WHAT’S ALL THE TALK ABOUT CLASS A FOAM?
The latest buzzword in fire suppression being heard at eonferences and meetings is “Class A Foam.” Members of the fire service are asking questions such as, Will it work? Does it work on structural fires as well as wildland fires? Is it more effective than water? What equipment do we need to use Class A foam? How much do the foam and equipment cost? Will it help our department’s problem of low manning levels?
The best sources of information for a new product such as Class A foam are its manufacturers and the fire service people who have researched and experimented with it. At least four companies manufacture the foam and four others the proportioning equipment used with it.
Fire departments in Boise, Idaho; Fort Worth, Texas; New Brighton, Minnesota; Tucson, Arizona; and Springfield, Illinois and the California Division of Forestry at Davis are experimenting with and testing this product. Flow rates, methods of application, and the differences between straight-injection systems and compressed air foam systems are among the aspects being evaluated.
The Northwest Fire District in Tucson, Arizona, recently ran several structural test fires during which Class A foam was compared with water. The fires were conducted in rooms of the same size using the same fuel load, ignition factors, preburn time, fire crew, nozzle, and flow— which was 125 gpm at 100 psi nozzle pressure. Although CO levels measured the same with water and foam, the foam resulted in quicker knockdown time, lower steam production, and less reignition. The smaller amount of steam produced when using the foam did not drive the firefighters to the floor and allowed better visibility, enhancing the safety of the crew and any victims who might have required rescuing. Twenty-five percent less water wTas needed with the Class A foam attacks.
Many fire departments are experimenting with Class A foam on structural fires; some are using it regularly. A major benefit is that less water is used to knock down a fire, since it is expanded into foam. The foam coating also reduces the effect of heat on unburned surfaces, since the entrapped water adheres to the surface. The foam coats the fuel—for example, in the case of wallpaper, it excludes air and reflects heat so that the wallpaper does not give off flammable vapors. The water in the foam layer at die fuel interface absorbs heat, whereas straight water application could ricochet or run off the surface.
Using Class A foam when advancing down a hallway coats the surfaces and reduces rollover, preventing it from developing into flashover. The foam’s surfactant properties greatly reduce the need for overhaul, and when used during overhaul, the foam reduces rekindle possibilities, especially in stuffed furniture, bales, or mattresses. It can be put in an air-pressurized water (APW) extinguisher for small overhaul jobs and can help protect exposures since it adheres and coats.
WHAT IS CUSS A FOAM?
There seems to be some confusion about whether Class A foam is a retardant, a surfactant, or a wetting agent. Class A foam is a foam to be used on Class A or ordinary combustibles that often have a wood base or leave an ash. Although it retards fire spread, it does not reduce the combustibility of the material or have a long-term effect. It loses its retardant effect in three to five hours.
Class A foam, by virtue of the fact that it is a chemical additive that decreases the surface tension of the water with which it is mixed and allows the water to spread and penetrate more effectively, is a surfactant. It is not, however, wet water, since wet water does not foam; also, Class A foam has a lower surface tension than wet water.
As a retarding surfactant, Class A foam cools, penetrates, and coats. The foam can be produced in a light or heavy consistency. The heavier it is, the less penetrating the blanket. When mixed in proportions as low as 0.1 percent or one gallon per 1,000 gallons of water, Class A foam is effective. Its water component basically is applied at the same rate as water, but since it is a foam solution, it extinguishes the fire faster and with less water due to its ability to reduce surface tension and its expansion ratio. Class A foam discharged through a regular fog nozzle can be expanded from three to five times. This means that five gallons of water mixed with five ounces of Class A foam concentrate can be expanded to a finished foam volume of between 15 and 25 gallons. The varying expansion rate is due to the amount of aeration that takes place with different manufacturers’ nozzles.
CLASS A FOAM
METHODS OF PRODUCTION
Class A foam is produced in two ways. The first method—sometimes referred to as a low-energy foam system-uses the movement of the solution through the hose to draw air into the foam solution, such as in the case of an aspirating nozzle. The second method—called a high-energy foam system, or more commonly, a compressed air foam system (CAFS) — uses the introduction of high-pressure air and solution into the hose.
The ideal mix for a CAFS is believed to be one cubic foot of air per minute for each gallon of foam solution. Thus, a 125-gpm foam line needs 125 cfm of air. This can mean a large, expensive air compressor. A high-energy system has greater discharge distance or reach and uses less foam concentrate, since proportioning rates are less. These units produce a smaller, more uniform bubble, leading to a longerlasting foam. The hoseline also is lighter due to the large amount of air mixed with the foam solution. A significant amount of energy has been added, however, and care must be taken to ensure safety. If for any reason foam eduction into this line or the water supply ceases, the hoseline will contain only air and water or air and foam, creating a violent nozzle reaction.
MAKING A FOAM SOLUTION
Class A foam concentrate can be added to the apparatus water tank and delivered through standard fog nozzles. Foam delivery can be improved by adding an aspirating nozzle. The foam concentrate must be mixed in proper proportion, however, and it may be difficult to achieve the correct proportion when using this mixing method. Furthermore, pumping and maintenance problems—such as the need to flush the pump, and leaking valves—can result from putting the foam directly in the apparatus water tank.
A more common and better approach to making Class A foam is to use a venturi eductor and a small container (such as a five-gallon bucket or pail) of foam concentrate with either the fog or aspirating nozzle. When using this method, it is very important that the eductor and the nozzle have the same capacities; otherwise foam concentrate proportioning will be inaccurate and affect the foam’s effectiveness, especially at low concentration rates.
Class A foam also can be made by using proportioner and injecting measured quantities of foam into the pump discharge. The accuracy of the proportion can be assured by using flowmeters to measure the varying flows and to adjust the delivery of the foam concentrate. Class A foam applications can be further improved by injecting compressed air into the foam solution. However, it is best to use a direct-injection foam proportioner for the foam concentrate whether using a low-energy aspirating nozzle system or a high-energy CAFS. Injection always should be on the discharge side of the pump from the foam concentrate tank to ensure foam delivery to the nozzle.
As is the case with all new technology, Class A foam requires additional testing and experimenting before all of its qualities and uses can be determined. The foam already has proven effective for wildland fires. We should keep open minds and pursue innovative ways to explore other avenues for its use.