Control of Unconfined Vapor Clouds by Fire Department Water Spray Handlines

October 1987
DHHS (NIOSH) Publication Number 87-105

Use of water in emergency situations involving release of hazardous materials was discussed and a bibliography provided of major relevant technical articles. Topics discussed include prevention of vapor cloud formation, reduction of vapor clouds, control of vapor clouds, and preventing or controlling their ignition. The only feasible control technique which has evolved using water to prevent or control formation of a vapor cloud was to enhance water by foam liquid and apply as foam over the exposed surface. Special HAZ MAT foams have been studied and documented for such use. Success in reducing vapor clouds was obtained by covering hazardous material with a layer of water in the case of a small scale spill of carbon- disulfide (75150). While emulsification has been successful to some extent, this has mainly been in fixed systems. Vapor scrubbing or vapor phase reactions were not practical or effective except for anhydrous-ammonia (7664417) sorption by water sprays. Effectiveness of ventilation or barrier effects through air movement has been shown for control of vapor clouds in several studies. These methods have been viewed as impractical in some tests. The difficulty may be in determining what size cloud should be attacked in this way. There has been no success in using water spray handlines to prevent or control ignition unless they can extinguish the ignition source. Water sprays can reduce radiant heat exposures of fire fighters and protect against radiant burns. General guidelines were presented.