Decompression theory

Not to be confused with Decompression practice or Decompression sickness.
Scuba diver decompressing at a planned stop during ascent from a dive

Decompression theory is the study and modelling of the transfer of the inert gas component of breathing gases from the gas in the lungs to the tissues and back during exposure to variations in ambient pressure. In the case of underwater diving and compressed air work, this mostly involves ambient pressures greater than the local surface pressure,[1] but astronauts, high altitude mountaineers, and travellers in aircraft which are not pressurised to sea level pressure,[2][3] are generally exposed to ambient pressures less than standard sea level atmospheric pressure. In all cases, the symptoms caused by decompression occur during or within a relatively short period of hours, or occasionally days, after a significant pressure reduction.[4]

The term "decompression" derives from the reduction in ambient pressure experienced by the organism and refers to both the reduction in pressure and the process of allowing dissolved inert gases to be eliminated from the tissues during and after this reduction in pressure. The uptake of gas by the tissues is in the dissolved state, and elimination also requires the gas to be dissolved, however a sufficient reduction in ambient pressure may cause bubble formation in the tissues, which can lead to tissue damage and the symptoms known as decompression sickness, and also delays the elimination of the gas.[1]

Decompression modeling attempts to explain and predict the mechanism of gas elimination and bubble formation within the organism during and after changes in ambient pressure,[5] and provides mathematical models which attempt to predict acceptably low risk and reasonably practicable procedures for decompression in the field.[6] Both deterministic and probabilistic models have been used, and are still in use.

Efficient decompression requires the diver to ascend fast enough to establish as high a decompression gradient, in as many tissues, as safely possible, without provoking the development of symptomatic bubbles. This is facilitated by the highest acceptably safe oxygen partial pressure in the breathing gas, and avoiding gas changes that could cause counterdiffusion bubble formation or growth. The development of schedules that are both safe and efficient has been complicated by the large number of variables and uncertainties, including personal variation in response under varying environmental conditions and workload.

  1. ^ a b Cite error: The named reference USNDM R6 3-9.3 was invoked but never defined (see the help page).
  2. ^ Cite error: The named reference Van Liew and Conkin 2007 was invoked but never defined (see the help page).
  3. ^ Cite error: The named reference FAA was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference USNDM R6 20-3.1 was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference Gorman was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference Wienke was invoked but never defined (see the help page).