Compressed air foam systems
International Manager of Foam Education
New Brighton, Minnesota
Regarding “Compressed Air Foam Systems and Fire Hose” (Fire Engineering, July 1996), author Dominic J. Colletti and readers should read Foam Applications for Wildland and Urban Fire Management, Volume 7, No. 2, September 1995. The article “CAFS Rated Hose: Yes or No?” by Lois P. Sicking addresses the issue of compressed air and its effect on fire hose.
Sicking evaluated fire hose constructed to the U.S. Department of Agriculture Forest Service Specification 5100-186 or 5100-0187, typically single-jacketed cotton or synthetic-jacketed, rubber-lined (CJRL) and nonlined one-inch and 112-inch attack hose, typically used in all wildland operations and rated for a 450-psi working pressure. It can be used for any water or foam application, including CAFS, and maintains firefighter safety. The author states that pressure is pressure, whether created by a liquid or a gas.
After the Fire Equipment Manufacturers Association (FEMA) issued the safety warning, some wildland firefighters were concerned about the need to use only “CAFS-rated hose.” Typically, CAFS hoselines are operated at a pump discharge pressure of 75 to 150 psi, substantially below the working pressure of 450 psi for forestry hose constructed to USDA Forest Service specifications. In addition, there have been no “pulsations” or water hammer noted with the CAFS use of forestry hose when the typical CAFS unit is operated.
In the incidents in which forestry hose has failed when used with a CAFS system, the hose also would have failed with water alone. In addition, an informal survey of agencies using CAFS [U.S. Bureau of Land Management, Fish and Wildlife Service, Forest Service, Los Angeles County (CA) Fire Department, Phoenix (AZ) Fire Department, and others] did not find any unusual problems with fire hose using CAFS. This survey was made in the western United States where more than 250 CAFS are used in all branches of the fire service, including the telescoping waterways in the Phoenix Fire Department.
I am baffled that FEMA is concerned about air in fire hose and has issued a safety notice. Air is always in the hoseline at the same psi as the water when a dry line is charged. That is one reason the water nozzle is opened prior to beginning the attack–to bleed the air out! Anyone who has worked a charged water line is well aware of the dangers and risk, such as pinched hands and fingers and LDH couplings uncoupling, when hoselines are charged with plain water.
Colletti`s statement regarding the minimum design requirement for a CAFS used in structure and wildland interface fires and its fire hose incompatibility must be restated to say:
Fire hose used with a CAFS must not be subjected to pressures exceeding its designed rating. Pressure is pressure–be it hydraulic or pneumatic. If the hose is rated at 250 psi, it will perform no better or worse with CAFS. Of all the departments using CAFS, none have reported hose failures.
A CAFS will open in “no” more time than it takes to flow plain water. This issue involves firefighter safety.
A CAFS will separate valve air injection at each outlet that is desired to use air. This permits the operator to select any type of nozzle or aspirating foam generator on any outlet without interfering with the performance on another outlet. This is a critical safety item. CAFS is just another tool that does not fit all the suppression and presuppression tasks. It is common to use a CAFS handline and a medium-expansion foam generator at the same time to protect structures on an urban interface or vehicle fire.
Motionless mixers (static mixers) are not required on all CAFS outlets! Compressed air is best used as a fire stream delivery enhancer on fire attack lines. For a successful direct attack on Class A fire, it is not advisable to flow a self-insulating stream of bubbles. You want a high-velocity stream of small bubbles (films) with a large surface-to-mass ratio to maximize heat absorption. Master streams most of the time require a motionless mixer as well as a stream straightener to permit optimum stream delivery performance. Properly designed motionless mixers reduce total flow capabilities and add needless costs.
An automatic safety control that shuts off air when foam solution is not flowing is not necessary. A major feature of CAFS is that compressed air also operates jack hammers, air bags, and other rescue tools. Major departments such as Los Angeles County deliver compressed air through fire hoses to operate pneumatic rescue devices. Again, there is no history of a fireground problem of slug flow (air and water only) occurring on current apparatus. This monitoring device is an extra cost that is not warranted. Check with the hundreds of departments using CAFS on their first fire apparatus that do not have this control device! Failure to fill foam reservoirs after the last use is the only problem that has occurred, and this is an operator problem.
For free copies of all issues of Foam Applications for Wildland and Urban Fire Management, contact: Program Leader, Fire Management, USDA Forest Service Technology and Development Center, 444 East Bonita Avenue, San Dimas, CA 91773-3198.