An interesting issue has come up about a technical aspect of this story regarding Watney's breathing oxygen. A post on another forum has suggested that it would be hazardous to use pure oxygen for the hab over a long period
"Doesn't a long stay on Mars require lots of nitrogen gas? A person can't stay on pure oxygen the whole time right? There was mention of oxygen toxicity and making oxygen from CO2, but nothing of how the lost nitrogen was made up for. "
The answer to that should be that you don't need nitrogen or anything else to "make up the difference". You just breathe pure oxygen at a partial pressure equivalent to the % of oxygen in the atmosphere; 21% so that's about 3.1 psi.
However, the issue of the Apollo 1 fire then came up...
"Apollo One showed one problem with pure O2"
I fired off a quick reply to the effect that the real cause of Apollo 1 was an electrical spark, combined with the massive amount of flammables used inside the capsule, especially velcro and nylon netting, combined with the fact that the O2 level inside was at 16.7 psi, 2 psi higher than atmospheric pressure.
But now, I'm not so sure. Would the Apollo 1 fire have still happened if they had been breathing air, or breathing pure O2 at a partial pressure of 0.21 atm.