Decompression tables

Tables have been produced for several modes of decompression, including surface oriented in-water and surface decompression profiles for air and mixed gases, with and without oxygen accelerated decompression, for constant oxygen fraction diving and for constant oxygen partial pressure diving, for repetitive dives, and for saturation diving. No-stop tables are also available for repetitive dives. Tables for nitrox diving with a single mixture and for altitude diving may be published as separate tables or as equivalent depths to be used with standard sea level air tables. == Examples of decompression tables and procedures==

1% Risk tables 1% Risk tables are tables which satisfy the condition of a high probability (c0.95) of a low risk (c0.01) of producing symptomatic decompression sickness if followed according to the instructions. The condition may be stipulated for the no-stop limit, or may include profiles requiring staged decompression. Similar tables for other risk conditions like 5% risk tables have also been produced. Statistical analysis of a large number of actual relevant exposures is necessary for reliable results, and these may only be available for a subset of the desired range. US Navy Decompression Tables Several iterations of US Navy air, nitrox and heliox decpmpression tables have been published, for both constant gas fraction (open circuit) and constant oxygen partial pressure (closed circuit). The US Navy has used several decompression models from which their published decompression tables and authorized diving computer algorithms have been derived. The original C&R tables used a classic multiple independent parallel compartment model based on the work of John Scott Haldane in England in the early 20th century, using a critical ratio exponential ingassing and outgassing model. US Navy heliox tables US Navy saturation tables The first version of the US Navy saturation decompression procedures was published in the US Navy Diving Manual Revision 2 in 1976. They allowed decompression to start with an ascending excursion, and used a constant slow rate of decompression until 60 msw, after which varying rates were used to the surface. Chamber oxygen partial pressure of 350 to 400 mbar was used until the fire risk zone, after which the oxygen fraction was limited to between 19% and 23% for the final ascent. Decompression was suspended for a night rest stop from midnight to 06:00 and an afternoon stop from 14:00 to 16:00, leaving up to 16 hours per day for decompression. US Navy Diving Manual Revision 7 of 2016 left the rates of decompression unchanged, but the oxygen partial pressure of the chamber atmosphere was increased to 440 to 480 mbar, and the timing of rest stops could be shifted to suit operational requirements. ==Comparison of schedules==

Two criteria have been used in comparing decompression tables: Safety and efficiency, where decompression efficiency is defined as the ability of a schedule to provide safety from decompression sickness in the shortest time spent decompressing, and decompression safety is measured by the probability of decompression sickness incurred by following a given schedule for a given dive profile. The large variations in human response to decompression profiles makes a 0% incidence of decompression sickness not realistically practicable. However, a decompression sickness incidence of 1% or less is possible, and may be considered sufficiently safe. When comparing two schedules of equivalent safety, the one which requires less decompression time is regarded as more efficient. The traditional method of comparison uses symptomatic DCS as the criterion, but ultrasonic bubble counts have become a useful tool for comparison. To illustrate the range of conclusions that the different models can come to, some figures are quoted from Huggins' 1992 "Dynamics of Decompression Workshop" document for no stop limits for a square profile dive to 100 fsw: • US Navy air tables (1965) 25 minutes • NAUI 22 minutes • PADI, BSAC, Jeppesen, Huggins 20 minutes • German Tables 18 minutes • DCIEM Tables 17 minutes • Maximum Likelihood 1% Risk Tables 8 minutes ==Alternatives to decompression tables==

Dive computers A dive computer, personal decompression computer or decompression meter is a device used by an underwater diver to measure the elapsed time and depth during a dive and use this data to calculate and display an ascent profile which, according to the programmed decompression algorithm, will give a low risk of decompression sickness. Decompression software is generally used to produce a set of tables for a specified dive profile when the dive can be realistically planned to follow the profile, and usually a few contingency schedules to allow for plausible deviations from the plan. ==See also==