FAQ on Failures, Part Two: Apollo 1 Accident
Tim Nye
For more information on the Apollo program, I highly recommend the book Apollo: The Race to the Moon by Charles Murray and Catherine Bly Cox (Simon and Schuster, 1989, ISBN 0-671-70625-X). It is written from the point of view of the engineers who made the program work. This book is very difficult to put down.
The fire occurred during a 'plugs-out' test in which the astronauts were in the capsule atop the rocket on the launch pad. The test was a simulation of the liftoff countdown process. During the test a fire erupted inside the capsule, and the three astronauts died of asphyxiation. Only a most-probable cause was determined, and an account was given on page 190 of this book:
The door opened into the Environmental Control Unit (ECU). Just underneath it was a cable, part of the ECU's instrumentation harness. The cable was wedged against the bottom of the door by other bundles of wires beneath it. Each time the door was pushed shut, the edge of the metal door scraped against the cable. The slight but repeated abrasion had exposed two tiny sections of wire on the cable. Something -- maybe Grissom opened the door -- caused a brief electrical arc between the exposed portions of wire.
Even with the pure oxygen environment, the spark from the short would not have caused a conflagration. But it also happened that, just below the two scuffs in the cable, a length of aluminum tubing took a ninety-degree turn. This particular ninety-degree corner joint, one of hundreds in the tubing that interlaced the spacecraft, probably had sprung a leak. The joint had passed redundant inspections, but it had been subject to "creep" from stress at remote points in the system -- the spacecraft was constantly being worked on, and things got bumped around. Certainly even a small leak would help explain what happened, because the tubing carried a glycol cooling fluid which, when exposed to air, turned into fumes. The liquid was not flammable, but the fumes were.
The scuffed cable wedged against the bottom of the door was not originally intended to cross the tubing at the joint nor was it originally intended to lie quite as close to the tubing as it did. But there had been thousands of changes to the Block I spacecraft since the plans had been drawn, and the changes had put many cables, this one among them, in different positions from the ones that had originally been thought out at the design tables.
There was also some Raschel netting near the scuffed cable, closer than it should have been -- ASPO's directive about enforcing the fire rules had not yet been acted upon. Besides, astronauts had been customizing their spacecraft ever since the first Mercury flight. And there were so many rules. And this was just a practice countdown, not a real flight. And no on had focused on how highly flammable the netting was in a pure-oxygen environment.
Simpkinson surmised that the hot spot in the netting moved horizontally at first. Or it could have just hung there, slowly growing larger. Possibly it created an acrid smell. For about thirty seconds just before the crisis the crew wasn't saying anything but White and Grissom were moving around, doing something. One explanation is that they were trying to determine where the smell was coming from.
Heat rises. The glowing spot reached a vertical strand of the netting and began to climb, rising in temperature as it fed upon itself, finally bursting into open flame. It was at this moment, 6:31:04 PM (as later determined by the Medical Analysis Panel), that the sensors attached to Ed White registered "a marked change in the senior pilot's respiratory and heart rates." A second later, the first message came over Black 3, the crew's radio channel: "Fire," Grissom said, or perhaps it was "Hey." Two seconds later, Chaffee said clearly, "We've got a fire in the cockpit." His tone was businesslike.
Later on: "From the first call of fire to the final scream on the communications tape, from the sudden rise in the senior pilot's pulse to the explosion that slammed Jim Gleaves up against the orange door, just eighteen seconds had passed." An inspection of the construction of a sister capsule later revealed 1,407 errors.
