Haldane's decompression model: Difference between revisions

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==Haldane's work==

[[File:Haldane inside the compression chamber.jpg|thumb|220px|right|Haldane inside his compression chamber]]

The [[British Admiralty|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 practice#Decompression tables|decompression tables]] for divers ascending from deep water.

In 1907 Haldane made a [[Diving chamber|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.

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:* As regards to carbon dioxide, the experiments of Haldane and Greenwood showed that partial pressure of CO₂ in the alveolar air remains constant with the rise of atmospheric pressure, hence, there can be no increase in CO₂ in blood during exposure to compressed air.

:* As regards to nitrogen, considerations should be taken for the saturation in body tissues.

* [[File:From Haldane's Book - Figure-1 N2 Saturation.jpg|thumb |The rate of saturation of any part of the body with nitrogen]] The rate of solubility of nitrogen per unit mass of tissue, varies greatly in different parts of the body, hence, after a sudden rise in air pressure, varies correspondingly.

* If the pressure is rapidly diminished to normal after exposure to saturation in compressed air, the venous blood will give off the whole of its excess of dissolved nitrogen during its passage to the lungs. If gas bubbles are formed in consequence of too rapid decompression, they will increase in size by diffusion into them, and thus cause blocking of small vessels. In order to avoid the risk of bubbles being formed during decompression, the decompression should be slow, and the rate of blood circulation can be increased considerably by muscular exertion.

* [[File:Haldane's Desat of N2 with different parts of the body with half-sat in 5-10-20-40-75 minutes.jpg|thumb |Decompression needs to be ''staged decompression'']][[File:Haldane's Desat of N2 different body tissues.jpg|thumb |Desaturation during ''uniform decompression'']] When a diver goes down for a very short time, the time occupied in the descent and ascent is taken into account. During descent, the diver is being saturated with nitrogen, so he should descent as rapidly as practical. During ascent on the other hand, Haldane showed that at the end of decompression there is a dangerous excess of saturation in all parts of the body except those which half-saturated in less than about seven or eight minutes. The goats used for stage decompression experiments were subjected to uniform decompression in same time and exposure, and within thirty-six decompression trials, one died, two were paralyzed, one had indefinite general symptoms of severe character, and eleven other cases of "bends" occurred beside two doubtful cases.

* Diving period:

:* For short diving periods of less than seven to eight minutes with no repetitive dive: Haldane's experiments on goats showed that sudden decompression in less than a minute after exposures up to four minutes at {{convert|75|psi|bar|abbr=on}}, equivalent to {{convert|42|m|ft}} of sea water, goats did not develop any symptoms, even when exposures were raised to six minutes in some cases. This coincides with reports at that time from the Mediterranean of skilled Greek divers, diving to {{convert|30|fathom|m}} who, should their gear become entangled on the bottom, will cut their air-pipe and line, and blow themselves up to the surface in less than a minute.{{Citation needed|date=May 2015}}

:* With dives exceeding a few minutes or brief repetitive dives: Hill and Greenwook compressed themselves to {{convert|91|psi|bar|abbr=on}}, equivalent to {{convert|53|m}} of sea water, a very high pressure and risky experiment, and had bends after decompression.{{Citation needed|date=May 2015}} [[File:From Haldane's Book - N2 Saturation for different body tissues.jpg|thumb |The saturation curves of Hill and Greenwook's experiment for parts of the body]]The saturation curves of their experiment for parts of the body were published.

[[File:Haldane - Bends of fore-leg in a goat.jpg|thumb|220px|right|One of Haldane's bent goats. Note the bend in the left foreleg.<ref name=haldane>{{Cite journal |date=June 1908 |journal=The Journal of Hygiene |volume=8 |pages=342–443 |number=3 |pmid=20474365 |pmc=2167126 |last1=Boycott |first1=A. E. |title=The Prevention of Compressed-air Illness |last2=Damant |first2=G. C. |last3=Haldane |first3=J. S. |url=http://archive.rubicon-foundation.org/7489 |doi=10.1017/S0022172400003399 |access-date=12 May 2015 |archive-url=https://web.archive.org/web/20110324171946/http://archive.rubicon-foundation.org/7489 |archive-date=24 March 2011 |url-status=dead }}</ref>]]

* Experiments continued on goats, and symptoms observed on goats were noted each time on appropriated schedule to record the presence of symptoms not the presence of bubbles:

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{{Reflist}}

{{Underwater diving|scidiv}}

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[[Category:Decompression theory]]