 Immediately after the fire , NASA convened the Apollo 204 Accident Review Board to determine the cause of the fire , and both houses 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 . The astronauts ' rescue was prevented by the plug door hatch , which could not be opened against the higher internal pressure of the cabin . A failure to identify the test as hazardous , based on the fact that the rocket was <unk> , led to the rescue being hampered by poor emergency preparedness . 
