It wasn’t that the American engineers and designers were unaware of the fire hazard. If weight had not been such a crucial issue when designing the Mercury capsule, they would not have gone withb pure oxygen design. As I mentioned aerlier, the original Apollo Command Module was being designed even before Mercury had flown, so pure oxygen was retained as a basic requirement for Apollo as well- again to save weight.

By 1967, the technicians had become so used to dealing with pure oxygen that they had grown casual and blase about the risk and minimised the hazard in their own minds, On January 27 1967, they paid the price for that lax atitude.