These models, such as the Bühlmann decompression algorithm, are modified to fit empirical data and provide a decompression schedule for a given depth and dive duration using a specified breathing gas mixture.Since divers on the surface after a dive may still have excess inert gas in their bodies, decompression from any subsequent dive before this excess is eliminated needs to modify the schedule to take account of the residual gas load from the previous dive. This will result in a shorter allowable time under water without obligatory decompression stops, or an increased decompression time during the subsequent dive. The total elimination of excess gas may take many hours, and tables will indicate the time at normal pressures that is required, which may be up to 18 hours.Decompression time can be significantly shortened by breathing mixtures containing much less inert gas during the decompression phase of the dive (or pure oxygen at stops in 6 metres (20 ft) of water or less). The reason is that the inert gas outgases at a rate proportional to the difference between the partial pressure of inert gas in the divers body and its partial pressure in the breathing gas; whereas the likelihood of bubble formation depends on the difference between the inert gas partial pressure in the divers body and the ambient pressure.
During the EVA they breathe 100% oxygen in their spacesuits, which operate at 4.3 psi (0.30 bar), although research has examined the possibility of using 100% O2 at 9.5 psi (0.66 bar) in the suits to lessen the pressure reduction, and hence the risk of DCS. Treatment
Recompression on air was shown to be an effective treatment for minor DCS symptoms by Keays in 1909. Evidence of the effectiveness of recompression therapy utilizing oxygen was first shown by Yarbrough and Behnke, and has since become the standard of care for treatment of DCS. Recompression is normally carried out in a recompression chamber. At a dive site, a riskier alternative is in-water recompression.Oxygen first aid has been used as an emergency treatment for diving injuries for years. Particularly if given within the first four hours of surfacing, it increases the success of recompression therapy as well as decreasing the number of recompression treatments required. Most fully closed-circuit diving rebreathers can deliver sustained high concentrations of oxygen-rich breathing gas and could be used as a means of supplying oxygen if dedicated equipment is not available.It is beneficial to give fluids, as this helps reduce dehydration. It is no longer recommended to administer aspirin, unless advised to do so by medical personnel, as analgesics may mask symptoms. People should be made comfortable and placed in the supine position (horizontal), or the recovery position if vomiting occurs.