The fire's ignition source was never determined, but their deaths were attributed to a wide range of lethal hazards in the early Apollo Command Module design and conditions of the test, including a pressurized 100 % oxygen pre-launch atmosphere, many wiring and plumbing flaws, flammable materials used in the cockpit and the astronauts ' flight suits, and an inward-opening hatch which could not be opened quickly in an emergency, and could not be opened at all with full internal pressure.

The fire's ignition source was never determined, but their deaths were attributed to a wide range of lethal hazards in the early Apollo Command Module design and workmanship, and conditions of the test, including: the highly pressurized 100 % oxygen pre-launch atmosphere ; many wiring and plumbing flaws ; flammable materials used in the cockpit and the astronauts ' flight suits ; and the hatch which could not be opened quickly in an emergency.

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