He-Nsub2-Osub2: Isobaric Shift and Saturation Decompression

A disabled submarine (DISSUB) crew exposed to increased atmospheric pressures resulting from flooding or other problems may incur a decompression obligation. They will then require not only gradual decompression to avoid decompression sickness (DCS), but decompression in specific gases due to operational limitations and to lower the risk for pulmonary oxygen toxicity. Nineteen dry chamber dives were conducted at the Naval Submarine Medical Research Laboratory (NSMRL) to explore the feasibility of an isobaric shift from air at five atmospheres (ATA) to Helium-Nitrogen-Oxygen (50% He40% N2-10% O2, TRIMIX) followed by decompression to the surface. These procedures parallel the potential operational scenario of returning the crew of a pressurized, disabled submarine (DISSUB) to the surface. Saturation dives were conducted by sequential experimental design, in which there was progressive shortening of the hold period following isobaric shift and/or shortening of decompression time. Initial pressurization was to 111 feet of seawater (fsw) (4.4 ATA) for 60 hours followed by compression to 132 fsw (5.0 ATA) on air for 12 hours, then the isobaric shift to TRIMIX was conducted. A hold of 24, 12, 8, or 4 hours at 132 fsw (5.0 ATA) was initiated, followed by a rapid upward excursion from 132 fsw 5.0 ATA) to 116 fsw and decompression to the surface with 57.5, 50.9, 44.5, or 41.2 hour schedules.