Ch. 14 Foam Equipment and Systems Flashcards
Reasons for Increase in Use of Foam
-Magnitude and frequency of hazardous material incidents
-Newer foam concentrates are more easily used
-Improvements in design of foam proportioning units
-Help reduce water usage
Principles of Foam
- Mechanical foams-
-Most common used
-Must be proportioned (mixed with water) and aerated (mixed with air)
-Foam concentrate, water, and air must be educted or injected in correct ratio - Foam concentrate- Raw foam liquid in its storage container
- Foam proportioner- Injects correct amount of foam into water stream
- Foam solution- Mixture of foam and water before introduction of air
- Foam- Completed product after air is introduced (finished foam)
Class B Fuels
Hydrocarbons- Oil, gasoline, benzene, kerosene, petrol based and have specific gravity less than 1
-Class B foams used on hydrocarbons
Polar Solvents- Alcohol, acetone, ketone, have specific gravity greater than 1
-known as miscible liquids, mix with water, use of alcohol-resistant foam (AR-AFFF) is needed
Foam Proportioning
-The act of mixing of water and foam concentrate to form foam
-proportioned THICK for exposures/fire breaks, THIN for easier penetration to surface of fuel
-can be mixed with fresh or salt water
-Must be proportioned at percentage specified by manufacturer
-Mix with 94 to 99.9 percent water
-3 percent foam is 3 parts foam 97 parts water
-Proportioned 4 ways
-Induction -Batch mixing
-Injection -Premixing
Foam Proportioning:
Induction
-Uses the pressure of water stream to induct (draft) foam concentrate
-Passes stream of water through a venturi device
-Uses pick up tube to pick up foam from container
Eductor- portable proportioning device that injects foam into water device
Pick up tube- solid or flexible tube to transfer foam from container to eductor
Foam Proportioning:
Injection
-Uses external pump to force foam concentrate into fire stream
-Most common in apparatus mounted or fixed fire protection system
Foam Proportioning:
Batch Mixing
-Foam concentrate is poured directly into a tank of water
-Commonly used with class A foam
-Class B foam tank must be circulated to ensure proper mixing
-must be thoroughly flushed after use
Foam Proportioning:
Premixing
-Premeasured portions of foam and water are mixed in a container
-Used with portable and wheeled extinguishers
-Discharged from pressurized tank using compressed air
-Once used, must be flushed and refilled before used again
How Foam is Stored
- Pails
-5-gallon plastic pails
-Easily stored on apparatus
-Remain airtight
-Educted directly from pail - Barrels
-55-gallon plastic barrels
-Bulk storage - Totes
-275-gallon container
-ARFF, wildland, or industrial facilities - Apparatus Tanks
-Have foam concentrate tanks piped directly to system
-Municipal range from 20-200 gallons
-Foam pumper or tenders may carry 8,000 gallons or more, must be air tight
-Smaller foam concentrate tanks located above the fire pump
-Larger tanks may be directly adjacent to the apparatus water tank
Class A Foam
-Use of structure, wildland, coal, tire storage, and other fires
-Better penetration/effectiveness than water
-Hydrocarbon surfactants- reduce the surface tension of water in the foam
-May be used with fog, aerating nozzles, and medium/high expansion devices, and CAFS w/ most nozzles
-Shelf life of 20 years
-Direct skin contact should be avoided (Corrosive effect)
-Minimum flow rate for water
Class A Proportioning
-Class A may be mixed with percentages as little as 0.1 to 1.0 percent
-Most foam nozzles produce stable foam at 1.0 percent
-Fire attack and overhaul with fog 0.2 to 0.5 percent
-Exposure protection with fog 0.5 to 1.0 percent
-Any application with air aspirating nozzle 0.3 to 0.7 percent
-Compressed air 0.2 to 0.5 percent
Application of Class A Foam
Application rate- Refers to minimum amount of foam solution that must be applied to fire, per minute, per square foot
Areas that require maximum penetration- Wet foam will penetrate class A fuels
Vertical surface- Dry foam forms a rigid coating that adheres well
Surface of fuel- Ability to cling and penetrate the surface of a fuel
Class B Foam
-Flammable and combustible liquids
-also used to suppress unignited vapors
-Consist of synthetic or protein base
-Synthetic foam is made of fluorosurfactants (20-25 years)
-Protein foam is made from animal protein (10 years)
-Protein foams are considered safer
-Mil-spec can be mixed at any time with no adverse effect
-brands of foam should NOT be mixed together except when mixed together immediated before use with similar types
Class B Proportioning
-Class B foams are mixed in proportion from 1 to 6 percent
-The correct proportion is found outside of each container
-Hydrocarbons are normally 1 to 3 percent
-Polar solvents are 3 to 6 percent
Foam Expansion
- The method used to aerate foam will create varying degrees of expansion based on:
-Type of foam concentrate used
-Accurate proportioning of foam to solution
-Quality of the foam concentrate
-Method of aeration - Low foam expansion 20:1
- Medium foam expansion 20:1 up to 200:1
- High foam expansion 200:1 up to 1000:1
Rates of Application
- Rate foam is applied depends on several variables
-Type of concentrate
-Whether or not fuel is on fire
-Type of fuel involved (hydrocarbon vs. polar solvent)
-Whether fuel is contained or uncontained - Before you start application of foam, ensure sufficient amount of foam and equipment are available to achieve objective
- Application should continue till extinguishment is complete from uphill and upwind
- Polar solvents may require different application rate based on type of solvent
- To calculate the application rate available from specific nozzle
-Divide flow rate by the area of fire250 gpm nozzle on 1,000 sq ft fire
250 gpm/1,000 sq ft = 0.25 gpm per ft
NFPA 11
- Standard for Low, Medium, and High-Expansion Foam
- Outlines the variables invloved and application rate requirements for many possible scenarios
