SUMMARY

This study describes the continuation of a previous survey into commercial air diving in the UK.

Logs of almost 130,000 dives from 1982 to 1988 inclusive were scrutinised. 126,980 of these dives were accepted into the survey. This included details of 333 incidents of decompression sickness (DCS).

Results confirmed the findings and conclusions of the original survey and supported the restrictions applied by the DSM 7/86 to surface decompression diving. The survey to 1988 further indicates that the limit line between "stressfull" and "non-stressful" dives proposed on the basis of the 1982/83 results (a D.P. Index of 30) was slightly too relaxed and that the limit based on PrT = 25 (D.P. Index approximately 20) would more accurately describe this division. In 1987, when the DSM 7/86 restrictions were relaxed, the DCS incidence rate remained unacceptably high and neurological decompression sickness continued to occur, indicating that the performance of the "improved" surface decompression tables was unsatisfactory. It is suggested that the enforcement of the DSM 7/86 would have prevented all Type 2 and the majority of Type 1 DCS episodes arising in 1987. The reimposition of these restrictions as DSM 5/88 was fully supported by the results for 1988, which showed a dramatic decrease in the DCS incidence rate in surface decompression diving. These restrictions on surface decompression diving in 1988, however, resulted in an increase in severity of dives carried out with in-water decompression, and a consequently marked increase in the DCS incidence rate in in-water-stop diving. Bell-TUP diving has been increasing over the past 3 years. These dives have been of greater than average severity, and episodes of DCS have occurred. The survey continues to monitor these phenomena.

INTRODUCTION

In response to concern expressed regarding Type 2 (neurological) decompression sickness (DCS2) by the AODC early in 1983, the Department of Energy commissioned a survey of commercial offshore air diving in the UK sector of the North Sea covering the period 1982/83. This survey was carried out by a retrospective analysis of individual dive logs and was reported in 1986. (Shields TG & Lee WB: "The Incidence of Decompression Sickness arising from Commercial Offshore Air Diving Operations In the UK Sector of the North Sea during 1982/83"; TG Shields, Advances in Underwater Technology, Ocean Science and Offshore Engineering, Vol 14, SUT 1988). The survey was limited in its scope, firstly by having to work with data of varying quality and reliability, but more importantly in that the industry's requirement that the individual diver would not be identifiable from the computer record meant that no analysis could be made of the individual's pattern of diving, and identification of possible contributory factors (for example, regular multiday dives) was not possible. The inability to approach the diver (for example, for information on his diving activity in areas other than the UK sector of the North Sea) meant that the potential effect of multiple episodes of DCS could not be assessed, nor could the contribution of the diver's state of fitness.

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