Rapport uit December 1996
http://www.usfa.dhs.gov/downloads/pdf/publications/tr-083-508.pdfU.S. Fire Administration/Technical Report Series
Class A Foam for
Structural Firefighting
(...)
IV. SUMMARY OF ADVANTAGES AND DISADVANTAGES
Advantages
The fire departments that are using class A foam and recent literature list many advantages in the use of class A foam over plain water, including the following.
1. Class A foam allows faster fire suppression and extinguishment than with plain water.
Firefighters report that fire knockdown often occurs more quickly with class A foam. This has been substantiated in both actual fireground operations and experimentation. Firefighters and incident commanders have reported some cases where foam outperformed plain water lines while, in other cases, the foam performance was considered equal to water. There were no reports of inferior performance.
Tests conducted by the Underwriters Laboratories for the National Fire Protection Research Foundation compared plain water streams against class A foam in a series of comparative tests and came to the same conclusion. Underwriters Laboratories conducted additional tests for the U.S. Army with similar results.
2. Class A foam increases efficiency and conservation of water supply.
The increased efficiency per gallon of water is most evident with CAFS. The difference in effectiveness
per gallon of water is estimated in the literature as high as 5 to 10 times over plain water for some applications. A CAFS engine with a 500-gallon water tank would have the equivalent fire suppression capability of a vehicle with a 2,500- to 5,000-gallon water tank.
Water supply is conserved because less gpm is needed per hoseline. The experimental use of CAFS in the City of Boston in 1992 showed that a 1,000-gpm pumper with a 700-gallon water tank, could operate a single CAFS 1-3/4-inch attack line from the tank water for approximately 10 minutes before needing to secure an additional water supply. With plain water the 700-gallon
tank would only be able to supply a 1-3/4-inch attack line for three to four minutes. The Boston firefighters estimated that the CAFS attack line had about the same capability to knock down the fire as the 1-3/4-inch line using plain water. This could provide a tactical advantage in situations where establishment of water supply is delayed.
Reduced water use was noted in several tests. With foam, less water will remain for run-off and associated water damage from firefighting operations and overhaul in a structure fire. The use of class A foam tends to reduce the amount of water that is needed to control and overhaul all types of fires, particularly where densely packed or compressed fuels are involved. However, the impact appears to be most significant in rural and wildland/urban interface firefighting, where the water supply may be limited to the capacity of the tank on the attack vehicle.
In theory, the reduced use of water could also be advantageous in lessening the contribution of fire suppression activities to building collapse, because the applied foam would weigh less than a comparable amount of water. This has not yet been documented in actual fireground operations,
nor in experimental studies.
3. Class A foam can be produced at a relatively low cost.
Class A foam concentrates are proportioned at rates between 0.1 percent and 1.0 percent. (This compares with class B foam concentrates which are proportioned at 3 percent to 6 percent.) At a rate of 0.3 percent, 1,000 gallons of class A foam can be produced with only 3 gallons of class A foam concentrate and 997 gallons of water; the estimated cost of the concentrate would be about $30 (assuming a cost of $10/gallon of concentrate). An equivalent amount of class B foam at 3 percent would require 30 gallons of class B foam concentrate and 970 gallons of water: at a cost of about $300 dollars (assuming the same cost per gallon of foam concentrate).
One fire department contacted for this report estimated that the cost of their class A foam concentrate
was probably offset by the savings in their use of diesel fuel resulting from reduced operating time on the fireground.
The lower cost of class A foam can reduce the cost of training for class B fires. Some departments
that could not previously afford to use class B foams for training are currently using class A foam to simulate foam application. In addition, class A foams are biodegradable and more environmentally friendly than class B foams, so less clean up is required after training.
4. Class A foam forms a protective blanket.
Like water or class B foam, class A foam extinguishes a fire by cooling, but it also has a secondary effect of separating the fuel from its oxygen supply by forming a vapor barrier. This blanket also insulates unburned fuels and exposures from radiant heat or direct flame impingement. This property is particularly effective in protecting exposures and preventing re-ignition after a fire has been knocked down.
5. Foam is visible during and after application.
Class A foam, especially CAFS, is visible during and after application. The visible foam allows firefighters to determine when an area has been adequately covered and when additional coverage
is necessary. This is especially useful in wildland/interface firefighting situations where structures must be protected along a large fire front, or in urban situations where an exposure building is threatened by radiant heat or direct flame impingement.
6. Foam clings to most surfaces and protects exposures much longer than plain water.
The ability of class A foam to cling to most surfaces provides advantages in reducing water run-off, helping to reduce water damage and aiding fire extinguishment. The clinging foam solution also aids in the protection of exposures, particularly vertical surfaces and sloped areas. This effect is greatest with CAFS, but can be significant with nozzle-aspirated class A foams as well. Foam can be applied to an exposure and left for a period of time before a reapplication is necessary. (Plain water generally requires a constant flow of water to provide exposure protection.)
In addition, the reduced surface tension of foam-enhanced water allows it to penetrate more deeply into class A fuels.
7. CAFS attack lines are lighter than plain water hoselines.
Attack lines that are used to deliver compressed air foam are significantly lighter and easier to handle than plain water handlines, because the product inside the hose is mostly air. The line weighs approximately half the weight of a regular hoseline of the same diameter.
The reduced weight and increased maneuverability can reduce firefighter fatigue and stress. Firefighters can easily handle larger diameter CAFS lines. (Nozzle-aspirated class A lines weigh approximately the same as plain water lines, because they contain the same amount of water.)
8. Foam use may help to preserve evidence of fire cause.
The wetting agent property of class A foams allows them to penetrate and extinguish deep-seated fires in combustible class A materials. This reduces the amount of manual overhaul necessary in the fire area. The fire scene may be better preserved for investigators to determine the fire cause because there is less disruption for overhaul and less damage caused by the impact of the hose streams.
The class A foam eventually evaporates or can be removed to allow for inspection and investigation.
9. Class A foam can be used on flammable liquid fires.
Early tests demonstrated that class A foams may be effectively used on some class B flammable liquid fires, although their relative efficiency as compared to class B foam concentrates has not been documented.
10. Class A foam aids wildland/urban interface attack
Class A and CAFS were originally developed for wildland firefighting and controlling interface
fires. Class A foam has been deployed from portable pumps, brush and fire engines, and dropped from aerial tankers and helicopters. The advantage of foam over plain water in the wildland/urban interface settings has been documented over many years.
11. Class A foam may provide long-term cost savings and reduced property damage.
The use of class A foams may lead to long-term cost savings in terms of property saved and resources deployed, over what would have been incurred with the use of plain water alone; however, this has not been conclusively documented.
The quick extinguishment and exposure protection afforded by class A foam and CAFS should lead to decreased total property damage from fires and from fire suppression activities. Departments using foam have documented saving property with foam that they believe could not have been saved using older, plain water firefighting tactics.
12. Firefighter stress and fatigue may be reduced.
The use of class A foam or CAFS may reduce physical stress on firefighters by contributing to faster fire suppression, reduced time to conduct overhaul activities, and faster turn-around time for companies involved in fire suppression activities. This factor is particularly applicable to CAFS, due to the lighter weight and easier maneuverability of the line.
