ABSTRACT
The most cost effective way to prepare for compressed air work at greater than 3 bars (gauge) pressure is to plan the decompression procedures to suit the operational situation rather than to attempt to fit a tunnelling operational or engineering plan to current diving tables. Special decompression procedures are needed when work is required at pressures greater than this. We have compared a variety of decompression approaches to this task using the DCAP Plus computer program; most of them take advantage of the benefits of oxygen for improved decompression, but also consider that the control of oxygen exposure is a major planning factor. Work in air with air decompression is inefficient, but is not limited by oxygen exposure. The most effective approach and one on which there is some experience is work in air with oxygen breathing during decompression. Even more effective decompressions are possible with oxygen-enriched air, but this becomes limiting due to oxygen exposure when used for the more stressful exposures, and requires breathing of prepared gas mixtures. For jobs requiring many man-days of work at high pressures the benefits of saturation techniques may offset the cost of the equipment. Saturation-excursion techniques can improve safety and make the final decompression shorter. An important aspect of using innovative decompression techniques is the requirement to validate their reliability; a new set of consensus guidelines makes it feasible to introduce into the workplace new techniques based on documented experience with little or no laboratory validation. It will be less efficient hence more expensive to work at higher pressures, but this can be done with no increase in risk, and for many situations will be the most cost effective approach.
