The air quality meter Rossi has indicates that the oxygen level in the container is 19.3% of normal, which would mean a total oxygen concentration of only 4.05% (normal oxygen concentration is 21%). Oxygen levels below 10% cause severe hypoxia, at 4% Rossi would be unconscious and near death, someone his age would likely pass out at around 10% (47.5% of normal).
Elias runs out of ammo after only firing 10 shots, the pistol he is using is a Glock 17 chambered in 9x19mm, which has a 17 round magazine.
Voit goes to pull the trigger on his pistol, but it doesn't fire because he is out of ammo. Yet the slide is not locked open, and he is able to pull the trigger. When a Glock, and virtually all semi-auto pistols, fires the last round in the magazine the slide locks open to let the shooter know the gun is empty, plus the trigger would be locked in the uncocked position, it would not be able to be pulled.