpoints where the foam is breaking down sothat the control line can be reinforced as needed.The foam mass is visible enough to permit tyingaerial foam drops together.

PERSONAL SAFETYPersonal Safety and ProtectionFoam concentrates are similar to common house-hold detergents and shampoos. Fire suppres-sant foams, diluted for use in fire fighting, aremore than 99 percent water. The remaining 1percent contains surfactants (wetting agents),foaming agents, corrosion inhibitors, and dispers-ants.

Approved fire suppressant foam concentrates andsolutions have all been tested and meet specificminimum requirements with regard to mamma-lian toxicity:

Acute oral toxicityAcute dermal toxicityPrimary skin irritationPrimary eye irritation

As with any chemical substance, a small per-centage of the population may be allergic to orhave an unusual sensitivity to a specific productthat will not be detected during testing.

Foam concentrates are strong detergents. Theycan be extremely drying and exposure to the skinmay cause mild to severe chapping. This canbe alleviated with the application of a topical creamor lotion to the exposed areas.

All of the currently approved foam concentratesare mildly to severely irritating to the eyes. Anyoneinvolved with or working in the vicinity of foamconcentrates should use protective splash goggles.Rubbing the eyes or face may result in injury tothe eyes if hands have become contaminatedwith the concentrate during handling.

There is no evidence to suggest that foams ortheir constituents have any carcinogenic, repro-ductive, or mutagenic effects.

All personnel involved in handling, mixing, andapplying foam concentrates or solutions shouldbe trained in proper procedures to protect boththeir health and safety as well as that of theenvironment.

All containers of foam concentrate or solutions,including backpack pumps and engine tanks,should be labeled to alert personnel that they donot contain plain water, and that the contentsMUST NOT be used for drinking purposes. If afoam concentrate is ingested, the individual shouldseek medical attention as soon as possible.

Fluid Foam

Wet Foam

DryFoam

Wet Foam

Fluid Foam

Dry Foam

6

All personnel MUST follow the manufacturer’s rec-ommendations as found on the product label andproduct material safety data sheet (MSDS). Toeliminate possible health problems from prolongedexposure to the skin and eye the following pre-cautions should be taken:

1. When handling concentrates, goggles, water-proof gloves (rubber or plastic), and disposablecoveralls should be worn. Leather boots shouldnot be worn at the mixing site, since foam con-centrate rapidly penetrates leather, resulting inwet, soapy feet.

2. Clothing soaked with foam concentrate shouldbe removed and thoroughly rinsed with water.

3. Eyes splashed with foam concentrate or afoam solution should be flushed as soon aspossible with large amounts of clean water forat least 15 minutes.

4. If skin contact occurs, wash off with water,and remove contaminated clothing.

5. A non-allergenic lotion/hand cream should beused to avoid raw chapping of skin.

6. Inhalation of foam vapors can be irritating tothe upper respiratory tract, and should be avoided.

7. Ingestion of foam concentrate or, to a lesserdegree, the solution can be harmful.

Working ConditionsSlipperiness is a major hazard at storage areasand unloading and mixing sites. Because foamconcentrates and solutions contribute to slipperyconditions, all spills MUST be cleaned up imme-diately.

Spills of foam concentrate can be covered withsand or absorbent material and then removedwith a shovel. Do not apply water directly to thespill area. Foaming and possible contaminationto the surrounding area may result.

Spills MUST NOT be flushed into drainage ditchesor storm drains. Do NOT flush equipment neardomestic or natural water supplies, creeks/riv-ers, or other bodies of water. If a large spilloccurs or concentrate enters a water supply,contact your local authorities immediately. Beprepared to provide them with the appropriatemanufacturer’s information.

Care should be taken during planning that per-sonnel applying foam from the ground are ableto stand in untreated areas as they proceed. Step-ping onto a foam blanket which conceals objectsor holes can be dangerous.

ENVIRONMENTAL CONCERNSSoils/VegetationWhen the foam is applied in the forest, its com-ponents will inevitably contact the soil. Surfac-tant absorption is dependant on many factors,including silt and clay content, organic matter,and surface area.

Generally, foams have a minimal effect on forestsoils, as the approved foam products are biode-gradable and have minimal adverse environmentalimpact.

Water SupplyDue to the sensitivity of aquatic habitats, theapplication of foam directly into bodies of waterMUST be avoided.

7

The foam concentrates have varied toxicities withrespect to fish but when used in a diluted formfor application, they are generally presumed tobe non-toxic.

Follow these guidelines to reduce possible im-pacts to the environment:

• Inform all personnel using foam of the po-tential problems that can be caused byfoams in water bodies.

• Locate foam mixing and loading areas to mini-mize contact with natural bodies of water.

• Exercise care to avoid spills at mixing,loading, and application areas—especiallynear live streams.

• Exercise particular caution when usingfoams in watersheds where fish hatcher-ies are located.

• Avoid direct application or drops into riv-ers, streams, lakes, or lake shores. Usealternate methods of line building or ter-minate the use of foam altogether.

• Notify authorities promptly of any fish killor spill into a water body.

• Include precautionary measures in train-ing for fire personnel.

• Foam residues might be a problem whendipping from rivers or lakes with a helicop-ter because of threatened and endangeredspecies. Helicopter managers need to beaware of local conditions and guidelinesregarding dipping from streams and lakes.

When foams are used near domestic reservoirsand domestic water supplies, the same precau-tions MUST be exercised. Leave at least a 100-to 200-foot buffer zone from the high-water line.Under normal conditions, plants and soil canabsorb a majority of the foam solution before itwashes or leaches into the water body.

Foam components undergo chemical and biologi-cal degradation processes that reduce the envi-ronmental effects. Biodegradation varies from14 to 30 days, depending on the product beingused.

FOAM SYSTEMSStorageAll of the approved class A foam concentrateshave been evaluated on the basis of their abilityto (a) maintain their performance characteristicsand (b) produce foam, after storage for 1 year,that is similar in quality to that produced fromfresh concentrate.

Each foam concentrate supplier includes properstorage information on the product label. In gen-eral, suppliers do not recommend storing belowfreezing or above about 100 °F. In situationswhere the concentrate may be required for im-mediate use, the minimum storage temperatureshould be well above freezing. The viscosity ofthe foam concentrate increases significantly atlow temperatures. This results in slow flow ofthe concentrate and proportioning devices thatmay not function accurately, if at all.

Storage in the original shipping containers is rec-ommended, although other polyethylene orpolypropylene containers may be used. Storagein metal containers may cause product degrada-tion. Foam solutions should not be stored anylonger than necessary. Water impurities and metaltank parts in contact with the solution may dras-tically alter foaming characteristics.

ProportioningThe first step in creating foam is adding the re-quired amount of foam concentrate to water tocreate foam solution. This process, known asproportioning, is used to proportion foam con-centrate into water streams for use with stan-dard nozzles, aspirating nozzles, or in compressedair foam systems (CAFS). There are two basictypes of foam concentrate proportioning systems,manually regulated, and automatic regulating. Theproportioning system chosen is independent ofnozzle or foam generating device used.

Every device exposes some hardware to thecleansing, and penetrating qualities of class Afoam. When foam concentrate dries, it can plug

8

Proportioners*ADVANTAGES 1 2 3 4 5 6 7Maintain desired mix ratio despite changes in water flow and pressure X X XUnlimited hose length X X X X X XUnlimited number of hose lines X X X X X XEasily adjusted mix ratios X X X X XNo moving parts X X X X XNo loss in water flow or pressure X X XRequires no equipment investment X

DISADVANTAGESTank and pump corrosion X X XPlumbing corrosion X X X X X X XPump priming X X XPump cavitation X X XWater tank refill fluid level obscured X X XInconsistent dispersion of concentrate XFoam solution degradation XExcessive foam concentrate use X X XClean water supply contamination X X XRemoves lubricants X X X X X X XCleaning required after every use X X X X X X XSpecific water flow requirements XSpecific pressure requirements XVertically mounted attitude only XLimited nozzle elevation XDependent on pump vacuum XConcentrate viscosity sensitive X X X XConcentrate resupply interrupts concentrate input XRequires auxiliary power X X

Accurate Water flow range• Any flow, single mix ratio X• Single flow, single mix ratio X X X• Any flow, any mix ratio (between 0.1

and 1.0 percent for class A foam) X X X

Initial Equipment Investment• $ 0 - $ 500 X X X X• $ 500 - $ 1,000• $ 1,000 - $ 2,000 X• $ 2,000 - $ 4,000 X• $ 4,000 - $ 6,000 X

*Key to Proportioning Devices 1 Batch Mixing

2 Suction-side Regulator3 In-line Proportioning System (Eductor)4 Around-the-pump Proportioning System

5 Balanced Pressure Bladder Tank Proportioning System6 Balanced Pressure Pump Proportioning System

7 Direct Injection Proportioning System

Table 1.Advantages and Limitations of Proportioning Devices

9

small tubing and orifices found on theseproportioners. Flushing, rinsing, lubrication, andgeneral good housekeeping are necessary foreach of these devices. Advantages and disad-vantages of each type are listed in table 1.

Manual RegulationManual regulation systems, which must be moni-tored and changed manually,are frequently used—although less precise regulation of concentrateaddition, and the resulting foam quality, is usu-ally achieved.

Batch MixingThe simplest method of making a foam solution isto manually add foam concentrate to the watersupply. This method, called batch mixing, is con-venient for conventional water pumping systems.A measured volume of concentrate is poured intoa measured volume of water to yield a foam solutionof the recommended strength. Batching is poten-tially wasteful because the required volumes of bothwater and concentrate must be estimated, espe-cially when refilling a partially full tank.

The concentrate should be added to water, be-cause adding water to the foam concentrate causesexcessive foaming in the tank as the water is added.Since the foam concentrate is heavier than water,mixing or recirculation of the concentrate/water mix-ture is required to obtain a homogeneous solution.The solution should be used as soon as possiblefor optimum performance.

Despite a number of limitations, batch mixing isa common proportioning method for engines,portable tanks, bladders, and extinguishers.

Suction-side RegulatorThe suction-side regulator uses water pump vacuumto add foam concentrate, via an in-line tee andregulating value, to the water stream on the inletside of the pump. At specific flow conditions theregulator is proportional. However, the in-line teehas no influence on vacuum, so the regulator cannot maintain a given mix ratio as water flow changeswithout a manual adjustment.

Because the regulator sends concentrate throughthe pump and the tank, when recirculating, itslimitations are similar to those of batch mixing.

EductorThe eductor (or in-line proportioning system) draftsfoam concentrate from a container to the pres-sure side of the water stream using venturi ac-

tion. As pressurized water flows through the ven-turi, an area of negative pressure is created atthe venturi throat. Atmospheric pressure forcesthe foam concentrate into the negative pressurearea of the eductor.

Eductors work on any pump that can generatea pressure of 200 psi. They are usually propor-tional at one water flow rate. Because they aredesigned to operate within specific concentra-tion ranges, a different eductor may be requiredto operate at a concentration outside that range.In some cases diluting the concentrate may allowuse of the eductor at hand.

Eductors eliminate many of the problems asso-ciated with concentrate exposure to pump andtank. They also make possible accurate propor-tioning while the tank is refilled or while the pumpis fed from a hydrant.

SUCTION SIDE REGULATOR

Suction Side

Regulator

Pump

FoamSolution

Shut-off Valve

Chaeck Valve

Metering Valve

FoamConcentrate

Water Suction

Line

Foam Solution

Discharge

Check Valve

Water

Pump

Eductor

Check Valve

Metering Valve

FoamSolution

Discharge

FoamConcentrate

IN-LINE PROPORTIONER (EDUCTOR)

WaterSuction

Line

10

Eductors are most appropriate for applicationsof constant water flow near the pump.

Around-the-pump ProportionerThe around-the-pump proportioner diverts a por-tion of the pump discharge through an in-lineproportioner back to the suction side of the pump.This loop around the pump is used to draw con-centrate up through the venturi and into the mainwater stream.

The around-the-pump system works on portableor built-in pumps of any size or output. Watertank refilling and pump nursing do not affect thissystem’s performance. Around-the-pump devicesare manually regulating because the venturi hasto be adjusted when the water flow changes. Theadjustment is done manually. When water flowhas stopped, the shut-off valve at the venturiMUST be turned off to prevent more foam con-centrate from being drawn into the water line.

The around-the-pump proportioner is more flex-ible than the eductor, but it introduces concen-trate to the pump and tank in the same way asthe suction-side regulator. Therefore, the samecorrosion, cleansing, cavitation, and other relatedproblems also limit the around-the-pump-proportioner.

Automatic RegulationAutomatic regulation devices are designed tominimize the limitations of the previously discussedmethods. Specifically, they proportion accuratelyover wide ranges of water flow or pressure, ad-justing automatically to changes in water flowand pressure to maintain the desired mix ratio.Foam concentrate is added on the discharge sideof the pump to avoid tank and pump problems.

The mix ratio can be quickly changed during op-eration. These devices place no restrictions onhose length or number of hoselays.

Balanced-Pressure BladderTank Proportioner

The balanced-pressure bladder tank system usesa small diversion of water to pressurize a blad-der containing foam concentrate. The concen-trate passes through a metering valve before itenters the water stream on the low pressure sideof a pressure differential valve or venturi.

Concentrate is added according to the differencein pressure at the differential valve. As waterflow increases and the difference in pressure in-creases, foam concentrate flow is able to increaseproportionally.

The bladder tank proportioner has no moving parts.It can be portable or plumbed integrally. Foamconcentrate must be transferred to the bladderfor storage and dispensing. When the bladderis being filled, concentrate flow is interrupted.

Balanced-Pressure Pump

ProportionerThe balanced-pressure pump system senses waterpressure with a pilot-operated relief valve. Apump delivers concentrate to a venturi in the waterline according to the pressure at the relief valve.A metering valve allows for selection or changeof the desired mix ratio.

BALANCED PRESSURE BLADDDER TANK PROPORTIONER

Three-WaySelector Valve

WaterDumpLine

Check Valve

Metering Valve

PressureDifferential

ValvePump

Water

FoamConcentrate

PressureTankwith

Bladder

H2O

H2O

FoamSolution

DischargeWaterSuction

Line

FoamConcentrator

LoadingLine

AROUND THE PUMP PROPORTIONER

Eductor

Pump

Shut-Off Valve

Shut-Off Valve

Check Valve

Metering Valve

FoamConcentrate

WaterSuction

Line

FoamSolution

Discharge

11

BALANCED PRESSURE PUMPPROPORTIONER

FoamConcentrate

WaterSuction

Line

Pilot-OperatedRelief Valve

Water

CheckValve

ConcentratePump

Metering Valve

Check Valve

FoamSuction

DischargeModifiedVenturiDevice

Pump

If the relief valve senses 150 psi of water pres-sure, then it will ensure that 150 psi of foamconcentrate pressure flows from the foam pumpto the venturi. Concentrate enters the waterstream in proportion to the pressure differentialacross the venturi. Excess foam concentrate isrelieved to the concentrate tank.

Refilling the concentrate tank does not interruptconcentrate flow. Concentrate flow is depen-dent on an auxiliary powered pump.

Direct Injection ProportionerThe direct injection proportioner adds concen-trate based on measured water flow. An in-lineflow sensor determines water flow past the pump.A micro-processor receives electronic signals ofmix ratio from the control panel and water flowfrom the flow sensor. The processor then com-mands a pump to deliver concentrate at a pro-portional rate.

This proportioner is capable of providing morethan one foam concentrate when more than onestorage container is linked to the pump. Thepump runs only on demand.

Aerial Suppression Proportioning SystemThe proportioning system used to produce foamsolution in airtankers and helitankers injects thefoam concentrate into water in the tank or bucketusing a pump and timer system triggered by thepilot. Circulating systems have been devisedfor some helibuckets but in all other instancesdispersion of the foam concentate depends oninjection pressure and the often minimal agita-tion occurring during flight.

The consistent foam injection rate combined withcareful calibration provides an accurate methodof proportioning that is straightforward and re-liable.

Call-when-needed (CWN) contracts permit heli-copter contractors to furnish equipment for dis-pensing foam and retardant concentrates intobuckets. Since the equipment is relatively new,detailed design or performance specifications arenot yet available. Thus, until specifications aredeveloped, the evaluation criteria presented herecan be used —along with good judgement.

General Requirementsfor Aerial Proportioner

Compatibility of Materials: The materials usedin construction of any foam dispensing unit mustbe compatible with all foams, and resistant tocorrosion, erosion, etching, or softening. Toevaluate the materials, submerge a sample infoam concentrate for 96 hours, then in a 1-1/2percent solution for 96 hours. Any change in-dicates that the material must not be used.

Installation: Installation of the unit must not re-quire any major or permanent modifications tothe helicopter.

Restraint: The foam pumping unit containmentvessel and concentrate must be affixed to thehelicopter in a way to prevent injury to person-nel or damage to the helicopter. The designmust meet the ultimate inertia forces specifiedin FAR 23.56 1(b)(2). All parts of the foampumping unit must be designed so that at allpoints of contact with the helicopter, no abra-sion or damage occurs to the helicopter.

ELECTONICALLY CONTROLLED PROPORTIONEER

FlowTotalizer

MeteringValveMicroprocessor

Box

Shut-Off Valve

ConcentratePump

CheckValve

CheckValve

FlowMeter

Water Water

Pump

WaterSuction

Line

FoamConcentrate

FoamSolution

Discharge

DIRECT INJECTIONPROPORTIONER

12

Location of Unit: The preferred mounting loca-tion of the foam pumping unit and containmentvessel is external to the helicopter, perhapsattached to or within the water supply.

Routing of Hose: The hose used to carry theconcentrate must be routed out the side of thehelicopter away from the pilot. Hoses must berouted in a manner that will not interfere withflight controls.

Breakaway Fittings: Any hose must have a dis-connect that will pull away from the hose whenthe bucket is released. The disconnect must beclose to the helicopter to keep the hose frombeating against the helicopter. The helicopterside of the disconnect must be able to hold thefluid pressure in the line, and be able to be pulledapart at one-third the buckets empty weight. Thelower part of the hose must be securely attachedat the bucket such that, if the bucket is released,a sufficient load is applied to the disconnect torelease it.

Containment: Any unit mounted inside the he-licopter (other than those that have STC's or337's), must have a containment vessel aroundthe pumping unit and concentrate storage sup-ply. The containment vessel must be able tohold 125 percent of the concentrate supply. Evenin moderate turbulence, the containment vesselmust be able to contain the foam concentrate.The discharge hose and fittings must have acontainment sleeve of clear hose so that leakswill be visible.

Size: The unit must be small enough to easilyfit into or onto the helicopter.

Weight: The foam dispensing system emptyweight shall not exceed 50 pounds.

Maintenance: The foam dispensing system isexpected to require no major maintenance dur-ing each fire season.

Foam Quantity: The unit shall carry a minimumof 5 gallons of concentrate for each 100 gallonsof bucket capacity.

Power to Operate: Power source for the dis-penser must be obtained from the helicopter byinstalling a MS 3116F-12-3P, three-pin connec-tor on the cord to the unit. Pin A shall be +28vdc and pin B for ground. (This is the same plugused for the infrared imaging system.)

Vibration: The unit must be designed and con-structed so as to be damaged or fail due to vi-bration or shock loading when installed in thehelicopter. The unit must not cause undue vibra-tion in the helicopter during operation or in flight.The unit must be designed and installed so asnot to cause any concentrated stress on the he-licopter.

Operational Requirementsfor Aerial Proportioner

Operation: The pilot of the aircraft must be ableto operate the unit with a minimal level of atten-tion so as not to interfere with normal flying ofthe aircraft. An automatic system would be pre-ferred. Under no circumstances can any phaseor aspect of the foam dispensing system impairthe flight safety of the aircraft. Once the controlis set for flow rate, there should be no adjust-ment necessary to the unit.

Flow Rate: The system must be capable of dis-pensing a variable amount of concentrate, in flight,to achieve a mixture ratio ranging from 0.1 to1.0 percent by volume, in 0.05 percent incre-ments. (Example: for a water bucket load of 250gallons, a mixture ratio of 0.5 percent wouldrequire 1.25 gallons of injected concentrate; thenext selected increment of 0.6 percent wouldrequire 1.375 gallons of injected concentrate.)

Concentrate Loading: Loading of 5-gallon con-tainers is preferred. If bulk loading is to be used,a system must be employed such that any spill-age of the concentrate will not come into contactwith the helicopter. Servicing must be accom-plished during normal refueling time for the he-licopter and take no longer than the refuelingoperation. (Reference publication 9257 1201—SDTDC, August 1992, Field Survey of HelicopterFoam Injection Systems.)

Foam GenerationFoam is made by mechanically adding air to thefoam solution. Class A foams can be made withaspirating nozzles, compressed air foam systems,and by dropping foam solution through the air.Conventional water nozzles deliver an effectivefoam solution (wet water). All of the foam gen-erating equipment devices have a role in fire sup-pression. A summary of the advantages anddisadvantages of each is given in table 2.

13

ADVANTAGES DISADVANTAGES

Conventional Can use existing Normal water flowNozzles equipment Limited to foam solution

More efficient use of applications onlycommon equipment Generally creates only froth

Low Expansion Makes foam Needs a high ratio ofAspirating Requires minimal concentrate to waterNozzle equipment Needs a high working pressure

Simple to operate to develop foamSimplest and initially Needs high water flows the cheapest generating Incomplete conversion of water device to foam

Limited foam variabilityLimited discharge distanceSame hydraulics as waterLess viable foam

`Medium Creates excellent ground High water flowExpansion fire break Requires more concentrateAspirating Easy to operate Poor discharge distanceNozzle Obscures ground footing

CAFS Requires less water More mechanical componentsGreater discharge Slug flow distance High initial costComplete conversion of More complex operation water to foam Deceiving energy stored inRequires less concentrate hose is a safety hazardRope effectCan produce all foam typesLight hose weightReduced head pressureStored energy in hoseMost stable foam

Aerial Delivery Uses conventional drop Limited control of final product systems

Table 2.Summary of the Advantages and Disadvantages of Foam Generating Systems.

14

through the air. With the same nozzle and waterflow, foam type can be changed by adjusting themix ratio.

Aspirating nozzles require up to 1.0 percent mixratio; usually 0.5 for low expansion nozzles and0.7 for medium expansion nozzles. Low expan-sion nozzles are made for solution flow from 5to 100 gpm with up to 20:1 expansion. Thereare relatively low-cost nozzles available for singleflow rates and more expensive adjustable nozzlesthat cover wide ranges of flow rates. Mediumexpansion nozzles are designed for flows up to100 gpm with expansion ratios from 20:1 up to200:1.

Compressed Air Foam Systems(CAFS)

Compressed air foam is a high energy foam; thatis, it adds the energy of an air compressor tothat of the water pump to create and dischargefoam. Foam generation does not cost energy,it increases the energy of the system.

A CAFS produces foam by injecting compressedair into a foam solution. Foam is generated whenfoam solution and air are mixed together due to

NozzlesConventional Nozzles

Conventional nozzles are a simple way to de-liver foam solution with existing equipment whenthe objective is rapid wetting of the fuel and foamis not needed. The unstable foam applied in thismanner is essentially wet water that enhanceswetting of fuel, penetration, and spread of thewater but does not give sufficient foam structureto provide insulation or heat reflection.

Aspirating NozzlesAspirating nozzles are low-energy systems con-sisting of standard water pumping apparatus tomove foam solution through the hose to a nozzle,which passes the foam solution through a ven-turi like device to add air, creating foam.

At the nozzle, foam solution is constricted andbroken into fine streams, creating a pressure dropon the back side of the venturi. Air is drawn intothe nozzle either through openings placed radi-ally in front of the expansion chamber or throughteeth placed at the end of the chamber. In theexpansion chamber, bubbles are formed, ex-panded, and combined to make foam. Thisprocess of pulling in air and spreading out in alarger diameter chamber costs energy. Dischargedistance is dependent on the size of the cham-ber and the direction and volume of air flow.

Bubble size is variable and the conversion effec-tiveness of water to foam can be as high as 65percent. Nozzles with larger expansion cham-bers create a drier foam with larger bubbles buttheir discharge distance is short, whereas a wet-ter foam made in a nozzle with a smaller expan-sion chamber can be propelled a greater distance

SPRAY

FOG

STRAIGHT-STREAM

SPRAY

FOG

FOAMSOLUTION WATER

PUMPASPIRATING

NOZZLE

(Foam forms in nozzle)

FOAMSOLUTION

DRAW IN AIR(Air drawn into

the front)

➤

➤

FOAMSOLUTION

AIR FOAM

➤

➤

➤

➤

➤

➤➤➤

➤➤➤➤➤

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HOSE STREAMRESTRICTION

ADDAIR

AIR & SOLUTION MIXING

NOZZLE

ATOMIZESOLUTIONSTREAM

➤

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15

foam type. Static pressures of air and watershould be nearly equal. Flow pressures drop offuntil the back pressure in the hoselay is too greatto overcome. A pressure gauge at the point ofmixing helps determine when this maximum hoselength has occurred.

A water flow meter is recommended because itindicates to the operator how wet or dry the foamis at the nozzle and provides a reference for anychanges to be made in the foam. The waterflow meter should be located before the checkvalves. Flow meters require specific lengths ofstraight bore flow for proper measurement.

Beyond the flow valves, the foam solution andair are mixed to produce bubbles. Most CAFSrely on the length of hose to provide the agita-tion and mixing necessary to produce foam. Asthe bubbles travel through the hose they clingto the hose linings and to other bubbles. Thisfriction further agitates the foam. If the hose islong enough, the foam is agitated to a point whereall the bubbles are tiny and uniform in size andwater content. These bubbles create a foamplug against which oncoming foam is compressedas it in turn forms into tiny, uniform bubbles. Thisprocess is called scrubbing. As the foam ap-proaches the end of the hose, it increases invelocity as the compressed air begins to expandto atmospheric pressure.

COMPRESSEDAIR

CHECK VALVE

FLOW VALVE

GATED WYE

PRESSUREGAUGE

PRESSUREGAUGE

WATERPUMP

MIN OF 150ft 1-1/2" HOSEMIN OF 100ft 1" HOSE

Pressure reading on waterside and air side needsto be the same at static.

FOAMSOLUTION

CHECKVALVE

1/4-TURNBALL

VALVE

hose friction or a mixing device. Because com-pressed air systems use brute force to producefoam, they can be used with almost any foamingagent to make foam.

As a general rule, the mix ratio for CAFS shouldstart at 0.3 percent. This is less than other sys-tems because the blending of air and foam so-lution is more efficient. The primary componentsof this system are the water pump and the aircompressor. Many combinations of pump andcompressor styles are possible. Centrifugal pumpsand rotary screw compressors best meet thedemands of the system. The use of the com-pressor should add to the performance of thewater pump. It should never reduce the full per-formance of the pump alone. The inputs of airand water should be matched at the ratio of 1gallon per minute of water for every cubic foot perminute of air.

Other essential components are flow valves andcheck valves for air and water. The flow valvescontrol inputs to the mixing chamber where airand foam solution meet. The check valves pre-vent water from flowing into the air compressorand air from flowing into the water pump.

Pressure gauges and adjustable valves for airand water are necessary to produce the desired

16

Bubbles are created by either the scrubbing ac-tion of the hose line or by a mixing chamber.The length of hose required for scrubbing de-pends upon the type and diameter of hose andthe mix ratio. For example, scrubbing of 0.3percent solution foam in 1-inch cotton jacketrubber-lined hose occurs within 50 feet at ap-proximately 65 °F; 0.3 percent foam in 1.5-inchwoven rubber hose requires 100 feet or more.

There are mixing devices that eliminate the needfor long lengths of hose. These use motionlessmixers which bring water, concentrate, and airtogether in a short space. Various designs existwhich produce foam with little or no loss in pres-sure. These motionless mixers are especiallyuseful for engine-mounted foam monitors and ap-plicators which have no need for long lengths ofhose.

Conventional and variable pattern nozzles, wands,and other attachments are compatible with aCAFS. The bigger the waterway the greater theflow. A one-quarter turn ball valve that has awaterway equal to the hose inside diameterprovides the greatest foam flow. Any restrictionof foam flow mechanically breaks down the bubblestructure creating a more fluid foam. A combi-nation barrel nozzle tip can be used to break upthe bubble structure of the foam and create ahigh-pressure foam solution for rapid penetra-tion. At pressures above 125 psi, horizontal pump-ing distance of foam and water are similar, whilevertical pumping loft is much higher with foam.

Continuous, unimpeded foam flow requires theuse of hose that is resistant to kinking. Wovenrubber hose is very kink resistant; extruded rubberhose and cotton jacket rubber-lined hose are fairlyresistant to kinking. Synthetic hose kinks easilywhen filled with foam.

Aerial DeliveryAir shear is the only mechanism for incorporat-ing air to generate the bubble structure whensolutions are delivered by airtankers, helitankers,and helibuckets. How efficiently the solution isconverted from a liquid to a foam depends onthe volume of solution making up the parcel ofliquid, the air speed, the drop height, and themix ratio. Exiting liquid is sheared only on theperiphery of the solution package; consequentlythe smaller the volume the more rapid is foamgeneration. The rate at which the outer bound-aries of the fluid mass are aerated depends onthe air velocity. Gravitational force alone is not

adequate to generate a stable foam structure;consequently helicopters must fly at 30 mph orgreater to obtain adequate aeration. A drop heightof 100 feet is adequate when the solution exitrate is slow but as the volume in the exiting massincreases, drop height must be increased up toas much as 500 feet above canopy to achievefoam formation. An increase in the mix ratioworks the same as increased aircraft speed orincreased drop height.

Equipment Maintenance and HousekeepingGuidelines for maintenance and housekeepingfollow.

• All foam concentrates have a detergent base.Therefore, cleansing of all plumbing, pumps,tanks, and other exposed surfaces can beexpected. This may promote the corrosiveactions of water.

PHOTO NOT AVAILABLE

PHOTO NOT AVAILABLE

17

• Flush pumps exposed to foam solution for20 minutes at the end of each shift.• Existing rust, scale, or dirt will be cleanedfrom inside your tank, and may plug the nozzle,pressure gauge parts, etc.• Proportioning devices which place foam con-centrate on the discharge side of the pumpare recommended to minimize corrosion prob-lems associated with foam.• Galvanized or fiberglass tanks for water andplastic or fiberglass tanks for foam concen-trate are preferred.• Recommended general housekeeping prac-tices include:

—Washing concentrate storage tank andengine body.

—Flushing injection systems and pumps.—Using pour spouts when transferring con-centrate.

APPLICATIONBasic ConsiderationsThis section provides an overview of foam char-acteristics that aid in fire suppression efforts andovercome problems that may be encountered.Remember that class A foam makes water workmore effectively in all fire applications. Water aloneworks on one side of the fire triangle; straightstreams are 5 to 10 percent effective at extin-guishment. Water that is applied as a foam workson all three sides of the fire triangle.

As a foam, water is most efficiently turned tosteam, absorbing heat. Foam itself has nochemical or long-term retardant effect. Foam’sperformance is determined by its drain rate, ex-pansion ratio, and surface tension. The inabilityto generate useful foam may be due to use ofthe wrong type of foaming agent, foam genera-tor problems, improper application, or inappro-priate expectations of the foam’s performance.

One important feature of foam is that the appli-cator can see where it has been applied; andfoam tends to stay where it is applied. In gen-eral, as long as foam is visible, the treated fuelremains wet. However, a foam’s effectivenessas a barrier should not be judged by visibilityalone. Fire may burn under or through a thickblanket of foam that drains too slowly to wetadjacent fuels, while a rapidly draining foam thatdisappears quickly may leave behind very wetfuels as the draining fluid penetrates the fuels.The amount of water absorbed depends on theamount of water (as foam) applied, the amountof water evaporated, the foam stability, and thefuel type.

The techniques employed with a CAFS and as-pirated nozzles are basically the same as whenusing a water stream. However, with foam, lesstime will be necessary in any given location orsituation than with water.

Water flow must fit the task. Recognize thatsome foam generating devices may flow morewater than conventional systems. Operators mustlearn to let foam work for them, allowing theoperator to complete the task more efficiently.

Foam should quickly penetrate live and dead fuels,charred fuels, and litter and duff material andimmediately knock down and extinguish flamesand eliminate smoke when applied at the baseof the flames. Foam can also be made to forma short-term foam layer that is greater than 1/2 inch on trees, snags, roofs, walls, eaves, andvehicles.

Width and depth of application depend primarilyupon wind, temperature, fuel moisture, and fuelloading and change as any of these factorschange. Foam should be applied to provideenough water and the appropriate rate of drain-age necessary to accomplish the task. The depthof the foam blanket and the amount of wateravailable for wetting must increase as the fireintensity increases.

Foam durability depends on the weather. Foamwill be visible in exposed areas for about 1 hourin hot weather, for up to 4 hours in cool weather,and in shaded areas will be visible even longer.CAFS foam will generally last longer than aspi-rated nozzle foam because of its stronger, moreuniform bubble structure.

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FUEL

18

Apply foam directly to the fuel from a short dis-tance at high pressure for maximum penetrationof foam mass into ground and surface fuels. Thenapply the foam from a distance and with a tra-jectory to allow the flakes of bubbles to settlegently upon the fuel. This technique, known aslofting, provides greater coverage of fuel surfacesand reduces bubble breakdown on impact. Aninsulating, reflecting water barrier is formed.

On fireline applications most work can be ac-complished from the fireline; but fuels should betreated from two angles to ensure coverage. Foamline width depends on the fuel and expected firebehavior conditions. To ensure thorough coat-ing, apply foam to all exposed sides of the fueland, when possible, to ladder and crown fuelsabove the foamline. A high-pressure streamdirectedinto the fuels at the interface of fireline andfoamline ensures wetting through the entire depthof fuel and minimizes the likelihood ofunderburning.

To provide adequate water for wetting below theinsulative foam blanket, foam solution can alsobe used. Apply foam solution to wet the areaentirely. Because foam agents wet living, dead,charred, and uncharred fuels, they are recom-mended for this treatment over standard wettingagents which wet charred fuels only.

Foam applied to protect seed trees, wildlifetrees,snags, log decks, telephone poles, and otherresources and properties should be a fluid or dryfoam that will cling to vertical, upside-down, slip-pery surfaces in sufficient quantities to form aprotective blanket. More time may be requiredthan for fireline application to adequately protectthese types of fuels. Surrounding fuels shouldbe treated from 25 to 50 feet out from the baseof standing objects. Time of application beforeignition is the same as with other foamline ap-plications.

The abilities of foam to penetrate dead andlive fuels quickly, to form an insulating blan-ket, to cling to vertical surfaces, and to reachgreat distances from the nozzle have pro-vided a powerful new tool for fuel protection.Foam can prevent fire spread. It can protectstands of timber, structures, wildlife habitat,fuelwood concentrations, endangered plants,and other resource values. Foam accom-plishes extinguishment with less applicationtime, with fewer personnel, and less waterthan conventional water applicaton.

FOAM TYPE CHARACTERISTIC

Solution A clear to milky fluid, lacksbubble structure, mostly water

Wet Watery, large to small bubbles,lacks body, fast drain times

Fluid Similar to watery shaving cream,medium to small bubbles,flows easily, moderate drain times

Dry Similar to shaving cream,medium to small bubbles, mostlyair, clings to vertical surfaces,slow drain times

Prescribed FireThe foam characteristics most important to fuelprotection are wetting ability and durability. Thefoam must break down sufficiently to wet the fuels,but must remain stable to maintain a protectivebarrier.

The amount of foam required for fuel protectiondepends on air temperature, wind, relative hu-midity, fuel loading, and the fuel’s moisturecontent. Foam is a very short-term treatment ona hot, dry, windy day. It is most effective whenapplied prior to ignition, allowing only enoughtime for the treated fuels to be wetted by mois-ture escaping from the foam blanket.

In general, the more adverse the burning con-ditions, the shorter the time between foam ap-plication and ignition should be. The need torepeat the treatment should also be consideredwhen ignition time must be delayed. Start witha 0.3 percent foam solution for CAFS or 0.5percent for aspirating nozzle systems and adjustthe mix ratio to obtain the required foam type.

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19

SUPPRESSIONInitial Attack

DirectThe ability of foam to continue wetting and coolingfuels long after the application is completed isa key to foam use strategies. Greatest efficiencyis achieved with continuous, rapid application;knocking out the flaming fire front, blanketingsmoldering stumps, and allowing the foam to workwhere it is applied.

A good starting point is a 0.3 percent mix ratiofor CAFS, and 0.5 percent for aspirating nozzlesystems. Make adjustments to the mix ratio toproduce foam solution, wet foam, or fluid foamto meet the needs of the particular situation. Hardor saline water may require a higher mix ratiothan with other water to produce comparable foam.

Application of foam to the base of a linear flamefront is crucial to minimize losses due to heatand updraft. Hotspots should be secured firstaround the edge, and then the interior should beblanketed. While attacking the edge, a portionof the foam stream should be directed onto theadjacent unburned fuels. The stream initially maybe directed at very hot or distant flames to allowsafer approach to the fire front.

When penetration into burning material is nec-essary, increase the application or impact froma short distance; apply enough to ensure extin-guishment. Since foam is highly visible, over-application can be minimized. Work quickly—assoon as steam is visible move on. Leave a foamblanket over the hot fuel to smother it, and con-tinue to wet and cool the fuel. Proceed to coatadditional untreated fuels.

OPERATING GUIDELINESFoam Delivery SystemsAny of the foam proportioning/mixing methods canbe used with any foam generating device. Auto-matic regulating devices are preferred for com-pressed air foam systems to prevent slug flow.

Conventional Nozzles1. 0.1 to 0.3 percent mix ratio2. Match gpm flow to task.

Aspirating Nozzles1. 0.2 to 1.0 percent mix ratio, dependent

on nozzle and type of application, with ad-justments to best meet the needs and objec-tives as dictated by fuels and fire behavior.

2. Match gpm flow to task.

CAFSCAFS can operate at any water flow the

pump and hose can handle. Water flow canbe adjusted at the engine or the nozzle. At150 psi and maximum air:

Hose Maximum Maximum(in) Water Flow Discharge

1.0-inch hose 20 gpm 80 ft1.5-inch hose 40 gpm 100 ft2.5-inch hose 80 gpm 180 ft

Compressed air foam can be adjusted by chang-ing any of the three inputs—air, water, concen-trate.

1. Keep static air and water pressures equal.2. Start with a 0.3 percent mix ratio.3. Maximum production/output.

• 30 gpm/30 cfm for one 1-inch hose• 60 gpm/60 cfm for one 1.5-inch hose

or two 1-inch hoses.• 100 gpm/100 cfm for one 2.5-inch hose;two 1.5-inch hoses; five 1-inch hoses.

4. Operate with 1 cfm of air for every gpmof water.5. 100 feet of hose or a motionless mixer6. Match gpm flow to task.

Aerial Generating SystemsMix ratios of 0.5 to 0.6 percent are commonlyused.

20

Engine-mounted monitors maybe used for pump and roll-typeoperations. An added benefit offoam is that it can be used toput out fires whose extinguish-ment would not be possiblewith plain water—such as firesinside and at the top of snagsand fire in log decks. As water

drains out and off, foam fillsthe voids and clings to

surfaces. Torching andcrowning fires in tree

tops can be extin-guished if the

crowns arew i t h i n

reach ofthe foamstream.

IndirectMix ratios of 0.3 percent for CAFS and 0.3 to 0.5percent for aspirating nozzle systems are appro-priate starting points. Apply foam as a wet lineat least two and a half times as wide as theexpected flame lengths adjacent to a back fire.Apply foam directly at close range and attemptto coat all sides of fuel to the ground. Foam canalso be lofted onto brush, tree trunks, and cano-pies to add an insulating barrier. Allow time forwetting of fuels where possible.

Water in the foam is doing the work against thefire. The effectiveness of a foam line in indirectattack is limited by the time it takes the waterto evaporate.

Structure ProtectionThe ability of foam to adhere to vertical, sloped,undersides, and slippery surfaces is the key tostructure protection. Start with a 0.3 percentmix ratio for CAFS or a 0.5 percent for aspirat-ing nozzles and adjust the mix ratio as neces-sary to obtain the desired foam consistency. Applya dry foam to outside walls, eaves, roofs, col-umns, or other threatened surfaces, lofting it ratherthan directing it at the surfaces to avoid foambreakdown and runoff due to impact of additionalfoam. Durability is dependent on weather andfire behavior conditions. In general, CAFS foamshould last for 1 hour in hot weather, nozzleaspirated foam for about 30 minutes. The ef-fectiveness and life of the foam blanket is de-pendent on foam dryness and the depth of ap-plication. At least 1/2 inch of foam should re-main on all surfaces, even if excess amountsslough off.

Depending on the fire intensity, foam can be usedsuccessfully to prevent wildland and structure firesfrom igniting adjacent structures. However, if astructure becomes involved, foam-treated wallsalone may not save it because the water require-ment for preventing combustion may be greaterthan the water applied as foam.

Mop-upFoam’s extinguishing, penetrating, and discharge dis-tance capabilities allow mop-up operations to begin earlierand take less time to complete. The smothering actionof the foam and the penetration of the solution can beused soon after flames subside to extinguish fire before

it burns underground, eliminat-ing residual smoke, reduc-

ing reburn potential,and minimizing

soil erosion.

Hand tools, mop-up wands, and forester nozzlescan be used with compressed air foam or foam

To knock fire out ofsnags or trees

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Backpack PumpsBackpack pumps with conventional fog andstraight-stream tips can be used to deliver foamsolution. A mix ratio of 0.05 to 0.1 percent iscommon for this type of application. To avoidexcessive foaming, the foam concentrate shouldalways be added to water once the container isfilled. Because the detergent properties of thefoam solution strips the lubricant from the pumpwand periodic lubrication of the pump is required.

Application techniques are the same for foamsolution as for water, except that the quantityneeded for a given task is less. Aspirating nozzlesare available for use with a backpack pump, butaeration is incomplete. The wet foam or foamsolution produced is suitable for hand suppres-sion and mop-up activities.

SUMMARYFoams:

1. Enable water to most efficiently absorb heat by forming water into a thin film.2. Protect fuels from ignition by:

a. Suppressing vapors.b. Wetting fuelsc. Insulating fuels from flame, heat, and

oxygen.d. Reflecting heat from fuels.

3. Are more effective because:a. They can hold water in place over time.b. They spread water to a thin film en

abling increased penetration and spreading.

4. Reduce smoke and related emissions.5. Raise humidity of treated air space.

solution for mop-up operations. Application tech-niques are the same as those for plain water,but the water, aided by the wetting agents con-tained in the foam, does the work more efficiently.

Start with a 0.2 percent solution for CAFS or 0.3for nozzle aspirating systems. Application of thefoam should begin on the burn edge and workshould progress inward with particular attentionto hot spots. Any remaining flames should beattacked directly.

By partially closing the valve, when a CAFS isused, to strip air from the foam it is possible to

create a high-pressure wet water mistfor close-in general coverage, af-

ter which attention can be con-centrated on hot spots. A com-

bination barrel nozzle tip canalso be used to strip the

air from the foam whena wet water applica-

tion is required.

For surface fires, a wet foam can penetrate thefuel quickly to cool and smother the fire and createan oxygen barrier around any remaining smolder-ing fuel. This strategy works extremely well onpitchy and punky material, duff and litter material.

Avoid applying dry foam during mop-up. Thisslow-draining foam forms a lid over deep-seatedfires, trapping heat. Pockets of low-level com-bustion may show up as steam plumes or aspatches with no foam remaining. These placesshould be treated again.

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CLASSIFICATION SYSTEM FOR APPLICATION OFWILDLAND FIREFIGHTING FOAMS

TYPICAL USES• Direct attack on fine fuels or desert typefuels• Mop-up• Deep duff and anywhere fuel penetrationis essential• Tall grass and deep fine fuels• Muskeg, tundra, sawdust pits and piles,peat, and other such deep-seated fires• Aerial application, canopy penetration

EQUIPMENT REQUIRED TO PRODUCE• Proportioner• Low-expansion aspirated nozzles• CAFS units• Aircraft

“Fluid” Foam

CHARACTERISTICSThe bubbles of “FLUID” foams are mostly spheri-cal. There is less separation of bubbles by thesolution than with wet foam. Some of the bubblewalls may be touching. Fluid foams have me-dium to fast drainage rates.

DESCRIPTION• Watery shaving cream• Does not hold peaks• Flows readily from vertical surfaces• Medium to small bubbles• Flows easily• Moderate drain rates

TYPICAL USES• Direct attack on most fuels• Protection of vertical surfaces• Protection of standing timber• Protection of structures• Prescribed burn fuel protection• Mop-up• Aerial penetration of forest fuels• Fuel or resource protection for shortperiods (less than 30 minutes)• Grass and fine fuels

EQUIPMENT REQUIRED TO PRODUCE• Proportioner• Low-expansion aspirating nozzles• CAFS units• Aircraft

6. Fills vertical cavities; not affected by grav-ity.

Several types of foams can be created with thefoam generating equipment discussed. Each ofthem has a role in the wildland fire suppression.Listed below are the foam types and associatedcharacteristics.

Foam “Solution”

CHARACTERISTICSFoam “SOLUTION” has no real bubble structurebut some bubble formation may occur due toagitation and impact.

DESCRIPTION• A clear to milky fluid• No bubble structure• Mostly water• Immediately runs off vertical surfaces

TYPICAL USES• Areas requiring immediate penetration• Thick fuel beds like sawdust piles, peat, tundra, and muskeg• Tall grass• Deep-seated fires• Mop-up

EQUIPMENT REQUIRED TO PRODUCE• Proportioner• Conventional nozzles• CAFS (using conventional nozzles or partially opened shut-off valve)

“Wet” Foam

CHARACTERISTICSThe bubbles of “WET” foams are spherical massesof air which are enclosed in solution. The bubblewalls are separated by a large amount of solu-tion, relative to other types of foams. Wet foamshave very fast drainage rates.

DESCRIPTION• Watery• Very runny on vertical surfaces• Bubble size varies from large to small• More water than air• No ‘body’• Fast draining

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“Dry” Foam

CHARACTERISTICSThe bubbles of “DRY” foams are polyhedral inshape. The bubble walls are very thin with onlysmall amounts of solution between the bubbles.These types of foams have very slow drainagerates.

DESCRIPTION• Shaving or whipped cream• Medium to small bubbles• Mostly air• Very “dry” and fluffy• Clings to vertical surfaces• Holds peaks for a long time• Slow drain times

TYPICAL USES• Insulating ground and ladder fuels• Visible barriers for long time periods (greaterthan 30 minutes)• Protection of structures and other verticalsurfaces• Protection of standing timber

EQUIPMENT REQUIRED TO PRODUCE• Proportioner• CAFS units• Low-expansion aspirating nozzles

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GLOSSARY OF TERMS

AbsorptionThe act of absorbing or being absorbed.

AdherenceSee viscosity.

Agent ConcentrateThe fire chemical product as received from thesupplier that, when diluted with water, becomesfoam solution.

Agent SolutionThe dilute working-form of foam concentrate towhich air is added to produce foam.

AspirateTo draw in air; nozzle aspirating systems draw airinto the nozzle to mix with the agent solution.

AutomaticReadily adjusts to changes in water flow and orpressure to maintain a desired mix ratio.

BalancedSee Automatic.

BarrierAny obstruction to the spread of fire; typically, anarea or strip devoid of flammable fuel.

Batch MixManual addition of foam concentrate to a waterstorage container or tank to make foam solution.

BiodegradationDecomposition by microbial action, as with somedetergents.

BlanketA body of foam - used for fuel protection and/orsuppression.

BubbleThe building block of foam; bubble characteristicsof water’s content and durability influence foamperformance.

CarcinogenicCancer-causing.

Class A FireFire in “ordinary” combustible solids. (However,if a plastic readily melts in a fire, it might be ClassB rather than Class A.)

Class B FireFire in flammable liquids, gasses, and greases.

Class A FoamFoam intended for use on Class A or woody fuels;made from hydrocarbon-based surfactant, there-fore lacking the strong filming properties of Class Bfoam, but possessing excellent wetting properties.

Class B FoamFoam designed for use on Class B or flammableliquid fires; made from fluorocarbon-based surfac-tants, therefore capable of strong filming action,but incapable of efficient wetting of Class A foam.

Combination NozzleAlso called an “adjustable fog nozzle.” This nozzleis designed to provide either a solid stream or afixed spray pattern suitable for water or wet waterapplication.

Compressed Air Foam Systems (CAFS)A generic term used to describe foam systemsconsisting of an air compressor (or air source),a water pump, and foam solution.

ConcentrateA substance that has been concentrated; specifi-cally, a liquid that has been made denser, as bythe removal of some of its water.

ConsistencyUniformity and size of bubbles.

CorrosionResult of chemical reaction between a metal andits environment (i.e., air, water, and impurities insame).

DegradationThe act of degrading or being degraded in rank,status, or condition.

DensityThe amount of foam solution in the foam (notedifference from “expansion”).

Drain TimeThe time (minutes) it takes for foam solution todrop out from the foam mass for a specified percentof the total solution contained in the foam to revertto liquid and drain out of the bubble structure.

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Foam SystemsThe apparatus and techniques used to mix con-centrate with water to make solution, pump andmix air and solution to make foam, and transportand eject foam. (Systems defined here includecompressed air foam and nozzle aspirated.)

Foam TypeA combined measure of drain time and expansionto describe durability, consistency, viscosity, anddensity.

InductorA control mechanism that allows a regulated quantityof foam concentrate to be introduced into the mainhose line.

IngestionTo take things into the body (food, drugs, etc.) byswallowing or absorption.

IngredientEach chemical component used in the formulationof a product.

ManualWorked or done by hand and not by machine.

Manual RegulationA proportioning method or device that requires amanual adjustment to maintain a desired mix ratioover a changing range of water flows and pres-sures.

Mix RatioThe ratio of liquid foam concentrate to water, usuallyexpressed as a percent.

Mixed SolutionThe combination of water and foam concentrateused to produce the foam used for fire suppression.

Mixing ChamberA tube drilled, with deflectors or baffles, that producestiny, uniform bubbles in a short distance (1 to 2ft).

MonitorA turret-type nozzle usually mounted on an engine.

MutagenicAny agent or substance capable of noticeablyincreasing the frequency of mutation.

DurabilityThe effective life span of foam bubbles.

EductorA mixing system that uses water pressure to drawthe fire chemical into the water stream for mixing;enables a pump to draw foam concentrate, as wellas water, into the hose line.

EjectorOccasionally an injector is used to proportion mixes;this type of equipment is frequently referred to asan “ejector,” though sometimes as an “injector.”

EnvironmentSomething that surrounds; surroundings, such asair, water, or natural resources.

ExpansionThe ratio of the volume of the foam in its aeratedstate to the original volume of the non-aerated foamsolution.

Fire RetardantAny substance that by chemical or physical actionreduces the flammability of combustibles.

FoamThe aerated solution created by forcing air into,or entraining air in, a water solution containing afoam concentrate by means of suitably designedequipment or by cascading it through the air ata high velocity.

Foam ConcentrateThe concentrated foaming agent as received fromthe manufacturer; use only those approved for usein wildland fire situations by the authority havingjurisdiction.

Foam GenerationThe foam production process of solution agitationin a hose, mix chamber, or nozzle.

Foam LineA body of foam placed along areas to be protectedfrom fire; also used as an anchor for indirect attackin place of hand-made fire trail.

Foam SolutionA homogeneous mixture of water and foam con-centrate in a proportion that meets the needs ofthe user.

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Nozzle Aspirated Foam SystemA foam generating device that mixes air at atmo-spheric pressure with foam solution in a nozzlechamber.

ProportionerPumps foam concentrate, as demanded into thehose line.

ReproductiveThe process, sexual or asexual, by which animalsand plants produce new individuals.

ScrubbingThe process of agitating foam solution and airwithin a confined space (usually a hose) that producestiny, uniform bubbles - the length and type of hosedetermine the amount of scrubbing and, therefore,foam quality.

Short-Term RetardantA viscous, water-based substance wherein wateris the fire suppressing agent.Slug Flow: In CAFS only, when foam solutionis not rich enough to mix with air, inadequatemixing occurs; this sends pockets (or plugs) ofwater and air to the nozzle.

StabilitySee Viscosity.

SuppressantAn agent used to extinguish the flaming and flowingphases of combustion by direct application to theburning fuel.

Surface TensionThe elastic-like force in the surface of a liquid,tending to minimize the surface area and causingdrops to form. (Expressed as Newtons per meteror dynes per centimeter; there are 1,000,000 dynesper Newton.)

SurfactantA surface active agent; any wetting agent.

Use LevelThe appropriate ratio of liquid foam concentrateto water recommended by the chemical manufac-turer for each class of fire.

VariableSee Automatic.

ViscosityAn indication in the ability of the foam to spreadand cling, as well as to cling to itself, upon delivery.

Wet WaterWater with added chemicals, called wetting agents,that increase water’s spreading and penetratingproperties due to a reduction in surface tension.

Wetting AgentA chemical that, when added to water, reducesthe surface tension of the solution and causes itto spread and penetrate exposed objects moreeffectively.

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SOURCES OF INFORMATION

Cote, Arthur E. 1986. Fire Protection Handbook,16th edition. National Fire Protection Associa-tion, Quincy, Massachusetts.

Friedman, Raymond 1989. Principles of FireProtection Chemistry, 2nd edition. National FireProtection Association, Quincy, Massachusetts.

International Fire Service Training Association1983. Essentials of Fire Fighting, 2nd edition.Fire Protection Publications, Stillwater, Oklahoma.

Liebson, John. Introduction to Class A Foamsand Compressed Air Foam Systems for the Struc-tural Fire Service. Copies available from theInternational Society of Fire Service Instructors,Ashland, Massachusetts, ISBN 0-929662-08-3

McKenzie, Dan W. Proportioners For Use inWildland Fire Applications, 9251 1204—SDTDC.Copies available from Technology & DevelopmentCenter, USDA Forest Service, 444 E. Bonita Ave.,San Dimas, California.

McKenzie, Dan W. Compressed Air Foam Sys-tems for Use in Wildland Fire Applications, 92511203—SDTDC. Copies available from Technol-ogy & Development Center, USDA Forest Ser-vice, 444 E. Bonita Ave., San Dimas, California.

Moore, James E., Johansen, Ragnar W., Mobley,Hugh E. Jr. 1976. Southern Guide For UsingFire Retarding Chemicals in Ground Tankers.Atlanta, GA: U.S. Department of Agriculture, ForestService, State & Private Forestry, SoutheasternArea. 9 p.

NFPA, 298, 1989. Foam Chemicals for WildlandFire Control. National Fire Protection Associa-tion, Quincy, Massachusetts.

Norecol Environmental Consultants Ltd. 1989.Toxicological Review of Fire Fighting Foams.Prepared for Manager, Fire Management ForestProtection Branch, Ministry of Forests and Lands,Victoria, BC, Canada.

NWCG Fire Equipment Working Team, Foam TaskGroup. Foam Applications for Wildland & UrbanFire Management. Copies available from Tech-nology and Development Center, USDA ForestService, 444 E. Bonita Ave., San Dimas, Cali-fornia.

NWCG Fire Equipment Working Team, Foam TaskGroup. Foam vs Fire—Primer. Copies availablefrom the National Interagency Fire Center, 3905Vista Ave., Boise, Idaho, 83705. NFES 2270

NWCG Fire Equipment Working Team, Foam TaskGroup. Foam vs Fire—Class A Foam for Wild-land Fires. Copies available from the NationalInteragency Fire Center, 3905 Vista Ave., Boise,Idaho 83705. NFES 2246

NWCG, NWST, 1992. Foambib, A Bibliographyof Wildland Fire Foam Evaluation and Use.National Wildfire Suppression Technology Group.Intermountain Fire Sciences Laboratory, P.O. Box8089, Missoula, Montana 59807

Parminter, John 1989. A Primer On WildlandFire-Fighting Foams. Ministry Of Forests, BritishColumbia, Canada.

Seevers, Melinda R. and John A., Field Surveyof Helicopter Foam Injection Systems. Copiesavailable from Technology & Development Cen-ter, USDA Forest Service, 444 E. Bonita Ave.,San Dimas, California 91773.

USDI-BLM. A Performance Test of Low Expan-sion Nozzle Aspirated Systems and Class A Foam,2nd Edition. National Interagency Fire Center,3905 Vista Ave., Boise, Idaho 83705

The National Wildfire Coordinating Group (NWCG)has sponsored the publication of the followingvideos produced by the NWCG Fire EquipmentWorking team. Copies of each of these itemsmay be ordered from the National InteragencyFire Center (NIFC). Attn: Supply, 3905 VistaAvenue, Boise, Idaho 83705

Introduction to Class A Foam, 1989NFES #2073

The Properties of Foam, 1992,NFES #2219.

Class A Foam Proportioners, 1992,NFES #2245

Aspirating Nozzles, 1992,NFES #2272

Compressed Air Foam Systems, 1993,NFES #2161

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THE METRIC SYSTEM AND EQUIVALENTS

The purpose for including the following metric system equivalents and approximate conversion factors isto meet the requirements of Public Law 100-418. This law requires each Federal agency to use the metricsystem of measurement by Fiscal Year 1992, in procurements, grants, and other business related activities.

Linear Measure Liquid Measure

1 centimeter= 10 millimeters= 0.39 inch 1 centiliter= 10 milliliters= 0.34 fl ounce

1 decimeters= 10 centimeters= 3.94 inches 1 deciliter= 10 centiliters= 3.38 fl ounces

1 meter= 10 decimeters= 39.37 inches 1 liter= 10 deciliters= 38.82 fl ounces

1 dekameter= meters= 32.80 feet 1 dekaliter= 10 liters= 2.64 gallons

1 hectometer= 10 dekameters= 328.08 feet 1 hectoliter= 10 dekaliters= 26.42 gallons

1 kilometer= 10 hectometers= 3,280.8 feet 1 kiloliter= 10 hectoliters= 264.18 gallons

Weights Square Measure

1 centigram= 10 milligrams= 0.15 grain 1 sq centimeter= 100 sq millimeters= 0.155 sq in

1 decigram= 10 centigrams= 1.54 grains 1 sq decimeter= 100 sq centimeters= 15.5 sq in

1 gram= 10 decigrams= 0.035 ounce 1 sq meter (centare)= 100 sq decimeters= 10.76 sq ft

1 dekagram= 10 grams= 0.35 ounce 1 sq dekameter (are)= 100 sq meters= 1,076.4 sq ft

1 hectogram= 10 dekagrams= 3.52 ounces 1 sq hectometer (hectare)=100 sq dekameters= 2.47 acres

1 kilogram= 10 hectograms= 2.20 pounds 1 sq kilometer= 100 sq hectometers=0.386 sq mi

1 quintal= 100 kilograms=220.46 pounds

1 metric ton= 10 quintals= 1.1 short tons

Cubic Measure

1 cu centimeter= 1000 cu millimeters= 0.06 cu inch

1 cu meter= 1000 cu decimeters= 35.31 cu feet

1 cu decimeter= 1000 cu centimeters= 61.02 cu inches

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APPROXIMATE CONVERSION FACTORS

To Change To Multiply By To Change To Multiply By

inches centimeters 2.54 ounce-inches newton-meters 0.007062

feet meters 0.305 centimeters inches 0.394

yards meters 0.914 meters feet 3.280

miles kilometers 1.609 meters yards 1.094

square inches square centimeters 6.451 kilometers miles 0.621

square feet square meters 0.093 square centimeters square inches 0.155

square yards square meters 0.836 square meters square feet 10.764

square miles square kilometers 2.590 square meters square yards 1.196

acres square hectometers 0.405 square kilometers square miles 0.386

cubic feet cubic meters 0.028 square hectometer acres 2.471

cubic yards cubic meters 0.765

cubic meters cubic feet 35.315

fluid ounces milliliters 29,573 cubic meters cubic yards 1.308

pints liters 0.473 milliliters fluid ounces 0.034

quarts liters 0.946 liters pints 0.2113

gallons (US) liters 3.785 liters quarts 1.057

liters gallons (US) 0.264

gallons (Imp) liters 4.546 liters gallons 0.264

liters gallons (Imp) 2.220 grams ounces 0.035

gallon (US) gallon (Imp) 0.333 kilograms pounds 2.205

gallon (Imp) gallon (US) 1.201 metric tons short tons 1.102

ounces grams 28.349

pounds kilograms 0.454 PSI kilopascals 6.895

short tons metric tons 0.907 kilopascals PSI 0.145

pound-feet newton-meters 1.365 acres hectares 0.405

pound-inches newton-meters 0.11375 hectares acres 2.470

Temperature (Exact)

°F=Fahrenheit °C=Celsius

°F=(°Cx9/5)+32 °C=5/9x(°F-32)