A NEW STIJDY, FUNDED BY THE DEPARTMEI\'T of Homeland Security's Assistance ro Firefighters Grants, is investigating d1e effectiveness, limitations, and potential safecy concerns of compressed air foam sys tems (CAFS) for s tructural fuefighting. CAFS use a designated mixture of water, Class A foam , and compressed air dlat is applied through a hose and nozzle to control a fire (photo 1). CAFS were originally used for wildland firefighting in dle early 1970s and then later gained popularity for fighting structural fires because of dleir many purported benefits, which in cluded faster knockdown time, rapid heat reduction, lowered potentiaJ for flare-ups, and reduced water use. Although used in various fire districts throughout dle world, CAFS technology and use have not evolved as fully as had been anticipated. Despite generally favorable reviews of the overall effectiveness of CAFS in extinguishing interior struc rural fires, questions remain about dleir efficacy compared to water, which is of particular concern given that compt"essed air foam (CAF) is more expensive than water. Further, there are safe£)' concerns (based largely on Limited anecdotal evi dence) associated with CAF, such as the potential for splash back, which might subsequently obscure vision and increase slip hazards and h e ightened hose kinking and rupture. AJdlough some independent research by individual fire districts and organizations exists, comprehensive and peer reviewed science is limited at present. Given the current interest in and concerns with CAP, a simultaneous, scientifi cally sound investigation of its positive and negative aspects