Development of a Decompression Algorithm for Constant 0.7 ATA Oxygen Partial Pressure in Helium Diving.

Abstract : A total of 1582 man dives were done to test a computer algorithm used to compute decompression schedules for a closed circuit underwater breathing apparatus which maintains a constant 0.7 ATA PO2 in a helium diluent. The 47 test dives were all single depth dives up to 300 FSW deep with total dive times approaching 4 hours. The first three phases of testing resulted in a computer algorithm which appeared initially safe but which subsequently produced an unacceptably high incidence of decompression sickness (DCS) on a later dive series. Investigation of this high incidence of DCS on later dives lead to the identification of a workup phenomenon which showed that previous HeO2 diving will significantly reduce individual susceptibility to DCs. Further testing resulted in a computer algorithm which would compute safe decompression schedules for divers who are not worked up. The overall raw incidence of DCS for the entire dive series was 3.73% with 37% of all symptoms being Type 2. The overall incidence of DCS was 3% lower than that found during testing of a similar computer algorithm using a constant 0.7 ATA PO2 and a nitrogen diluent but the proportion of Type 2 DCS was higher using a helium diluent than when using a nitrogen diluent.