The increasing use of class A foam systems by urban and suburban fire departments for structural fire suppression has created a demand for information on this technology.  While class A foams have been used extensively by wildland and rural fire departments, their application to structural fire suppression is a recent trend.  This report discusses the use of class A foaming agents in conjunction with water for fire suppression (conventional or nozzle-aspirated class A foam systems); it also provides additional information on the use of class A foam agents with water and compressed air (compressed air foam systems, or CAFS)

Many fire departments have conducted their own field testing of class A foam to evaluate its effectiveness in structure fires.  Several departments have attempted to adapt class A foam equipment that was originally developed for wildland firefighting for structural firefighting operations.  Many benefits of class A foam have been reported, including quicker fire extinguishment, faster overhaul time, less damage to buildings, and reduced fatigue on firefighting personnel due to quicker mop-up after the fire is out.  Additional advantages reported with CAFS include the ability to maneuver attack lines easily and the ability to extend available water supply for a longer period of time.  Exposure protection is greatly enhanced with class A foam.

This report begins with a general overview of nozzle-aspirated class A and compressed air foam systems.  It then discusses hands-on evaluations by several fire departments that are currently using class A foam systems in structural fire suppression or wildland/urban interface fire protection.  These departments were contacted to provide a candid overview of their experience with class A foams and/or CAFS.  In all cases, these departments view class A foam and CAFS as additional tools which increase the efficiency and effectiveness of their fire suppression operations.  Reported advantages and disadvantages in the use of class A foams and CAFS in structural firefighting, both from field experience and from recent fire protection literature, are included in this report.

Recent studies conducted by Underwriters Laboratories in cooperation with the National Fire Protection Research Foundation and the U.S. Army Fort Belvoir Research, Development, and Engineering Center compared the use of plain water, nozzle-aspirated class A foam, and CAFS for the extinguishment of class A fires.  The experiments showed that nozzle-aspirated class A foam and CAFS generally extinguished the experimental fires more quickly and used less water than plain water extinguishing methods; though in some cases plain water was shown to be equally effective.

The use of compressed air foam systems (CAFS) for structural firefighting was previously evaluated by the United States Fire Administration in Technical Report 074 of the Major Fires Investigation Project in 1993.  That report,  “Compressed Air Foam For Structural Fire Fighting: A Field Test; Boston, Massachusetts,” highlighted the experimental use of a class A compressed air foam system by the Boston Fire Department’s Engine Company 37 in 1992-93.  The field test indicated some operational advantages provided by CAFS and encountered some shortcomings in retrofitting the existing apparatus.  The Boston test showed that more information is needed to be gathered to determine the extinguishing capabilities and conservation of water supply when using CAFS in an urban environment.