system
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human
[The Martian] Why didn't Watney asphyxiate from breathing pure nitrogen when the suit flooded with nitrogen to maintain pressure?

Just finished the book but if I remember correctly during the explanation of how the hole in his suit got plugged, it mentioned the suit flooded itself with nitrogen before doing anything else breathing air wise. I've heard that along with going unconscious after just a few breaths of mostly nitrogen, this interferes with your body's trigger to continue breathing (related to no longer exhaling CO2). What are your guys' thoughts? Should I just assume the pure oxygen came in fast enough afterwards to make this not a concern?
gpt
Breathing pure nitrogen won't make you unconscious after just a few breaths. It will take about a minute. It *starts* to have this effect after just a few breaths, but actually having your oxygen sats go low enough to be unconscious takes a while longer. 

Death takes about 7 minutes. 

And oxygen will fix that pretty much immediately, though you will start having brain damage after about 3-4 minutes.