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Chapter 5- Decompression and Recompression Decompression and Recompression 165 Compressors and Gas Sources To pressurize chambers, compressors or sources of already compressed gas are needed. Backup systems, either compressors or gas cylinders, must also be present in case of primary source failure. Pressures required for chambers are relatively low but the volumes of gas involved are usually quite high. A typical 137 cm (54 in) chamber’s inner lock is some 2.4 m (8 ft) long (the chamber is about 3.6 m (12 ft) long overall) and has a volume of approximately 3,429 l (120 cubic feet). High volume low pressure air compressors are less expensive than high pressure compressors and are commonly used for chambers unless a high pressure compressor is already present for other reasons. Just as with compressors for scuba cylinders, chamber compressors must use special lubricating oils and air intakes must be guaranteed clean pure air. Proper maintenance is very important. Cylinder banks of compressed air can be used as backup gas sources for chambers as well as scuba cylinder fill stations. Cylinder banks of compressed oxygen are used as sources of oxygen breathing gas in larger air pressurized chambers. Liquid oxygen sources are commonly used to supply oxygen gas for hospitals and are the primary oxygen source for many hyperbaric chambers. Gases such as nitrogen, helium, nitrogen-oxygen, or helium-oxygen mixtures find special application in the commercial diving industry. These special gases are usually stored in compressed gas cylinders and may be available for chamber use if needed. Chamber Types and Their Uses A variety of chambers are available. Purchase or installation choices are made on the basis of intended use and cost-effectiveness. In hyperbaric medical facilities, the number of patients that must be treated at one time usually determines the size of the chamber. For the recreational diving community, pressure needs, size (room for inside tender and patient), and simplicity (i.e., getting the job done at minimal cost) are determining factors in chamber size. Owing to infrequent use and little or no monetary reimbursement for treatments, chambers solely dedicated to treating recreational divers usually lose money or break even at best, even with volunteer help or local government support. Ideally, the recreational diver would be treated at a large medical or commercial facility if one is close by. However, the unpredictability and long treatment schedules for the injured diver can wreak havoc with routine scheduled operations. The news that a recreational diver is “bent” is not a welcome for anyone, including the diver. If the diver presents himself for treatment as soon as even suspicious symptoms occur, the outcome is usually good, however. Treatment personnel receive a lot of gratification from knowing they have returned an individual to a happy, productive life. Prompt treatment is directly related to the efficiency in attaining lasting resolution. Unfortunately, this is not always the outcome. Divers should know what type of recompression facility is available to them in their diving area, how to contact the facility for consultation, and how to quickly get there for treatment. It is usually required that a diver be referred by a hospital or physician for treatment in a chamber, if there is none at the chamber. Monoplace Single Lock Small, acrylic plastic, one-person, one-lock chambers are at some medical centers. Their normal use is for hyperbaric medical therapy of various conditions, such as gas gangrene. They use a 100% oxygen environment pressured to less than 3 ata. These chambers can treat less severe cases of decompression sickness. They are not preferred for life-threatening decompression sickness or air embolism cases because of pressure limitations (see previous section). They are often used for follow-up treatment of decompression sickness in a mode similar to their use in medical therapy. Small steel chambers rated at higher pressures (i.e., 6 ata or higher) have been used to transport victims under pressure using a total air environment. To be useful, they must be capable of “mating” with the treatment facility’s lock so that the victim can be transferred under pressure into the treatment chamber. Conceptually, such chambers are a holding vessel used to inhibit deterioration of the victim prior to reaching a treatment facility. However, once locked into such a chamber, victims cannot receive hands


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