January 27th marked the ”plugs-out” test, where the command/service module was operating with all three astronauts inside under its own power, an essential test for ensuring the spacecraft’s flight worthiness. There was no fuel, no cryogenics, and no known potential hazard to this test. All three astronauts entered the module in fully pressurized space suits, while the cabin was pressurized and filled with oxygen. The three hatches — the removable inner hatch, the hinged outer hatch, and then the outer hatch cover — were then externally installed. A minor communications problem arose in the late afternoon, causing the simulated countdown to stall at T-minus-10 minutes. What happened next was very fast.
At 6:30:54 PM, while the crew was running through their checklist a second time, a voltage spike was recorded. Ten seconds later, at 6:31:04, one of the astronauts exclaimed something inaudible, perhaps “Hey!” or “Fire,” a transmission that came through Grissom’s microphone. Two seconds later, at 6:31:06, Chaffee’s voice was clearly heard, “We’ve got a fire in the cockpit.” Seven seconds after that, at 6:31:13, an unidentifiable, heavily garbled voice yells “[…] bad fire […] get… out […] [open ‘er/burning] up,” followed by an end to the last transmission at 6:31:22. The last image that anyone reported seeing before the transmission ended was Ed White reaching for the inner hatch handle, as the flames swept from left to right across the monitor.