The Bureau of Mines subjected three commercial compressed-oxygen self-contained self-rescuers to a series of laboratory treatments designed to simulate various environmental conditions in underground coal mines. The environmental treatments consisted of extremes of temperature and of shock and vibration. The tests were designed to predict the ability of the self-rescuers to withstand those environmental stresses without causing a decrease in wearer protection. A critical concern was internal damage to an apparatus that would cause it to malfunction or seriously degrade its performance without any obvious external signs. Although the three compressed-oxygen units are not as sturdy as the chemical oxygen self-rescuers tested previously, they performed reliability after treatments on treadmill tests with human subjects and on machine tests using a breathing and metabolic simulator. Serious damage was caused by both the heat treatment of 71 degrees c, and in the shock treatment. When physical damage is obvious, a complete refurbishing of the damaged self-rescuer is recommended.