Six-Hour No-Decompression Diving With 40% Oxygen/60% Helium

U.S. Navy Special Warfare divers frequently perform long-duration, multilevel dives while breathing air, 100 oxygen, or nitrogen-oxygen mixtures in varying combinations. Dive depths range from 0-100 feet seawater fsw and dive durations may extend up to 6 h or more. Present decompression procedures mandate lengthy decompressions that in many cases impede mission accomplishment. This study explored the potential use of a hyperoxic helium-oxygen breathing mixture to reduce or eliminate in-water decompression time on these profiles. The protocol simulated operational diving conditions with respect to water temperature and exercise level. A total of 67 no-decompression dives were completed successfully using 40 O260 He as the breathing mixture 55 dives were 6 h in duration at depths ranging from 50 to 60 fsw, 6 dives were 8 h in duration at a depth of 60 fsw and 6 dives were 6.5 h in duration on a multi-level profile with depths ranging from 0-100 fsw. All dives used standard USN descent and ascent rates without decompression stops. One case of possible neurological Type II decompression sickness occurred during the series.