[Iris7]

The capsule was designed for a helium-oxygen-CO2 atmosphere. No nitrogen was in the mix in the attempt to control bends in case of sudden depressurization. The helium concentration after launch was lowered until the cabin pressure was 3 pounds per square inch of pure oxygen plus CO2 enough for metabolic needs. The reason was bends, reduction in weight, seemed like a good idea.

The electrical insulation, seat padding, paint, spacesuits, all the possibly flammable stuff was made of Nomex, pvc, and similar stuff TOTALLY FIREPROOF in the designed atmosphere.

An unnamed big shot decided that the thing to do was change to pure oxygen-CO2 mix, even on the pad, where the pressure in the capsule had to be 15 pounds per square inch so that the capsule would not be crushed by atmospheric pressure. Pleas by technical people that all that stuff not flammable in a 3 pound per square inch oxygen atmosphere would burn like a roman candle, like a cutting torch, in pure oxygen at 15 pounds per square inch. Well, the Big Boy would not back down. Maybe it was a spark caused the fire in the capsule, sitting on the ground, 15 pounds per square inch of pure oxygen atmosphere inside.

[snippy_about_it]

An unnamed big shot...

Isn't that always the way it is. A good leader listens. A bad one just enjoys his position of power.

Thanks for the explanation of the atmosphere mixture.

[SAMWolf]

An unnamed big shot decided that the thing to do was change to pure oxygen-CO2 mix... Pleas by technical people that all that stuff not flammable in a 3 pound per square inch oxygen atmosphere would burn like a roman candle, like a cutting torch, in pure oxygen at 15 pounds per square inch.

Bureacrats!!