If the subject of this paper were simple and easy to resolve, it would not have been included in this proceedings. Increasing effective bottom working time, while keeping the decompression penalty as small as possible, is perhaps the central aim of all diving techniques. It is for this reason that the various diving techniques have been developed but only with saturation diving has the decompression penalty for unlimited working time been reduced to zero, at least until a series of working periods has been completed.
It would be useful at this stage to review the working times available using examples of different diving techniques, and the factors that act as constraints upon increasing working time and decreasing the decompression penalty (Table 1). Fundamentally, with all diving techniques, the limiting factor is the amount of inert gas taken up by the diver during the period under pressure and the time it takes during decompression for this to leave the diver. An allied limiting factor is that of oxygen toxicity. Pure oxygen cannot be used as a breathing mixture,(Table 1 is available in full paper) except in highly specialized military applications, because of its toxicity. This limits its use in replacing part of the inert gas of breathing mixtures in attempts to reduce inert gas uptake.
Considering scuba first, its use is limited to 165 feet in commercial diving because of the risk of nitrogen narcosis. In practice there are other potential problems with the technique such as in-water decompression stops, which make it less than ideal for routine use in the commercial diving industry. For example the maximum bottom time requiring no in-water stops for a 130 foot air dive is around 10 minutes, and for 165 feet it is around 5 minutes. Surface supplied air diving is, in effect, the diving industry's equivalent of scuba diving. Thus the constraints in use are similar, and there is the same depth limitation of 165 feet. Deeper than this a different breathing mixture must be used. The same limitation is imposed by nitrogen narcosis as during scuba diving, although the potential exists for an alternative heliox breathing mixture. This is generally not popular because of the extra cost and because in-water oxygen breathing is regarded as unsafe diving practice.
Moving to the next diving technique, that of bell bounce diving, there is little theoretical limitation to its use as the depth limitation imposed by nitrogen narcosis can readily be avoided by using a heliox breathing mixture. In practice, however, for dives of more than about 350 feet, with a bottom time of more than 60 minutes, most diving contractors would probably regard saturation as a more suitable technique because of the long decompression required for bell bounce diving.