Haldane's decompression model is a mathematical model for decompression to sea level atmospheric pressure of divers breathing compressed air at ambient pressure that was proposed in 1908 by the Scottish physiologist, John Scott Haldane (2 May 1860 – 14/15 March 1936), who was also famous for intrepid self-experimentation. Haldane prepared the first recognized decompression table for the British Admiralty in 1908 based on extensive experiments on goats and other animals using a clinical endpoint of symptomatic decompression sickness. The model, commented as "a lasting contribution to the diving world", was published in the Journal of Hygiene.
Haldane observed that goats, saturated to depths of 165 feet (50 m) of sea water, did not develop decompression sickness (DCS) if subsequent decompression was limited to half the ambient pressure. Haldane constructed schedules which limited the critical supersaturation ratio to "2", in five hypothetical body tissue compartments characterized by their halftime. Halftime is also termed Half-life when linked to exponential processes such as radioactive decay. Haldane's five compartments (halftimes: 5, 10, 20, 40, 75 minutes) were used in decompression calculations and staged decompression procedures for fifty years. Previous theories to Haldane worked on "uniform compression", as Paul Bert pointed in 1878 that very slow decompression could avoid the caisson disease, then Hermann von Schrötter proposed in 1895 the safe "uniform decompression" rate to be of "one atmosphere per 20 minutes". Haldane in 1907 worked on "staged decompression" – decompression using a specified relatively rapid ascent rate, interrupted by specified periods at constant depth – and proved it to be safer than "uniform decompression" at the rates then in use, and produced his decompression tables on that basis.
Previous work
Paul Bert Paul Bert (17 October 1833 – 11 November 1886) was a French physiologist who graduated at Paris as doctor of medicine in 1863, and doctor of science in 1866. He was appointed professor of physiology successively at Bordeaux (1866) and the Sorbonne (1869). Paul Bert was given the nickname of "Father of Aviation Medicine" after his work, La Pression barometrique (1878), a comprehensive investigation on the physiological effects of air-pressure, which pointed out that the symptoms of caisson disease could be avoided by means of very slow decompression. However, his work did not furnish data about safe decompression rates.
Schrötter Anton Hermann Victor Thomas Schrötter (5 August 1870 – 6 January 1928), an Austrian physiologist and physician who was a native of Vienna, was a pioneer of aviation and hyperbaric medicine, and made important contributions in the study of decompression sickness. He studied medicine and natural sciences at the Universities of Vienna and Strasbourg, earning his medical degree in 1894, and during the following year receiving his doctorate of philosophy. He was active in many fields of medicine and physiology. His first interest from 1895 was the investigation and combating of caisson disease, and during his tenure in Nussdorf he studied the numerous diseases that have occurred and was looking for ways of treatment and prevention. His published report in 1900 with Dr. Richard Heller and Dr. Wilhelm Mager, on air pressure disease is considered the basic German-language work of diving and hyperbaric medicine. Schrötter, Heller and Mager framed rules for safe decompression and believed that the decompression rate of one atmosphere (atm) per 20 minutes would be safe. Leonard Erskine Hill and Greenwood decompressed themselves without serious symptoms after exposure to 6 atm (610 kPa).
Haldane's work The Admiralty Committee needed to frame definite rules for safe decompression in the shortest possible time for deep diving, and hence, Haldane was commissioned in 1905 by the UK Royal Navy for this purpose, to design decompression tables for divers ascending from deep water. In 1907 Haldane made a decompression chamber to help make deep-sea divers safer and produced the first decompression tables after extensive experiments with animals. In 1908 Haldane published the first recognized decompression table for the British Admiralty. His tables remained in use by the Royal Navy till 1955. "The Prevention of Compressed Air Illness" was published in 1908 by Haldane, Boycott and Damant recommending staged decompression. These tables were accepted for use by the Royal Navy. Haldane introduced the concept of half-times to model the uptake and release of nitrogen into the blood in different body tissues, and suggested five body tissue compartments with half times of 5, 10, 20, 40 and 75 minutes. In his hypothesis, Haldane predicted that if the ascent rate does not allow the partial pressure of the inert gas (nitrogen) in each of the hypothetical tissues to exceed the environmental pressure by more than twice (2:1 ratio), then bubbles will not form in these tissues. Basically this meant that one could ascend from a depth of 30 metres (100 ft) – an ambient pressure of 4 bars (60 psi) – to 10 metres (33 ft) (2 bars (29 psi)) or from 10 metres (33 ft) (2 bars (30 psi)) to the surface (1 bar (15 psi)) when saturated, without a decompression problem. To ensure this, a number of decompression stops were incorporated into the ascent tables. The ascent rate and the fastest tissue in the model determine the time and depth of the first stop. Thereafter, the slower tissues determine when it is safe to ascend further.
Outline Haldane ran his experiments on some animals, illustrating the difference between different kinds of animals such as goats, guinea-pigs, mice, rats, hens and rabbits, but his main work and results were done on goats and men. Haldane stated in his paper: "In order to avoid the risk of bubbles being formed on decompression, it has hitherto been recommended that decompression should be slow and at as nearly a uniform rate throughout as possible. We must therefore carefully consider the process of desaturation of the body during slow and uniform decompression", hence the outline of his work is noted:
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