Chapter 5- Decompression and Recompression Decompression and Recompression 157 can be produced which are usable at reduced atmospheric pressures. Canadian Theory In contrast to the theories already mentioned, the Canadian tables published by the Defence and Civil Institute of Environmental Medicine (DCIEM) are not derived from the work of Haldane. None of these theories is an exact representation of the physics and physiology of the human body in decompression, but rather a fitting of mathematical equations to a time-depth history and a symptom-free result. Haldanian equations utilize parallel tissues, each taking up and giving off gas from the ambient environment without regard to neighboring tissues. The DCIEM theory employs a set of serial tissues, the first of which takes up and gives off gas from the environment. The second and succeeding tissues take up and give off gas from the preceding tissue only, not from the ambient gas supply. This serial model has been designed to produce results which are conservative compared to the U.S. Navy tables. Tables produced from this theory, applicable to sport diving situations, were validated using Doppler measurements to detect sub-clinical decompression stress or “silent bubbles.” The resulting tables should provide the best margin of safety based on human experiment. DIVE TABLES Of the numerous dive tables available throughout the world today, NAUI recommends the use of the U.S. Navybased dive tables as modified for recreational diving by NAUI’s reduced time limits. More information and data are available for the Navy tables than for any other tables in existence. It is strongly recommended, however, that limits less than the Navy no-decompression limits be considered when using the U.S. Navy tables and that a stop in the 3-6 m (10-20 ft) zone for three to five minutes be performed at the end of every dive greater than 18 m (60 ft) in depth. The stop time does not count as either dive time or surface interval time. For the purposes of discussion within this text, the no-stop limit for a given depth will be the limits identified on the NAUI Dive Tables. For example, your no-decompression limit for 18 m (60 ft) is 55 minutes (Group “I”) rather than 60 minutes (Group “J”). The Bottom Time (Minutes) 20 40 60 80 100 120 140 USN NDL Depth 12m 40' 18m 60' 24m 80' 30m 100' 36m 120' 42m 140' 48m 160' 54m 180' 60m 200' FIGURE 5-8. U.S. NAVY NO-DECOMPRESSION LIMITS
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