Change in the Atmosphere

Expensive and time-consuming attempts have been made to fireproof the interior of the command module for the Apollo moon mission. Yet 13 of 28 fires deliberately started aboard the spacecraft during one series of tests this winter blazed furiously, thriving in the pure oxygen 16 lbs.-per-sq.-in. atmosphere that is maintained in the craft on the launch pad. Finally facing up to the real problem, NASA last week announced a decision to substitute a safer, two-gas mixture (60% oxygen and 40% nitrogen) during simulated and real countdowns on the ground.

With less oxygen to support combustion, tests have shown Apollo's interior to be indeed highly resistant to the rapid spread of flames. Within their closed space suits, however, the astronauts will continue to be supplied with pure oxygen; inhaled nitrogen would dissolve in their body tissues and cause bends at the lower pressures encountered later in the mission.

As the command module soars into orbit, the oxygen-nitrogen mixture will be gradually vented into space and replaced with pure oxygen at a pressure of 5.6 Ibs. per sq. in., enabling the astronauts to remove their helmets and breathe the spacecraft atmosphere. At this lower pressure, a pure oxygen atmosphere poses practically no fire danger to Apollo and its crew.

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