Thermodynamic approach to decompression.

[Gene_Hobbs]

One of the most often quoted papers in discussions of 'deep stops' and the 'oxygen window' is the 1965 LeMessurier and Hills paper describing their findings from the Torres Strait diving techniques (1). Hills later went on to describe this work in MUCH greater detail as a part of his thesis in 1966 (2). Both of these reports have been difficult to locate for many divers and we continually receive requests for assistance in locating them. Today we added a paper by Hills that describes much of his work in great detail (3). Below is the summary of that article written for SPUMS by Dr. Hills.

I hope this stimulates some good thoughts and consideration for the upcoming Deep Stops Workshop in Salt Lake City.

1. LeMessurier and Hills. (1965) Decompression Sickness. A thermodynamic approach arising from a study on Torres Strait diving techniques. Hvalradets Skrifter, Nr. 48, 54-84.
2. Hills. (1966) A thermodynamic and kinetic approach to decompression sickness. Thesis
3. Hills. (1978) A fundamental approach to the prevention of decompression sickness. South Pacific Underwater Medicine Society Journal 8(2): 20-47. RRR ID: 6176

SUMMARY - This article presents a hard look at the fundamental issues underlying the formulation of preventive decompression. The author’s interest in this subject was captivated some fifteen years ago when taking instrument recordings of the remarkable decompressions routinely followed by pearl divers - particularly the Okinawans operating in the Torres Strait and elsewhere along the northern coast of Australia. This study revealed a very efficient decompression practice derived purely by trial and error at the expense of maybe several thousand lives and serious injuries. These remarkable practices were derived over half a century when that area supplied the world with the pearl shell which was in great demand before buttons were made of plastic. Working at Adelaide University the author and his aeromedical colleagues were just in time to put on record these practices before the pearling industry dwindled to a state at which that vast wealth of invaluable human experience would have been lost for ever.

The methods employed by those divers were both successful and much more economical on time than Naval practice. Moreover their emphasis upon spending much more time deeper at the start of decompression and surfacing directly from 25-35 feet was totally incompatible with the Haldane rationale and neo-Haldanian calculation methods for diving table formulation at the peak of popularity at that time. This discovery stimulated much scientific work at Adelaide, leading to concept of an equilibrium state rather than a supersaturated state as the most relevant in determining the imminence of bends. Publication of this approach in 1966 presented the first comprehensive challenge to the Haldane method of formulating decompression tables as elaborated by the US Navy in particular. The major point of divergence was to point out that only equations were used to formulate tables and that, whatever the accompanying words, conventional equations assumed that the bends-free dive was bubble-free, pointing out why the diver was so disadvantaged if this proved to be incorrect.

There is now much more scientific evidence to support the Thermodynamic Approach which has been updated recently in a book entitled “Decompression Sickness: The Biophysical Basis of Prevention and Treatment” (published by John Wiley’s in New York and London). This paper is a distillate of that work. In order to avoid distraction from the main theme, some statements are made with minimal supporting data, if any, but the relevant references and detailed explanation can all be found in the book.

________________________
We work hard to make sure this type of information is made available to the public. PLEASE consider a donation to our '$5k for 5k' fundraiser. Thanks for your support!

________________________