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NAUI Master Scuba Diver 152 Decompression and Recompression LEARNING GOALS In this chapter, you will: 1. Be introduced to the decompression and recompression terms presented in bold letters. 2. Learn about theoretical tissue, or compartment, halftimes. 3. Understand why NAUI uses the modified U.S. Navy Dive Tables. 4. Work with dive table calculation objectives listed in this section. 5. Learn the proper dive table procedures for: - Cold or strenuous dives - Ascent rate variations - Less than ten minute surface intervals - Multi-level diving - Omitted decompression - Flying after diving 6. Read the NAUI policy regarding mixed gas diving. 7. Learn two primary advantages of using a dive computer. 8. Learn several uses and names for hyperbaric chambers and state at least two hazards associated with chambers. 9. Learn about altitude diving and list at least four procedural differences between diving at altitude and diving at sea level. DECOMPRESSION THEORIES As you extend your diving range to new regions and countries, you may meet other divers using unfamiliar tables. Supporting each of these tables is a different decompression theory, each based upon research. Most of these theories, though not all, began with the work of Hill and Bert in 1870, and John Scott Haldane in England in 1908. The Haldane Theory Decompression sickness (DCS) is a serious bodily affliction caused by nitrogen bubble formation in the body, which is the result of too rapid a reduction of pressure. It is a problem which affects not only divers, but also construction workers in bridge piers and tunnels. These laborers typically work in pressurized chambers known as “caissons.” One type of decompression sickness was originally known as caissons disease, or a popularly used term “the bends,” as the limbs of those stricken distort with cramps and they walk with a stoop (when they can walk). At all times, the gases dissolved in the tissues in your body tend towards equilibrium with the surrounding gases. At the surface, your tissues are always at equilibrium, with as much gas going in as is going out, so the tissues have no net gain or loss of gas. When diving, much more gas enters the tissues than leaves, producing a net increase in the amount of gas in the tissues. This continues until the tissues are once again at equilibrium with their surroundings, or until you again change ambient pressure by changing depth or surfacing, whichever comes first. Haldane observed that animal subjects saturated at depths shallower than about 10 meters sea water (msw) 33 fsw, or 2 ata, could be brought directly to the surface without showing signs of “the bends.” This observation implied that tissues of animals, including humans, at equilibrium at 10 msw (33 fsw) could be surfaced without incident. Surfacing from 10 msw (33 fsw) is a total pressure reduction of 50%. Extrapolating from this information, it was reasoned that tissues could always withstand a total pressure reduction of 50%, whether from 10 msw (33 fsw) to the surface or from 30 m 99 ft (4 ata) to 10 m 33 ft (2 ata). This is the well-known “Haldane Ratio” principle of 2:1 pressure reduction (figure 5-1). Later research proved that this ratio was too liberal and has since been modified to approximate 1.58:1. The human body is not made up of just one type of tissue, however. The heart, brain, muscles, bones, blood, 33 feet (10 m) = 66 fswa (20 mswa) FIGURE 5-1. SUMMARY OF HALDANE’S RATIO =2:1 99 feet (30 m) = 132 fswa (40 mswa)


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