Fire Streams Module II & III. Fire Hydraulics Deal with properties of energy, pressure, and water...

Fire Streams

Module II & III

Fire Hydraulics

• Deal with properties of energy, pressure, and water flow as related to fire suppression.

Flow

• Volume of water that is being moved • Measured in gallons per minute (gpm) • Metric measured in liters per minute (lpm)

Pressure

• Amount of energy in a body or stream of water

• Measured in pounds per square inch (psi) • Metric measured in kilopascals (kPa) • Required to push water through a hose or

to a higher level • Pumps usually provide the pressure.

Friction Loss

• Loss of pressure as water moves through a pipe or hose

• Loss represents the energy required to push the water. – Greater flow in same hose, greater friction

loss – Smaller hose with same flow, greater friction

loss – All else equal, loss proportional to distance

Elevation Pressure

• Elevation affects water pressure. • Elevated water tanks supply pressure to

pipes due to elevation. • Difference between nozzle elevation and

engine elevation affects pressure.– Hoses laid downhill have greater pressure. – Hoses laid up stairs will have less pressure.

Water Hammer

• Surge in pressure caused by sudden stop in the flow of water

• Shock wave is transmitted back through the hose.

• Can damage hose, couplings, and plumbing

• To prevent, open and close valves slowly.

Foam

• Used to fight several types of fires • Used to prevent ignition of materials • Used to neutralize hazardous materials • Produced by mixing foam concentrate with

water and air

Foam Classifications (1 of 2)

• Class A foam – Used to fight fires involving ordinary

combustible materials – Increases effectiveness of water by reducing

the surface tension of water – Can be added to water streams and applied

with several types of nozzles

Foam Classifications (2 of 2)

• Class B foam – Used for class B fires – Specific foam varies by type of flammable

liquid – Separates fuel from the fire – Foam blanket must not be disturbed – Can be applied to flammable liquid spills to

prevent fire

Class A Foam Concentrates

• From 0.1% to 1% solution • “Wet” foam has good penetration

properties. • “Stiff” foam is more effective when applied

for protecting buildings.

Class B Foam Concentrates (1 of 3)

• Used as either 3% or 6% solution • Types of foams should not be mixed. • Brands of the same foams should not be

mixed. • Incompatible mixtures may congeal and

plug foam systems. • Older foams have environmental hazards.


• Protein foams – Made from animal byproducts – Effective on hydrocarbon fires

• Fluoroprotein foams – Made with same base materials as protein foam – Includes a flurochemical surfactant – Produce fast-spreading membrane – Provide a greater seal against edges of objects


• Aqueous film-forming foam (AFFF) – Synthetic base – Particularly suited for gasoline – Seals across surface quickly – Excellent vapor suppression ability

• Alcohol-resistant foam – Properties similar to AFFF – Won’t dissolve in alcohols and other polar

solvents

Ways Fire Fighting Foam Extinguishes/Prevents Fire

• Separating• Cooling• Smothering• Penetrating

Terms Associated With Foam

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

How Foam is Generated

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

(Continued)


• Elements needed to produce fire fighting foam

(Continued)

– Foam concentrate– Water

– Air– Mechanical agitation


• All elements must be present and blended in correct ratios

• Aeration produces foam bubbles to form effective foam blanket

Foam Expansion

• The increase in volume of foam when aerated

• Method of aerating results in varying degrees of expansion

• Types of foam

Foam Concentrates — General Considerations

• Foam concentrates must match fuel to which applied

• Class A foams not designed to extinguish Class B fires

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

Class A Foam

• Increasingly used in both wildland and structural fire fighting

(Continued)

Class A Foam

• Special formulation of hydrocarbon surfactants

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

• May be used with variety of nozzles

Class B Foam

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

(Continued)

Courtesy of Williams Fire & Hazard Control, Inc.

Class B Foam

• Used to suppress vapors from unignited spills of these liquids

• Several types of Class B foam concentrates available

(Continued)

Class B Foam

• Manufactured from synthetic or protein base

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

(Continued)

Class B Foam

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

(Continued)

Courtesy of Harvey Eisner.

Class B Foam

• Rate of application depends on several factors

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

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

Specific Application Foams

• Numerous types of foam available for specific applications

• Properties of foams vary

Proportioning

• Mixing of water with foam concentrate to form foam solution

• Most concentrates can be mixed with fresh/salt water

(Continued)

Proportioning

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

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

(Continued)

Proportioning

Proportioning Methods

• Induction

• Injection(Continued)

Proportioning Methods

• Batch-mixing

• Premixing

Courtesy of Ansul.

Foam Proportioners — General Considerations

• May be portable or apparatus-mounted• Operate by one of two basic principles

Courtesy of Conoco/Phillips.

Portable Foam Proportioners

• Simplest, most common form of proportioning devices

• In-line foam eductors• Foam nozzle eductors

Apparatus-Mounted Proportioners

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

• Three types

Compressed-Air Foam Systems (CAFS)

• Newer structural engines are equipped with CAFS

(Continued)


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

(Continued)


• Unlike other systems, hoseline contains finished foam

• Advantages• Disadvantages

Handline Nozzles

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

Medium- and High-Expansion Foam Generating Devices

• Produce foam that is semistable with high air content

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

Reasons for Poor-Quality Foam/Failure to Generate Foam

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

• Air leaks at fittings cause loss of suction

(Continued)


• Improper cleaning of proportioning equipment causes clogged foam passages

• Nozzle not fully open, restricting water flow

(Continued)


• Hose lay on discharge side of eductor is too long

• Hose is kinked and stops flow • Nozzle is too far above eductor

(Continued)


• Mixing different types of foam concentrate in same tank results in mixture too viscous to pass through eductor

Roll-On Foam Application Method

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

• Foam rolls across surface of fuel (Continued)

Roll-On Foam Application Method

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

• Used only on pool of liquid fuel on open ground

Bank-Down Foam Application Method

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

• Object may be wall, tank shell, similar vertical structure

(Continued)

Bank-Down Foam Application Method

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

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

Rain-Down Foam Application Method

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

(Continued)

Rain-Down Foam Application Method

• Primary manual application technique on aboveground storage tank fires

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

Foam Hazards to Humans

• Foam concentrates pose minimal health risks to humans

• May be mildly irritating to skin, eyes

(Continued)

Foam Hazards to Humans

• Affected areas should be flushed with water

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

• Consult MSDS for specific information

Foam Hazards to Equipment

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

• Follow proper flushing procedures to prevent damage

Foam Hazards to Environment

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

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

(Continued)


• Environmental impact of foam concentrates varies

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

(Continued)


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

• Protein-based foams safer for environment

(Continued)

Summary

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

Fire Streams Module II & III. Fire Hydraulics Deal with properties of energy, pressure, and water...

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