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.
Class B Foam Concentrates (2 of 3)
• 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
Class B Foam Concentrates (3 of 3)
• 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)
How Foam is Generated• Elements needed to produce fire fighting foam
(Continued)
– Foam concentrate– Water
– Air– Mechanical agitation
How Foam is Generated
• 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)
Compressed-Air Foam Systems (CAFS)
• 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)
Compressed-Air Foam Systems (CAFS)
• 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)
Reasons for Poor-Quality Foam/Failure to Generate Foam
• Improper cleaning of proportioning equipment causes clogged foam passages
• Nozzle not fully open, restricting water flow
(Continued)
Reasons for Poor-Quality Foam/Failure to Generate Foam
• Hose lay on discharge side of eductor is too long
• Hose is kinked and stops flow • Nozzle is too far above eductor
(Continued)
Reasons for Poor-Quality Foam/Failure to Generate Foam
• 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)
Foam Hazards to Environment
• Environmental impact of foam concentrates varies
• In the U.S., Class A foams should be approved by USDA Forest Service
(Continued)
Foam Hazards to Environment
• 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