Health outcome following multi-day occupational air diving.

Acclimatization to decompression stress has been reported in caisson workers and helium-oxygen divers; however the alternative notion that the risk of decompression sickness increases with successive days of diving is widespread. We examined 201 multi-day series of 2 to 29 diving days identified retrospectively in a database of occupational air dives for evidence of acclimatization or sensitization. Decompression related health status was measured using a self-administered diver health survey; resulting scores were analyzed by linear modelling. Daily diving consisted of 1-3 dives each to mean maximum depth of 17.2 (SD 3.9) meters seawater for a mean duration of 23 (SD 17) min. Daily diver health scores increased with calculated daily risk of decompression sickness but were not influenced by the order of dives in multi-day series. Poor health outcome indicated by treated decompression sickness and diver health scores > 8 occurred early in multi-day series. There was no evidence of sensitization to decompression stress whereas the timing of poor health outcomes suggests an element of acclimatization.