Summary

Since the majority of diving tasks from a drilling rig can be accomplished within 30 minutes total bottom time, it is possible, with good operational planning and experienced divers, to effectively use bounce diving techniques to about 600 feet. Tasks requiring longer bottom times can be accomplished with "back to back" diving techniques using a second deck decompression chamber and additional divers. Saturation can be used effectively from 300 feet, but would probably only be justified if unusually long bottom times were required. Such capability is more applicable to construction work rather than drilling. Below 600 feet, bottom times must be limited to avoid prohibitively long decompression times.

Control of compression rates will also use up available bottom time so that the effective working time is reduced to an impracti-cally short period. The absolute limit for bounce diving is not easy to define, but for all practical purposes it is likely to be around 750 feet. The wise operator will provide for full saturation capability once he gets into water depths over 600 feet. The decision to utilize saturation techniques in this range will depend largely on the capability of the diving crew to accomplish the work within the time limits allowed, so they get through both the compression and decompression "windows" required for a bounce dive,

A ten minute job at 650 feet, if not completed in time, can force the crew to saturate in order to complete the work, thus tying up the decompression facilities for a six or seven day period. On the other hand, one might deliberately saturate the crew if the job is the first of an anticipated series of tasks (such as might occur if the marine riser is dropped and the BOP stack damaged). The divers would then be retained in saturation at a suitable storage depth, which would enable them to make rapid excursions to bottom pressures for extended working periods.

Once a depth of about 600 feet is reached, there is no present alternative to saturation. The use of sophisticated saturation diving equipment and highly qualified experienced personnel is mandatory.

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