"vulnerable wiring carrying spacecraft power" and "vulnerable plumbing carrying a combustible and corrosive coolant" A pure oxygen atmosphere at higher than atmospheric pressure 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) Ignition source The review board determined that the electrical power momentarily failed at 23:30:55 GMT, and found evidence of several electric arcs in the interior equipment. They were unable to conclusively identify a single ignition source. They determined that the fire most likely started near the floor in the lower left section of the cabin, close to the Environmental Control Unit. It spread from the left wall of the cabin to the right, with the floor being affected only briefly. The board noted that a silver-plated copper wire, running through an environmental control unit near the center couch, had become stripped of its Teflon insulation and abraded by repeated opening and closing of a small access door. This weak point in the wiring also ran near a junction in an ethylene glycol/water cooling line that had been prone to leaks. Electrolysis of ethylene glycol solution with the silver anode of the wire was discovered at the Manned Spacecraft Center on May 29, 1967 to be a hazard capable of causing a violent exothermic reaction, igniting the ethylene glycol mixture in the Command Module's pure oxygen atmosphere. Experiments at the Illinois Institute of Technology confirmed the hazard existed for silver-plated wires, but not for copper-only or nickel-plated copper. In July, ASPO directed both North American and Grumman to ensure no silver or silver-coated electrical contacts existed in the vicinity of possible glycol spills in the Apollo spacecraft. Pure oxygen atmosphere The plugs-out test had been run to simulate the launch procedure, with the cabin pressurized with pure oxygen at the nominal launch level of , above standard sea level atmospheric pressure. This is more than five times the partial pressure of oxygen in the atmosphere, and provides an environment in which materials not normally considered flammable will be highly flammable and burst into flame. The high-pressure oxygen atmosphere was similar to that which had been used successfully in the Mercury and Gemini programs. The pressure before launch was deliberately greater than ambient in order to drive out the nitrogen-containing air and replace it