Tony L. Alleman and Joseph R. Serio*

Humans function well only within a narrow range of barometric pressures. Outside this range, they are subject to major physiologic stresses that occasionally result in disease. On land, workers are exposed to hyperbaric environments (i.e., increased barometric pressure) during tunneling projects that require the use of compressed air or when caissons are used to work in ground saturated with water. In addition, hyperbaric chamber support staff members are routinely exposed when they treat patients in hyperbaric medical treatment facilities. In the water, occupational exposures are diverse. Examples of exposures include breath-hold divers, such as the ama pearl divers of Japan, and compressed gas divers, ranging from instructors of recreational SCUBA students, who breathe compressed air, to saturation divers supporting offshore oil exploration, who dive in excess of up to 1000 ft of seawater (fsw), depending on the scope of the project, while breathing artificial gas mixtures. Divers can also be found inland. These divers are involved in such jobs as inspecting dams and reservoirs, cleaning filters, maintaining fish farms, placing underwater demolitions, and conducting police searches.

The first practical method developed for conducting useful work underwater was the diving bell, which is essentially an upside-down cone. Invented by Smeaton in 1778, the diving bell was the forerunner of the modern caisson ...

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