That Grissom “accident” was strange one indeed.
Which killed Senior Pilot Ed White, and Pilot Roger B. Chaffee as well. Rushed too much to disallow high probability of risk.
Immediately after the fire, NASA convened an Accident Review Board to determine the cause of the fire, and both chambers of the United States Congress conducted their own committee inquiries to oversee NASA's investigation. The ignition source of the fire was determined to be electrical, and the fire spread rapidly due to combustible nylon material and the high-pressure pure oxygen cabin atmosphere. Rescue was prevented by the plug door hatch, which could not be opened against the internal pressure of the cabin. Because the rocket was unfueled, the test had not been considered hazardous, and emergency preparedness for it was poor.
A pure oxygen atmosphere at higher than atmospheric pressure - with the cabin pressurized with pure oxygen at the nominal launch level of 16.7 psi..The high-pressure oxygen atmosphere was similar to that which had been used successfully in the Mercury and Gemini programs.
A cabin sealed with a hatch cover which could not be quickly removed at high pressure
An extensive distribution of combustible materials in the cabin
Inadequate emergency preparedness (rescue or medical assistance, and crew escape)
An ignition source most probably related to "vulnerable wiring carrying spacecraft power" and "vulnerable plumbing carrying a combustible and corrosive coolant"