ABSTRACT

A computer data bank set up by Comex to process diving reports has been used to control and improve diving procedures. Analysis of 5744 early saturation dives proved the existence of an optimum ascent rate for saturation decompressions with a 600 mbar chamber P02. New saturation decompression procedures were developed and validated using the data bank.

INTRODUCTION

As a commercial diving company, Comex continually faces the problem of controlling and developing its diving procedures. However, it must be admitted that after almost 100 years of diving and research the mechanisms of decompression are still not completely understood and that the development of decompression procedures remains largely a matter of trial and error. For this reason, Comex studied the possibilities of using a diving report system for the monitoring of its operations.

The diving reports are working documents which allow operational personnel to runs specific check-list, go through pre-defined schedules and keep records of relevant parameters. These reports contain invaluable information concerning the operations, but a major difficulty remains of how best to process this mass of data to benefit from the offshore experience. In 1974 Comex started a computer system to process its diving reports and try to access this information efficiently. The system has been kept running ever since and now contains over 150,000 diving reports collected from worldwide operations. The files contain data on all diving methods (air, mixed gas diving or deep diving), all types of work (construction, hyperbaric welding, inspection, maintenance,...) and constitute a unique source of information on commercial diving.

The Comex Deta Bank has been used to study diving activity, analyse market trends and manage personnel, but its most notable application has been in the monitoring of diving procedures. statistical analysis of the diving reports has been turned into a scientific method for decompression procedure development that was used for the revision of the French Air decompression tables in 1986 (1). The purpose of this paper is to illustrate how this method was used to develop and validate new Comex Heliox Saturation Procedures in 1984. The previous Comex saturation procedures specified constant chamber Oxygen partial pressure (PO2) combined with varying rates of ascent, according to the theories in force at the time. The introduction of the "critical volume" assumption (2) and the work of VANN (3) indicated that there should be a linear relationship between the safe rate of saturation decompression and chamber PO2. Accordingly, a decompression with a constant chamber PO2 should be conducted with a constant rate of ascent.

Because the outcome of a decompression is unpredictable and depends on a large number of factors such as dive conditions or individual susceptibility (4), the study of decompression safety performances thus requires recording thousands of dives carried out by hundreds of different divers. Only commercial offshore operations can provide the large volume of information necessary for a meaningful statistical analysis. The objective was to determine whether or not Comex Data Bank would support the emerging theories and whether better procedures could be designed.

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