09 Foam Flashcards
Foam
Was developed during the twentieth century as a way to fight flammable liquid fires.
Foam is made to
float on top of flammable liquids - preventing vapors from burning.
Finished foam is a combination of
- Foam Concentrate
- Water
- Air
(Mechanical Agitation “rounds” out the Foam Tetrahedron)
Foam extinguishes flammable or combustible liquid fires in four ways:
- Excludes air from the flammable vapors
- Does not allow fuel to release vapors
- Separates the flames from the fuel surface, stopping burning process
- Cools the fuel surface and the surrounding areas
Foams are effective on Class B fires by
suppressing their vapors.
Class B fires are
fires involving flammable or combustible liquids
Flammable liquids can be divided into two categories:
- Hydrocarbons
- Polar Solvants
Hydrocarbons
By Products of crude oil or have been extracted from vegetable fiber
- Have a specific gravity less than 1.0
Examples of hydrocarbons
- Gasoline
- Diesel
- Heptane
- Kerosene
- Jet fuel (JP4)
Polar Solvents
Products that have been synthetically produced and are not found in nature.
Polar Solvents and water
They mix.
Polar Solvents are found in
dry cleaning products, paint thinners, nail polish removers, glue solvents, and even perfumes.
Examples of polar solvents
- Alcohol (inc. ethyl alcohol)
- Methyl tertiary-butyl ether (MTBE)
- Acetone
- Ethanol
- Paint thinners
When is foam not effective?
- Electrical fires (Class C)
- Three-dimensional Fires
- Pressurized Gases
- Combustible metals
Electrical Fires
Best extinguished using dry chem agents, carbon dioxide, or halon.
Three-dimensional Fires
Liquid fuel fire is being discharged from an elevated position or under pressure.
Best extinguished by controlling the flow of the liquid then using foam on spill.
Pressurized Gases
Best to cool the tank and let the gas burn until the flow can be controlled.
Examples:
- Propane
- Butane
- Acetylene
- Nitrogen
- Argon
Combustible Metals
Class D fires
- Aluminum
- Magnesium
- Sodium
- Potassium
Best extinguished with Class D Powder
Protein Foam
Intended for hydrocarbons only.
Types of Foam
- Protein Foam
- Fluoroprotein Foam
- Film-Forming Fluoroprotein (FFFP) Foam
- Aqueous film-forming foam (AFFF)
- Alcohol-resistant aqueous film-forming foam (AR-AFFF)
- Synthetic detergent foam
Fluoroprotein Foam
Add fluorochemicals to lower surface tension and allow foam to flow more freely.
Film-Forming Fluoroprotein (FFFP) Foam
Same as Fluroprotein foam with added chemical surfactants.
Excellent for subsurface injection
Aqueous film-forming foam (AFFF)
Use air-aspirating nozzles
Works by spreading a strong foam blanket over the fuel, smothering the fire. Also form vapor barrier
Alcohol-resistant aqueous film-forming foam (AR-AFFF)
Combo of foaming agents, synthetic stabilizers, fluorochemicals, and synthetic polymers
- For use on Polar Solvants
Most versatile foam (covers polar solvents and hydrocarbons)
Synthetic Detergent Foam
Work on Class A and Class B fires
Foam Proportioning Devices
Effectiveness of foam depends on proper proportioning and the ability to deliver the finished foam where it is needed.
Two principle ways to add foam to water:
- Induction (Venturi principle)
- Injection
Proportioning Devices
Inline eductors
Balanced pressure systems
Around the pump system
Foam nozzles
Inline Eductors
Most common type; Work on Venturi principle
Rules for eductors:
1. Have a set GPM flow rate (typical: 60-250 gpm)
2. Require adequate inlet pressures (180-200 psi)
3. Do not like back pressure (can handle 65% of inlet pressure)
Backpressure rules for eductors
- Nozzle must be fully open or fully closed
- No kinks in the hose between eductor and nozzle
- Do not elevate nozzle higher than eductor
- Don’t exceed hoselay length
- Keep pickup tube short. (no longer than 6ft)
- Keep eductor clean
- Flush eductor, nozzle, and hose for 5 min.
- Allow transit time of foam (20-40 seconds)
When determining pump discharge pressures, the ____________________ should be treated as the nozzle pressure.
Eductor Inlet Pressure
Around the pump systems use eductor on the discharge side of the pump. Advantages:
- Variable flow rate
- Variable pressure
- No back pressure restrictions
- No nozzle restrictions
Around the pump restrictions:
- Minimum pressure of 10 psi
- Important to flow water and foam at same time.
- Continually monitor proportioning valve to correspond with GPM flow
- Clean up is more difficult - all discharges need to be flushed
Foam Nozzles
Foam-aspirating nozzles use the Venturi principle and have the pickup tube connected to the nozzle.
Advantages of foam nozzles
- Deliver large amounts of finished foam
- Easy to operate
- Easy to clean
- No moving parts
- No additional foam equipment needed
Foam nozzles produce expansion ratio between ____ and _____, producing good-quality, low-expansion foam.
8:1 and 10:1
