Shuttle Astronaut Mike Mullane on the Apollo 1 Fire

Mike Mullane on STS-41D
Mike Mullane on STS-41D

After reading my blogs about the tragic fire on Apollo 1, my former neighbor, Space Shuttle Astronaut Mike Mullane, and I exchanged several emails on the impact it had on him. Mike also had some questions about the accident, which sent me back to do more research. I discovered some new and surprising info (to me, at least) about the fire and its aftermath. I’ve summarized our discussions below.


Mike, this one about Apollo 1 was hard to write.  It’s about the fire itself.


I know what you mean about being “hard to write”.  Gus Grissom was buried at West Point and I marched in the funeral there.  It was my senior year.

As new astronauts [Mike was one of the first group Space Shuttle astronauts selected in 1978], we listened to the audio [of the communication with the crew during the fire] and it was disturbing to say the least.

That was a 100% O2 cabin, correct?  I’m almost certain it was.  The story I heard is that NASA, at the beginning of the space race, was worried about the anemic thrust of their rockets so they wanted to save weight by making the Apollo capsule as light as possible.

If you build it with a 100% O2 atmosphere the crew can survive with the pressure in the 5 psi range (I think.)  Lower cabin pressure meant a lighter structure to contain it and, thus, weight is saved.  I have no idea if all of this is true.  Do you?

In the Shuttle the cabin atmosphere was 14.7 psi with 80% nitrogen and 20% O2….a sea level Earth atmosphere duplication.  Obviously such an atmosphere significantly reduces the propagation of any fire that might start (in comparison to a pure O2 atmosphere).

Do you know if any of the Apollo missions flew with 100 % oxygen, or did the Apollo 1 fire motivate NASA to accept the weight penalty and go with a mixed nitrogen-oxygen atmosphere after that disaster?


Good question, Mike.  I did some more research.  Not sure about NASA’s concern about rocket thrust, certainly could be, though Werner Von Braun had been put in charge in 1960 and things on that front started getting better after that.

But from what I can tell, capsule weight was an issue.  Evidently, significant additional plumbing, and therefore weight, would be required if Apollo had to carry two gases (nitrogen and oxygen) vs. one.  (Obviously, NASA dropped that concern after the fire).  Also, Mercury and Gemini flights had been using 100% oxygen for several years and everyone was happy with it.

Plus, NASA was worried about the astronauts getting the bends from breathing nitrogen as the cabin pressure was reduced when they reached orbit (the plan was to go from 16.7 psi on the pad to 5 psi in orbit).

During an early test in a vacuum chamber, a pilot breathing a mixed nitrogen-oxygen atmosphere in a Mercury capsule got the bends and passed out.  In fact, during the Apollo 1 test, the cabin pressure of 100% oxygen was raised to 16+ psi to drive out any residual nitrogen before sealing up.

The real problem was that NASA et al had not thoroughly considered the flammability of cockpit materials with O2 at that higher pressure (not a problem when the O2 was at 5 psi).  Of course, that was a major flaw in their reasoning and when combined with the sloppy maintenance that caused the electrical short in the first place, it was a deadly one.

When the Apollo Command Module was redesigned after the fire, a number of modifications were made, but the cockpit atmosphere still wasn’t converted to “Earth atmosphere”.

It was changed to 60% oxygen / 40% nitrogen at 14.7 psi (that was still a fire risk, though not as bad as 100% oxygen), and the pressure was reduced to 5 psi when they reached orbit.  Following that, the nitrogen was then completely vented from the cockpit over the next 24 hours or so, leaving them with 100% pure oxygen again.

The astronauts’ suits were also sealed and pressurized with 100% oxygen starting several hours before launch, and they kept them on until they reached orbit, again to avoid the bends from breathing the nitrogen in the cockpit at launch.

So from this I gather that all of the Apollo missions were flown with 100% oxygen after they reached orbit.

Fascinating stuff, who knew? Glad you asked the question.  And since you informed me that Space Shuttle had an 80/20 atmosphere at 14.7 psi in orbit, it appears that the additional thrust of the Space Shuttle boosters, plus technology improvements in structural strength verses lighter weight, must have allowed all that fussing over the bends and 5% psi in orbit to go away for your program. Correct?


As to the answer about Shuttle atmosphere protocol, apparently the weight associated with a multi-gas system was not an issue since we did fly with a 14.7 oxygen/nitrogen atmosphere.  I know that one of the reasons this was preferred was to eliminate “variables” in cabin-mounted experiments.  Some experiments could be affected by a change in pressure/atmosphere making the data analysis harder for the scientists overseeing those experiments.


Apollo 15 Command Module in orbit
The redesigned Apollo Command Module in Lunar orbit (Apollo 15)

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Images NASA

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