Flashcards in Foam Concentrate Technology Deck (45)
The resulting finished foam ...
... extinguishes and/or prevents fire by the following methods:
Separating - Creates a barrier between the fuel and burning vapors
Cooling - Lowers the temperature of the fuel and adjacent surfaces
Suppressing - (sometimes referred to as smothering) Prevents the release of additional flammable vapors, access to oxygen in the atmosphere, and therefore reduces the possibility of ignition of resignation
As water in the finished foam blanket ...
... releases (drains), the foam blanket becomes less effective as a vapor barrier and/or heat shield.
The rate at which a foam blanket reduces in effectiveness is proportional to the rate at which its water drains.
Mechanical type foam concentrates ...
... in use today must be proportioned (mixed with water) and aerated (mixed w/air) before they can be used
Liquid found in a foam storage container before the introduction of water
Mixture in the proper ratio of foam concentrate and water before the introduction of air
Device that mixes foam concentrate in the proper ratio w/water
Completed product after air is introduced into the foam solution and after it leaves the nozzle or aerator
Class B foam concentrates ...
... designed solely for hydrocarbon fires (such as regular fluoroprotein and regular AFFF) will NOT extinguish polar solvent (alcohol type fuel) fires regardless of the concentration at which they are used
However, foam concentrates that are intended for polar solvents may be used on hydrocarbon fires
Foam expansion ...
... refers to the increase in volume of a foam solution when it is aerated
Low Expansion Foam
Air/solution ratio up to 20 parts finished foam for every part of foam solution (20:1)
Medium Expansion Foam
Most commonly used at the rate of 20:1 to 200:1 through hydraulically operated nozzle style delivery devices
High Expansion Foam
Rate is 200:1 to 1,000:1
Freezing and thawing ...
... shall have no effect on UL listed foam concentrate performance
Compatibility w/Other Extinguishing Agents
AFFF, FFFP, and fluoroprotein foams are all compatible w/carbon dioxide, halon substitutes, and dry chemical agents and may be simultaneously discharged w/them
Also known as Multi-agent attack
Class A foam concentrates require ...
... U. S. Forest Service approvals from the U. S. Department of Agriculture
A short drain time means that the foam blanket holds water and provides an insulating foam layer for an extended period before the water releases
Elements affecting the drainage process
- Fuel temp
- Heat of the fire
- Size of the flame front
- Ambient air temp
Foam Concentrate Types
Some foam concentrates are thick and viscous. These concentrates are typically AR-AFFF, 3% to 6% or 1% to 3% and produce finished foam that can form tough, heat resistant blankets that drain slowly when proportioned at higher ratios of water and concentrate
Thinner concentrates are generally found in the nonalcohol-resistant (AFFF, FFFP, and fluoroprotein foam) or Class A Foam
High Expansion Foam Concentrates
Used from 1% to 2.5% concentrations to produce large volumes or finished foam for flooding confined spaces
Class A Foam Concentrates
Wetting agents (non foaming, ionic, and nonionic surfactants) added to water will improve its absorption into Class A materials.
Class A foam concentrate is a formulation of hydrocarbon surfactants. The ionic and nonionic surfactants help reduce water's surface tension in the foam solution
Reducing water's surface tension ...
... provides better fuel penetration of the water, thereby increasing its effectiveness
Surface Tension Reduction
The effect of a surfactant on the water/concentrate foam solution allows water to spread more rapidly over the surface of Class A fuels and penetrate organic fuels
Aeration of the water/concentrate foam solution into a volume of bubbles that is greater than the volume of the solution.
Water quality, aeration method( (nozzle, compressed air, airdrop altitude), concentrate ratio, and concentrate formulation all affect the obtainable expansion ratio
Amount of liquid that drains from the bubble mass to wet and/or penetrate the Class A fuel is affected by the expansion ratio
Small bubbles of a consistent size are best for the development of long lasting finished Class A foam that can adhere to surfaces (horizontal, vertical, and overhead)
Large bubbles tend to break down more rapidly and release more liquid to wet and and penetrate Class A fuels
Class A foam does not adhere to hot, vertical fuel surfaces that are in excess of 212 degrees F
Characteristic of Class A foam to remain on and in the fuel, reduce the fuel temp, and increase the fuel moisture content.
*Air temp, wind movement, fuel's latent heat, and the amount of heat present affect retention time
Refers to a liquid's thickness or ability to flow.
High viscous liquid concentrates are very thick and may be difficult to proportion through some types of foam concentrate pumps.
Low viscosity are very thin and pour easily.
Temperatures affect viscosity. Class A foam concentrates become more viscous when cold and less viscous when heated
Class A foam drain times increase w/an increase in the proportioning ratio.
A rich concentrate/water mix ratio (using a higher proportion of foam concentrate than normal) produces thicker, richer foam that drains slower than a lean ratio (using a lower proportion of foam concentrate than normal)
Most foam nozzles ...
... produce more stable finished foams at a 1% concentration than they do at 0.4% to 0.5% concentrations
*Greater than 0.5% w/standard fog nozzles does not appear to increase fire-fighting performance
Fire Attack and Overhaul w/Standard Fog Nozzles
0.2% to 0.5% foam concentrate
Exposure Protection w/Standard Fog Nozzles
0.5% to 1% foam concentrate
Most Operations w/Air Aspirating Foam Nozzles
0.3% to 1% foam concentrate
Most Operations w/Compressed Air Foam System
0.2% to 0.5% foam concentrate
Class B foam concentrates ...
... are manufactured from either a synthetic or protein base.
Protein base are derived from animal protein
Synthetic is derived from fluorosurfactants
Protein based foam degrade in 2 to 8 days
Synthetic degrade in 20 to 40 days
Effective Class B Characteristics
- Water retention
- Finished Foam Life
- Heat Resistance
- Multipurpose Use
- Knockdown Speed and Flow Characteristics
- Fuel Resistance
- Vapor Suppression
- Alcohol Resistance
- Quarter Life
*Most finished foam breaks down near or over 212 degrees F
**May become ineffective at fuel temps near or over 150 degrees F
***Polar solvent fuels (alcohols, ketones, and esters) are mixable (miscible) w/water
Class B Proportioning
Hydrocarbons - 3% (3:97 ratio)
Polar Solvents - 6% (6:94 ratio)
High expansion foams are used between 1% to 2.5%
Once the fire is extinguished ...
... finished foam consumption is only effected by the latent heat of the fuel, weather conditions, and finished foam's natural drainage rate
Regular Protein Foam
Concentrate is derived from naturally occurring sources of protein such as hoof, horn, or feather meal
Concentrates are oleophobic (oil shedding) and well suited for sub-surface injection: a process by which foam solution is pumped into the bottom of a burning petroleum tank and then floats to the top to form a fire extinguishing foam blanket
Fluoroprotein foam concentrates ...
... can be formulated to be alcohol resistant by adding ammonia salts that are suspended in organic solvents. Alcohol resistant fluoroprotein foam concentrate maintains its alcohol resistive properties for about 15 min
Is the most commonly used foam concentration today
AFFF is completely synthetic. It consists of fluorochemicals and hydrocarbon surfactants combined w/high boiling point solvents and water
When AFFF/FFFP is applied to a hydrocarbon fire ...
- Air/vapor excluding film is released ahead of the foam blanket
- Fast moving foam blanket moves across the surface and around objects, adding further insulation
- As the aerated (7:1 to 20:1) foam blanket continues to drain its water, more film is released giving finished foam the ability to "heal" over areas where foam blankets are disturbed
Are designed to mix with the fuel, breaking it into small droplets and encapsulating them. The resulting emulsion is rendered nonflammable