Twenty-First Century Surface-Supplied Heliox Decompression Table Development

The Surface-Supplied Helium-Oxygen (SS He-O2) Decompression Table in the current U.S. Navy Diving Manual (Revision 7, Change A) is an edited version of an original 1939 issue with a limited record of success in operational dives to depths of 240 feet sea water (fsw) or shallower. Recent theoretical evaluations indicate that schedules in this table for longer and deeper dives that are increasingly within the scope of desired U.S. Navy diving operations but have a limited history of use will incur unacceptably high risks of decompression sickness (DCS). Navy Experimental Diving Unit (NEDU) generated three tables of SS He-O2 decompression schedules to incur a 2.3 maximum estimated risk of DCS over operationally useful ranges of dive depth and bottom time and be considered as candidates to replace the current U.S. Navy SS He-O2 Decompression Table. One table was generated with a three-region unstirred tissue (3RUT) gas and bubble dynamics probabilistic model fitted to the he8n25 dataset used to produce the 1.3 atm oxygen partial pressure in helium tables in the current U.S. Navy Diving Manual. Numerical difficulties and inordinately long computation times required to solve the model equations for a given He-O2 dive thwarted more advanced applications of the 3RUT model to SS He-O2 diving. The two other tables were generated with an updated linear-exponential multi-gas (LEM) probabilistic model fit to a larger N2He_2016 dataset expanded to include more constant oxygen fraction He-O2 dives representative of SS He-O2 diving. The second of these tables included a modification to accommodate a 0.5 gas mixing error allowed in the U.S. Navy Diving Manual. After comparisons of the candidate SS He-O2 tables and the current MK 16 MOD 1 He-O2 decompression table, the latter table is recommended as the best candidate to replace the current U.S. Navy SS He-O2 decompression table.