Manned Validation of U.S. Navy Diving Manual, Revision 7, VVAL-79 Air Decompression Schedules for Short Bottom Times in the 130-140 FSW Range

The U.S. Navy Diving Manual Air Decompression Table was promulgated in 2008, and a revised version calculated with the Wal-79 Thalmann Algorithm, was promulgated in 2016. The Swedish Armed Forces Diving and Naval Medicine Center (DNC) conducted a laboratory dive trial using the 2008 Air Decompression Table. Thirty-two dives to 132 fsw (40 msw) for 20-minute bottom time, using the 140 fsw / 20-minute schedule, resulted in two cases of decompression sickness (DCS). and median venous gas emboli (VGE) measurement at rest of KM grade Ill. These results motivated an examination of current U.S. Navy Air Decompression schedules. An air decompression schedule for exactly 132 fsw for 20-minute bottom time was computed with the Wal-79 Thalmann Algorithm and resulted in a 9-minute stop at 20 fsw. This schedule was tested in the Ocean Simulation Facility at the Navy Experimental Diving Unit. Divers dressed in swimsuit and t-shirt, immersed in 85 deg. F (29 deg. C) water, and breathing from surface supplied air, performed approximately 90 Watts cycle ergometer work while on the bottom and rested during decompression. Divers were monitored with 2-D echocardiography at 20-minute intervals for 2 hours post-dive. VGE at rest and with limb flexion were graded with an expanded EB scale. Dives were conducted in a group sequential trial designed to stop if DCS incidence exceeded 5 percent at 5 percent significance. Ninety-six man-dives were completed, resulting in no cases of DCS. The median (IQR) peak VGE grades were 3 (2-3) at rest and 3 (3-3) with movement. VGE grades remained elevated two hours post-dive with median grade 1 (1-3) at rest and 3 (1-3) with movement. Testing of a short, deep air decompression schedule computed with WAl-79 Thalmann Algorithm tested under diving conditions similar to earlier U.S. Navy dive trials resulted in low incidence of DCS.