Physiologic Basis for CO2 Limits Within Semiclosed and Closed-Circuit Underwater Breathing Apparatus
Technical rept. Feb-Jun 2000
NAVY EXPERIMENTAL DIVING UNIT PANAMA CITY FL
Pagination or Media Count:
Semiclosed- and closed-circuit underwater breathing apparatus UBA incorporate a canister filled with carbon dioxide CO2 absorbent material. As the absorbent becomes expended, the CO2 level within the breathing loop will rise. Currently, CO2 absorbent canisters are considered expended when the effluent CO2 is 0.5 Surface Equivalent Value SEV. In the past, this value often represented the threshold between the linear and the exponential rise in effluent CO2. The 0.5 SEV limit was used to reduce the divers risk for experiencing excessive levels of CO2. However, with advances in absorbent canister design, this value may be overly conservative. Because the overall respiratory load of a UBA can compound the effect of the inspired CO2, the improved breathing performance of some current UBAs also warrants reevaluating the current limit. This literature review specifically looked at low levels of CO2 affecting work and mental performance, nitrogen narcosis, decompression sickness and central nervous system CNS oxygen toxicity to determine if the breakthrough limit could be changed.
- Stress Physiology
- Life Support Systems