Safety evaluation of Self-Contained-Self-Rescures: Carbon dioxide absorption of SCSRS under heavy work load

The purpose of this study was to evaluate the safety of Self-Contained- Self-Rescuers (SCSRs) under a heavy work load. Three units, two chemical- oxygen (KO₂) types and one compressed-oxygen type, were evaluated by a breathing and metabolic simulator and by a human subject. The metabolic rate in the simulator tests was equivalent to light work; the human subject tests were at a heavy work load. With regard to the main physiological stressors imposed by SCSRs, it was found that the inhalation temperature under heavy work conditions was able to be estimated from the data of the light work condition; the breathing resistance had roughly the same relationship under both light and heavy work conditions. On the other hand, for the inhaled carbon dioxide, there was no correlation between the two conditions. It was found that some SCSRs experienced a rapid increase in inhaled carbon dioxide when the metabolic rate of the user exceeded the absorbent capacity of the units. In those cases, the user could not continue walking nor breathing through the unit. To ensure the safety of the user, we propose that the certification standards be changed to include evaluation of carbon dioxide absorbent capacity under heavy work load.