Compressed Air Foam System

A Compressed Air Foam System for hand hose, abbreviated CAFS, is a system used in firefighting to deliver fire retardant foam for the purpose of extinguishing a fire or protecting unburned areas from becoming involved in flame.

Description

Ron Rochna of the National Interagency Fire Center in Boise, Idaho defines a compressed air foam system as a standard water pumping system that has an entry point where compressed air can be added to a foam solution to generate foam … The air compressor also provides energy, which, gallon for gallon, propels compressed air foam farther than aspirated or standard water nozzles .

Typical components include a centrifugal pump, a water source, foam concentrate tanks, a rotary air compressor, a direct-injection foam proportioning system on the discharge side of the pump, a mixing chamber or device, and control systems to ensure the correct mixes of concentrate, water, and air .

It is proven that CAFS attacks all three sides of the fire triangle simultaneously. The foam blankets the fuel, thereby reducing the fuel’s capacity to seek out a source of oxygen. The CAFS solution adheres to ceilings and walls, more readily aiding in rapid reduction in heat. The opaque surfaces of the foam, as it adheres to walls and ceilings, shield the fuel source from radiant energy. (Brooks, 2005; Brooks, 2006)

* Also the term used for any pressurized water style extinguisher that is charged with foam(CAFS/AFFF/FFFP) and pressurized with compressed air.

History

The idea that water is not a perfect tool for extinguishment has been long noted, as by W. E. Clark (1991):The process of extinguishing fire by water is cumbersome and generally costly … the cost of installing water mains large enough for required flow, the installation and maintenance of fire hydrants, and the acquisition and maintenance of fire department pumpers, fire hose, and nozzles, make water a fairly expensive extinguishing agent … the use of water is hardly the ideal way to extinguish fire … there must be a better method waiting to be discovered (p. 75).

Liebson (1996) adds, "Water is an inefficient extinguishing agent. It requires the use of large quantities at costs both financial and physical. These costs are imposed on the firefighter and the community" (p. 5).

The use of foam additives to water for extinguishment dates back to an English patent in 1877 for a method to produce chemical foam (Liebson, 1991, p. xi). The British Navy experimented with agents foamed by means of compressed air in the 1930s (Darley, 1994) and the U.S. Navy was using compressed air foam systems (CAFS) in the 1940s for flammable liquid fires. By the 1960s do-it-yourself car washes were using CAFS with low pressure and small-diameter hoses and nozzles, which flowed about 4 gallons per minute (gpm) of solution and 4 cubic feet per minute (cfm) of compressed air, with a nozzle reach of about 40 feet (Rochna and Schlobohm, 1992).

In the mid 1970s the Texas Forest Service developed a water expansion system known as the Texas Snow Job. This pioneering Class A CAFS used a pine soap derivative, which was readily available as waste from local paper manufacturing industries, as a foaming agent mixed as 8 to 9 parts agent to 91 to 92 parts water, flowing up to 30 gpm. The duration was limited by the use of compressed air cylinders rather than compressors. By the mid 1980s, research by the U.S. Bureau of Land Management led to modern design features of rotary air compressors, centrifugal pumps, and direct-injection foam-proportioning systems (Fornell, 1991; IFSTA, 1966). CAFS received national attention in 1988 during the Yellowstone Park wildfires when the four-story Old Faithful Lodge was successfully protected by blanketing it with compressed air foam (Darley, 1994).

In the Spring of 1994 a compressed air foam demonstration vehicle manufactured by Darley, AKA W.S. Darley & Co., was driven from coast to coast in North America. The purpose was to spread the word about CAFS and display this relatively new technology to the United States and Canadian fire service. This AutoCAFS demonstration vehicle was driven and operated by Troy Carothers who was involved with the initial design and assembly of the Darley AutoCAFS product. Carothers is now the Darley AutoCAFS Manager and oversees all aspects of CAFS development for Darley Co. This demonstration vehicle concept has continued annually since 1994.

The overview and historical data propelled the research on to a closer look at the claims made for CAFS and the reasons behind them.

Foam types

CAFS is able to deliver a range of useful foam consistencies, labeled from Type 1 (very dry) to Type 5 (wet), which are controlled by the air-to-solution ratio, and, to a lesser extent, by the concentrate-to-water percentage. Type 1 and 2 foams have long drain times (i.e., the bubbles do not burst and give up their water quickly) and long duration. Wet foams, Type 4 and 5, drain more quickly in the presence of heat .

Advantages

Versatility

A major advantage of using CAFS is having the unique ability to produce a wide range of foam qualities or foam types to provide the most appropriate foam response to individual fire situations … This gives the fire officer the advantage of custom tailoring the best foam type for the tactical use and fire problem at hand .

After testing a dry Type 2 foam in several situations, Johnny Murdock notes "The emerging consensus is that the dryer foams (Type II; maybe Type I) should be used to suppress vapors, protect unburned structures, build wildland fire lines involving unburned fuels; … and that structural fire suppression requires a wetter foam (Type IV or Type V); and that both structural and wildland overhaul require Type V foam."

For structural firefighting with CAFS, Dominic Colletti recommends "A 1-3/4-inch hoseline flowing 80 gpm and 80 scfm (standard cubic feet per minute) with Class A foam proportioning at 0.3 percent will produce a wet, quick draining finished-foam that has excellent flame knockdown."

While Colletti's claims for flows are not agreed upon by many industry experts as exhibited at the recent CAFS symposium held in Rosenburg, TX in February 2007, it should be noted that same panel agreed flows of 1 GPM foam solution in tandem with 1 CFM air produce the most effective blanket. It was further agreed that the maximum combination of air flow mixed with foam solution flow out of a 1-3/4" line under normal pump pressures of 100 - 125 PSI could not physically exceed a total of 140 -150. In other words the simultaneous flow of 70 CFM of air and 70 GPM of water is approaching the maximum limit or carrying capacity of that diameter hose line (1.75 inches). (Texas CAFS Symposium February, 2007)

CAF Additive

To take the full advantage of Compressed Air Foam technology, special CAF Additive was developed recently. NAFFCO CAF Additive gives better foam blanket formation and adhesion to vertical surfaces. The special structure of foam obtained with new generation CAF additive gives fast fire suppression in comparison to conventional AFFF.

Water Can Conversion

APW fire extinguishers are commonly converted into makeshift CAFS extinguishers by drilling two 1/8-1/16 inch holes in in the pickup tube. The unit is then filled with 1.5 gallons of water and Class A foam, AFFF, FFFP or commercial detergent is added to the water in a 1% ratio for class A fires and a 3%-6% ratio for Class B fires. Typically, the tip of the smooth-bore application nozzle is then cut off to allow the foam to properly expand. Keeping the nozzle will result in wetter foam but and longer range. Cutting the nozzle will result in an expanded, dry foam but will lack the range of the standard water nozzle. CAFS extinguishers can also be fitted with air aspirators (commonly used on AFFF and FFFP foam extinguishers) which will result in a more expanded foam but will lack the 'staying power' or heat resistance of non-aspirated foam with does not break the bubbles.

ource

* [http://www.usfa.dhs.gov/downloads/pdf/tr_98rt.pdf Technical Report 98: Compressed Air Foam Systems in Limited Staffing Conditions] —- United States Fire Administration, Department of Homeland Security, United States Government

External links

* [http://snuffer.com/compressed-air-foam-systems.html More info on Compressed Air Foam Systems]
* [http://www.fomtec.com Foam Concentrates for CAFS]