Compressed Air Foam System - Foam Types

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, meaning the bubbles do not burst and give up their water quickly, and long duration. Wet foams, such as type 4 and 5, drain more quickly in the presence of heat .

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 compressed air foam, Dominic Colletti recommends utilizing a 0.5 cubic feet (0.014 m3) per minute to 1 US gal (3.8 L) per minute "air to foam solution" ratio, with a 0.5% class A foam proportioning rate. This would produce flow rates from a typical 1-3/4" inch hose of 120 US gal (450 L) per minute of foam solution and 60 cu ft (1.7 m3) per minute of compressed air. This air to foam solution ratio produces a wet, quick draining finished foam that will quickly knockdown flame and reduce fire compartment temperature. This ratio also allows for a higher relative foam solution (liquid) flow rate to help maintain the highest levels of firefighter safety possible. (The Compressed Air Foam Systems Handbook, Colletti 2005.)

While Colletti's claims for flows are not agreed upon by many industry experts, as exhibited at the CAFS symposium held in Rosenberg, Texas in February 2007. A panel there agreed that flows of 1 US gal (3.8 L) per minute foam solution in tandem with 1 cu ft (0.028 m3) per minute 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 cu ft (2.0 m3) per minute of air and 70 US gal (260 L) per minute of water is approaching the maximum limit or carrying capacity of that diameter hose (1.75 inches). (Texas CAFS Symposium February, 2007)