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
Regular Protein Foams
-10 year shelf life
-Derived from animal protein
-Has a good heat stability
-Degrades quicker in storage than synthetic foam
Flouroprotein Foam
-20-25 year shelf life
-Combination of protein and synthetic foam
-Provides longer lasting vapor suppression
-May be made alcohol resistant which is effective for 15 minutes
Film Forming Fouroprotein Foam (FFFP)
-Long lasting heat resistance
-Capabilities of (AFFF) for quick knockdown
-Also available in alcohol resistant formulation
Aqueous Film Forming Foam (AFFF)
- Most commonly used foam
- Flourochemical surfactants reduce surface tension of water in foam one degree that a thin film is formed to spread across the fuel product
- Alcohol Resistant AFFF is commonly used on polar solvent
-AR-AFFF creates a membrane which separates the water in the foam blanket
-applied gently
-Aspirating nozzles are generally best for preserving the membrane
Low Energy Foam Proportioning System
-Operated by one of two basic principles:
-Venturi effect created by pressure of a water stream flowing through a restricted orifice inducts (draft) foam concentrate into water stream
-A pressurized proportioning device injects foam concentrate into water stream at a set ratio and as a higher pressure than the water flow
High-Expansion Foam
- Contain detergent base and low water content
- Provides less runoff and minimizes water damage
- Common Applications:
-Concealed space fire
-fixed extinguishing systems
-Class A fire
In-Line Foam Eductor
-Designed to be attached to pump panel discharge or connected in hose lay
-The inline eductor uses venturi principle to draft foam concentrate into water stream
-Foam becomes less viscous when heated
Guidelines to achieve properly proportioned finished foam on In-Line Foam Eductor
-Flow in gallons per minute through educator must not exceed rated capacity
-Discharge side of educator must not exceed 70 percent of educator inlet pressure
-Concentration will only be accurate if Inlet pressure at the eductor is correct (150-200psi)
-Low pressure will not create venturi
-High pressure concentration may be too rich, rapidly depleting resources
-Eductor properly maintained, run bucket of water through pickup tube for at least one minute
-Metering valves must be set to draw correct percentage
-Eductor should be no more than 6 feet above concentrate
-Nozzle and educator must have same gpm rating
Foam Nozzle Eductor
-Operates under same principal as in-line educator
-Eductor is built into the self-educting nozzle
-Requires that foam is available where the nozzle is operated
Self-Educting Master Stream Foam Nozzle
- Uses modified venturi design to draw concentrate into its water stream
- Pickup tube is located in the center bore of nozzles
- Deployed when flows exceed 350 gpm (capable of 14,000 gpm)
- Advantage is pressure drop is much lower (10 percent or less)
-allows for much greater reach capabilities - Jet ratio controller allows supply at a seperate location as far as 3,000 feet away (Supply master stream)
-proportions concentrate to 66.5%
-then further proportioned to 3% at nozzle
Installed In-Line Eductor Systems
- operates under same principles as portable in-line eductors
-only difference is it’s fixed - Bypass proportioner is installed to reduce friction loss
-a valve directs flow through second chamber to allow the switch from water flow to foam - Not effective on Class A foam operations
Around-the-Pump Proportioners
- Most common type of installed proportioners used in modern fire apparatus
- Open position valve allows 10 to 40 gpm
- Disadvantages:
-older models may only work with onboard tank water
-inability to pump both foam and water simultaneously - Prevention of excess foam use- close bypass valve when line is not flowing
Bypass-Type Balanced Pressure Proportioners
- Used on large mobile apparatus such as ARFF vehicle
- one of the most accurate methods
- Ability to monitor demand for concentrate and adjust
- Ability to flow water and foam simultaneously
-Has a foam concentrate line supplied by separate foam concentrate pump connected to each discharge outlet
Variable-Flow Variable-Rate Direct Injection Systems
- ability to proportion any flow rate or pressure with equipment’s design limits
- able to adjust to changes in water flow as nozzles are opened or closed
- compatible w/ high energy foam systems (CAFS)
- Operate off power supplied by the apparatus electrical system
-some larger units use combo of electric and hydraulic - Ratio controlled by speed of a positive displacement pump that inject foam into water flow
-Rates from 0.1 to 3 percent - Class A and Class B foam
-AR-AFFF not usable
-Drawback foam flowing in one discharge all discharges are foam
Variable-Flow Demand-Type Balanced Pressure Proportioners
- Pump/Demand system
-consists of variable speed mechanism driven electrically or hydraulically
-operates foam concentrate pump - Flow of concentrate matches the pressure demand
- water/foam can be discharged simultaneously
- Requires no flushing afterwards
Batch Mixing
-Simplest method of proportioning
-Only used in Class A foam concentrate
-Class A do not retain their foam properties when mixed with water for more than 24 hours
-AFFF will stay suspended in solution for extended period of time
High Energy Foam Generating Systems/CAFS
advantages/disadvantages
foam and air rates
- Introduce compress air into foam solution
- CAFS are designed to flow foam through preselected discharges
- Advantages:
-allows greater distances than ordinary foam/water streams
-adheres to fuel surface and resists heat longer
-hoselines weigh less - Disadvantages:
-price and maintenance costs
-may have eratic hose reaction
-Require additional training - Proportion rate of 0.1-1%
- 2 ft³/min of airflow per gallon/min of foam solution produces dry foam of up to 100gpm
-substantial amount of foam at 10:1 ratio - most use airflow rate of 0.5-1.0 ft³/min
-allows adequate drainage from the blanket to wet the fuel
Foam: Smooth Bore Nozzles
-Limited to application of Class A foams from a CAFS
-Provides effective stream with excellent reach
-oriface no greater than half of hose diameter
Foam: Fog Nozzles
- May operate fixed flow, selective flow, or automatic fog nozzles when applying a low expansion foam blanket
- Expansion ratio 2:1 up to 4:1
- most efficient w/ AFFF and Class A Foam
-AR-AFFF may be used on hydrocarbons
-not acceptable for fluorprotein foams - Not for incidents with polar solvents
- foam aeration attachments added to increase aspiration
Air-Aspirating Nozzle
-Induct air into the foam solution
-Only used with protein and Fluoroprotein concentrate
-Provide maximum expansion but reach is limited
-Larger and longer
Foam Application Techniques
Direct-application method
Roll-on method
Bank-down method
Rain-down method
Medium-and High-Expansion Foam Generating Devices
- 2 basic types
-Water aspirating and mechanical blower - Medium Expansion- 20:1 to 200:1
- High Expansion- 200:1 to 1000:1
- Water Aspirating
-Larger and longer
-Back portion of nozzle is open for airflow
-End of nozzle has screen that break up foam and mix with air - Mechanical Blowers
-only high expansion
-look very similar to smoke ejectors
-Blowers force air into the foam
-Well suited for incidents requiring total flooding they produce foam with very high air content
Foam Application Techniques:
Direct Application
-For Class A foam
-Applying finished foam directly onto burning material
Foam Application Techniques:
Roll-On Method
-Class B Foam
-Direct stream on the ground near front edge of burning liquid
-Foam will then roll across surface of fuel
-Use only for pool of liquid fuel on open ground
Foam Application Techniques:
Bank-Down Method
-Class B Foam
-Foam is directed onto a vertical surface and allowed to run down and spread across the pooled fuel product
Foam Application Techniques:
Rain-Down Method
-First two methods are impractical due to elevation
-Fire stream into the air above the fire, allowing the foam to gently rain down on surface of fire
-Incident involving aboveground storage tank
Foam: Environmental Impact
-Destruction of vegetation and aquatic life
-Biodegradability determine by rate at which bacteria can degrade foam
-Decomposition results in the consumption of oxygen
-No foam should be discharged into any body of water
-NFPA 1150 Standard on Foam Chemicals for Fire in Class A Fuels
NFPA 1150
Standard on Foam Chemicals for Fire in Class A Fuels
Durable Agents
- “gelling agents”
- Retain their fire retarding properties longer than Class A foam
- May be airdropped via tank or helicopter
- Will adhere to vertical structure surfaces up to 24 hours
- When used as extinguishing agent:
-ratio: 1:100
-Fireline: 1.5-2%
-Structural protection: 2-3%
