Heat and water accumulation in closed-circuit breathing apparatus: a technological challenge

A prototype closed-circuit self-contained breathing apparatus (SCBA) was evaluated against a standard 30-min open-circuit SCBA when worn by men performing heavy exercise on a motor-driven treadmill in hot and cold environments. The closed-circuit SCBA provided quality breathing air for a duration exceeding four times that available from the open-circuit system. Although the high temperature and humidity of the air provided by the closed-circuit system was somewhat irritating to the subjects, they are found to be an acceptable tradeoff in exchange for the increased duration of respiratory protection