Main article aside, I have to take the article to task for the section where they talk about an airplane and the oxygen masks that deploy when the aircraft depressurises and the passengers find it "hard to breathe".<p>Having gone through a depressurisation chamber as part of my flight training, at 35,000 feet (the normal cruising altitude for most passenger aircraft), it isn't actually hard to breathe. In fact, it feels quite normal. Your body just doesn't get enough oxygen into the bloodstream because the density of O2 in the stuff you are breathing in is so low, which causes onset of hypoxia.<p>The very reason why we do the sessions in the chamber - so that we can detect the symptoms of hypoxia particular to our own bodies, because there is normally no way to tell that you are no longer in an O2 rich atmosphere until you notice your fingernails turning blue and flashes of lights on your retina as well as feeling slightly tipsy (my own symptoms).<p>At higher altitudes (50,000 feet and up), then yes, there are issues because your diaphragm cannot create enough pressure differential against the outside air pressure to make you inhale and fill your lungs. My flight instructor was a test pilot in the 50's and 60's and he said when they were at that altitude, they were literally force fed liquid oxygen through their masks. They couldn't breathe it in, so they just had to open their mouths every few seconds and LOX would be shoved in (at freezing temperatures too, which used to dry out their nose, mouth and throats according to him).