<P> Astronauts aboard the International Space Station preparing for extra-vehicular activity (EVA) "camp out" at low atmospheric pressure, 10.2 psi (0.70 bar), spending eight sleeping hours in the Quest airlock chamber before their spacewalk . 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% O at 9.5 psi (0.66 bar) in the suits to lessen the pressure reduction, and hence the risk of DCS . </P> <P> All cases of decompression sickness should be treated initially with 100% oxygen until hyperbaric oxygen therapy (100% oxygen delivered in a high - pressure chamber) can be provided . Mild cases of the "bends" and some skin symptoms may disappear during descent from high altitude; however, it is recommended that these cases still be evaluated . Neurological symptoms, pulmonary symptoms, and mottled or marbled skin lesions should be treated with hyperbaric oxygen therapy if seen within 10 to 14 days of development . </P> <P> 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 . </P> <P> Oxygen first aid has been used as an emergency treatment for diving injuries for years . 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 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 . </P>

How far down before you get the bends