A New Dynamical Theory of Decompression

Abstract

We present a new way of taking in account the dynamics of the gas phase during decompression. This preliminary study, although being potentially capable of dealing with extreme dives, far from the no-stop limit, is not developed as a practical tool yet. It is based on the analysis of certain hypotheses underlying classical models using Maximal Values (M-Values). We derive a reduced set of ordinary differential equations, depending only on three empirical parameters. After having explained how the theory is built, we propose some values of the parameters that match the known surface M-Values well. Then we examine, for a single compartment, the theoretical predictions in the case of an abnormal situation (missing decompression stops) and in the case of dives with mixes containing helium (trimix and heliox). The results are more realistic than those of neo-Haldanian models. This new theory is capable of explaining why decompression accidents cannot occur immediately and why they can be delayed. The efficiency of oxygen breathing in such a situation is also well explained. More generally, the tolerance to inert gases depends on the breathed mix. In the present state, this theory, which is different from the Reduced Gradient Bubble Model (RGBM) and Variable Permeability Model (VPM), has an explanatory power that goes beyond the simple computation of decompression stops. Once developed as a full model, validated and definitively tuned, it could lead to a probabilistic approach of the safety, which is required by the extreme dives performed when exploring certain syphons.