The Math of "The Martian" Sol 40

Mark has a plan for getting rid of the excess Hydrogen in the Hab:

First he will move the live potato plants to the Rover to keep them safe. Next he will drop the temperature in side the Hab down to 1C, this will cause the bacteria growing in his soil to go into hibernation which will greatly decrease the amount of Oxygen they need to survive. Then he will trick the Hab's atmospheric regulator into bringing the Oxygen content in the air down to 1%. This will still be high enough for the bacteria to survive in their hibernation, but to low for the Hydrogen to ignite. Mark will breathe air from one of the spacesuit's supply tanks, and he will use another to add bursts of Oxygen to the air in the vicinity of an electrical arc made from the wires of one of his flash lights. This will allow him to slowly burn off the excess Hydrogen in the Hab without it all igniting at once.

Or so he thinks...

Mark has forgotten to account for one thing. Humans do not use all the oxygen in the air we breath. The air we exhale is still 15% Oxygen, as opposed to 20% Oxygen when we breath in. If the average person exhales 0.5 Liters per breath, and breathes about 20 times per minute under moderate exertion, how long until the Oxygen content of the Hab rises to 5%, enough for all of the Hydrogen to ignite at once?

The Oxygen Mark exhales might not evenly disperse through out the Hab immediately, so the concentration in Mark's vicinity might rise to 5% faster then the rest of the Hab does. To account for this, calculate how long it would take to increase the oxygen content of a 3 cubic meter volume from 1% to 5%.


And indeed the Hydrogen does explode after Mark exhales enough Oxygen into the Hab for it to ignite. Fortunately, Mark had already burned off a lot of Hydrogen in controlled burns before this occurs, also, there probably wasn't enough Oxygen for all of the remaining Hydrogen to react. None the less, the explosion was powerful enough to launch him across the room singe his clothing and cause minor injuries, but not powerful enough to kill him or damage anything important in the Hab.

After reviewing the logs of the atmospheric monitors, the event showed a momentary spike in pressure, as the explosion occurred, but then dropped back down to normal once all the Hydrogen and Oxygen combined into water. It also showed that the temperature in the Hab jumped from 1C to 15C and then stayed there. How much energy would be required to raise the temperature inside the Hab by 14C? How many moles of Hydrogen reacting would be required to release that amount of energy? How many Liters of water was created in this explosion?