NAUI Master Scuba Diver 164 Decompression and Recompression General Characteristics of Hyperbaric Chambers Hyperbaric chambers are pressure vessels (figure 5-17). They contain a volume of gas which can be held at a pressure different from the ambient pressure surrounding them. Chambers are usually cylindrical in shape with hemispherical ends. Some chambers used in commercial diving are completely spherical. These shapes allow hull strength to be achieved via efficient use of structural material. Certain characteristics are used for describing chambers. To relate and compare one chamber to another, diameter measurements are commonly used. The 137 cm (54 in) diameter chamber is often found in diving communities. It is a relatively small, economical chamber capable of treating persons with an inside tender and switching personnel during the treatment, if necessary. The 244 cm (96 in) chamber may be found in large medical facilities where its large size allows many medical patients to be treated simultaneously. On the other hand, a 66 cm (26 in) chamber may also be found in medical facilities where its small size allows one medical patient to be treated in a cost effective manner. In addition to using diameter denotations, chambers are also described by their rated working pressure, which is usually expressed in pounds per square inch (psi) or atmospheres absolute (ata). Most chambers for treating divers are rated to six ata working pressure, or 50 msw (165 fsw). Many chambers used for medical treatment are rated for three ata, or 20 msw (66 fsw). They can be very useful for more common decompression sickness treatment. Most of the treatment for DCS and AGE is conducted at 18 msw (60 fsw). Chambers can also be characterized by the number of compartments and “locks” they have. Locks are doorways or access openings which are pressure sealed when closed. Compartments are spaces which can be pressurized independent of each other and of ambient pressure. Compartments are separate enclosures sharing a common lock between them and are properly called “chambers” or “locks.” A chamber with two compartments might therefore be called a multi or double-lock chamber with inner and outer doors and inner and outer chambers. If capable of containing more than one FIGURE 5-17. HYPERBARIC CHAMBER PHOTO COURTESY OF SUBMARINE MANUFACTURING & PRODUCTS LTD. individual in the inner chamber, it could also be termed a multiplace, multilock chamber. Some chambers have small compartments for passing supplies in and out. These compartments are termed “medical locks.” The doors (locks) on medical locks commonly open outward and must therefore be “dogged” closed to be sealed against the internal pressure. The doors (locks) of the large occupancy chambers commonly open inward so that increased internal pressure works to seal the door closed. Any given chamber will have a number of “penetrators” or sealed holes through which various tubes or wires penetrate into the inside space. During chamber design and fabrication, penetrators will be incorporated to meet the needs of the chamber’s anticipated uses. To increase and decrease the pressure within the chamber, penetrators with valve systems input gas supplies and similar valved pipes are used to exhaust gases from the chamber. These pipes constitute the plumbing of the chamber. Communications are established between the inside and outside of the chamber by wires introduced through a penetrator. Lighting and electrical cables may also penetrate the chamber hull. Monitoring devices may penetrate the hull to sense internal atmospheric conditions or to detect occupant status changes. Medical patients in small chambers may need drugs and fluids or breathing assistance provided to them via special penetrators specifically designed for these purposes.
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