Exploration missions are expected to use variable pressure extravehicular activity ( EVA ) spacesuits as well as a spacecraft " exploration atmosphere " of 56.5 kPa ( 8.2 psia ) , 34 % O2 , both of which provide the possibility of reducing the oxygen prebreathe times necessary to reduce decompression sickness ( DCS ) risk . Previous modeling work predicted 8.4 % DCS risk for an EVA beginning at the exploration atmosphere , followed by 15 minutes of in - suit O2 prebreathe , and 6 hours of EVA at 29.6 kPa ( 4.3 psia ) . In this study we model notional prebreathe protocols for a variable pressure suit where the exploration atmosphere is unavailable .