1989-07-01

Decompression Sickness Risks for European EVA 891546

The design of a European space suit with a design pressure of 500 hPa requires a re-evaluation of the protective procedures -for space suit decompression. By analysis of the relevant literature, published decompression data from altitude chamber exposures, nitrogen/oxygen (nitron) saturation dives, and various decompression tables, an R factor of 1.2 and a tissue half-time (t1/2) of 360 minutes in a single-tissue model have been identified as appropriate operational values. On the basis of an acceptable risk level of approximately IX, oxygen prebreathing times are proposed for (a) direct pressure reduction froo 1013 hPa to a suit pressure of 500 hPa, and (b) staged decompression using a 700 hPa intermediate stage in the spacecraft cabin. In addition, factors which influence individual susceptibility to DCS are identified. First evidence is found for body fat, body weight and age. The effects of previous DCS, sex, patent formen ovale and blood complement sensitivity still need confirmation. To minimize the risk during actual EVA, astronauts should be monitored for venous gas bubbles by the Dappler ultrasonic method. Finally, treatment procedures, including emergency (“first aid”) procedures which involve a hyperbaric capability of the space suit on board the spacecraft, are proposed.

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