Decompression Theory

Part 1 - Explaining decompression theory

Decompression Theory

Decompression theory has a long and involved history. Some of the greatest scientific minds have been involved in the story of decompression. Despite 350 years of study there are still many aspects of and pioneers of deco. The story of decompression started in England in the seventeenth century and over the next 350 years the focus of our story jumps between England, the rest of Europe, as well as the United States and involved some of the most famous scientists of the ages.

Great scientific minds like Robert Boyle, John Dalton and Paul Bert all played an important part in putting in place some of the foundations of modern decompression theory.

crystaldive.com-koh-tao-diving-decompression-theoryRobert Boyle

The first of the great diving medicine innovators to describe decompression illness was Robert Boyle (1627-91), the Irish physicist and chemist who gave us the Boyle’s Law, so well-known to diving students all over the world.

In 1667, before diving was even known, Boyle had discovered decompression illness. Boyle was studying the behavior of gases and built a small pressure chamber, to see how animals reacted to different pressures.

He observed that a snake (a viper to be precise) became very distressed when the air removed from the ‘receiver’ in which it resided.

Boyle’s experimental notes record: “I observed the viper furiously tortured in our exhausted receiver, which had manifestly a conspicuous moving to and fro in the waterous humor of one of its eyes”.

This was the first recorded observation of the bubble formation that leads to decompression illness. Boyle recorded in his observations but had no idea as to why the bubble had been formed.

Rediscovery

Decompression illness was rediscovered in the early 19th century although at the time there was still no clear understanding of the cause of the disease. Workers involved in mining, tunnel construction or building work in pressurized underwater containers as well as the early hard hat divers began to notice a variety of symptoms when leaving the tunnel or the construction chamber or when ascending after a hard hat dive.

crystaldive.com-koh-tao-diving-decompression-chamberIn 1844 Royal Engineer Coronel Pasley (later Mayor General Sir William Pasley) was allocated the task of clearing the wreck oh HMS Royal George which had sunk in the Solent 1787 and was proving a hazard to navigation ships entering Portsmouth (UK), an important Naval harbor.

Pasley decided to use the opportunity to test and evaluate hard hat diving equipment.

During this same time diving bells were increasing in size. The industrial revolution produced high-capacity air pumps capable of sufficient pressure to keep water from entering these bells.

Diving bells then evolved into dry underwater chambers allowing several men to work in a dry environment.

In 1830 Lord Cochrane patented the use of compressed air to provide an air filled working environment underwater or in mines or tunnels which were below the level of groundwater.

This innovation greatly simplified the task of constructing bridge footings and tunnels. These dry, pressurized work areas were known as plenum pneumatic or Caissons, French for big box. This design was a major leap forward in engineering, as it allowed workers easy access from the surface and the pressure inside kept the worker area dry.

An air-lock was used to pass materials in and out or to change work shifts. The use of the Caisson grew rapidly as larger and more ambitious engineering works were undertaken. The men who worked in these big boxes became known as Caisson workers or just ‘Caisson’.

Caisson Disease

crystaldive.com-koh-tao-diving-decompression-caisson-diseaseAs the use of the caisson grew a large number of workers began to complain of symptoms similar to those encountered by the hard hat divers. Caisson workers reported a number of symptoms including dizzy spells, shortness of breath sharp acute pain in joins and abdomen.

After a period, the symptoms would reduce, but the worker was sometimes left with symptoms which refused to disappear completely. It was also noted that those who suffered the mysterious malady felt better when returned to the pressured environment of Caisson.

As projects got bigger and working pressures increased, the attacks to the mysterious malady increased, not only in number of victims, also in severity, so much so that fatalities started to occur frequently.

The term ‘malady du caisson’ or Caisson disease was first used in 1841 by a French mining engineer named Triger who noticed that coal miners working under increased atmospheric pressure suffered from muscular cramping and pains after returning to the surface.

Even Webster’s 1913 Dictionary the definition of Caisson’s Disease shows a clear explanation of the symptoms but no clear understanding of the cause.

Caisson’s disease continued to affect workers throughout the 1800s.

During the construction of the Brooklyn Bridge between 1870 and 1883 three people died and the 15% of those who suffered symptoms were left with some level of permanent paralysis.

Unfortunately, due to personality conflicts between James Eads and Washington Roebling, Eads never passed on the knowledge that had been gained during construction of the Saint Louis Bridge. Roebling took over from his father as a Chief Engineer on the Brooklyn bridge and was himself struck down with caisson’s disease in 1872 and remained painfully paralysed for the rest of his life.

crystaldive.com-koh-tao-diving-decompression-effects

It was during the construction of the Brooklyn Bridge that the term ‘bends’ was introduced for the first time. As the workers often had trouble standing straight their posture looked similar to the ‘Grecian band’ adopted by the fashionable women of the time, they began to call the problem ‘the bends’, a name still used today.

Author: Guillermo Sanchez (PADI IDCS #288160)

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