Theoretical Heat Losses and Survival Times in Cold Hyperbaric Helium Environments

Although the optimum temperatures for divers in He-O2environments as a function of depth (pressure) has been established, survival times at nonoptimum temperatures has not been quantitatively determined. In an attempt to do so, the theoretical rates of heat loss, and estimated survival times, were calculated for temperatures of 35,45,55,65 and 75 deg. F at pressures of 400,600,800, and 1,000 fsw (feet of seawater). This was done both for unprotected divers and those with thermal protection sufficient to reduce radiative and convective heat losses by 75%. As the major contributing factor was respiratory heat loss, effective insultation by way of protective garments does not contribute significantly to survival time, especially at the higher pressures and colder temperatures. For the pressures and temperatures considered, survival times ranged from several hours to less than 10 minutes. This can have serious implications in the case of an emergency rig abandonment while divers are at pressure; where they would be set adrift in a pressurized unheated bell.