Why Hypoxia Awareness Training is Vital
by Eric Bradley, 01 January 2016

Despite more than 100 fatalities in recent years, hypoxia awareness training is still not a mandatory requirement for flight crew and cabin crew.

It is actually very important for crews to be aware of the danger presented by hypoxia and how to react to it. So even though it is not mandatory training, every airline should include it in the training curriculum anyway.

Hypoxia is a strange way to die, firstly because it's rare, and secondly because you don't know you're dying. There are different forms of hypoxia, but in the aviation context, hypoxia occurs when the concentration of oxygen present in air is insufficient to sustain life.

What makes hypoxia so deadly is that it's so subtle. Most people hearing about hypoxia for the first time would expect it to feel like drowning or choking. They would expect a dramatic struggle for survival, with lots of coughing, panicking, and struggling for air. But hypoxia is nothing like that.

The difference is that when you are drowning or choking, you're unable to breathe (asphyxia), and your body reacts violently to that situation. But with hypoxia, you're able to breathe perfectly well, you get plenty of air into your lungs, except the air isn't doing you much good because the oxygen content of the air is too low.

It's a problem because the brain isn't good at detecting this kind of situation. What the brain always does is to try to make the best use of whatever is available, which in this case is not enough.

So what happens when hypoxia sets in is that the brain doesn't generate a response to it, it just shuts down. How rapidly it kills will vary according to the actual oxygen levels and the fortitude of the individual.

Causes
The most common cause for hypoxia is partial or total loss of pressurization at high altitude. In modern aircraft, when the problem is due to sudden loss of pressure, this situation is usually detected and respirators will automatically be deployed. If the loss of pressure is due to a slow leak, however, it may not always be detected. This is called slow-onset-hypoxia.

There can be other causes of hypoxia, including the presence of substances which absorb oxygen from the air, or the presence of other gases such as carbon monoxide, carbon dioxide, nitrous oxide, helium, methane, and so on.

These could be present due to natural causes such as fire or some other kind of fault, or due to intentional introduction of them by a malicious passenger or crew member.

Symptoms
The onset of hypoxia in the body is usually accompanied by a slight headache, dizziness, and reduced peripheral vision. There may also be cardiac pain, which can vary in severity. At no time will you feel like you're not getting enough air, or that you are having difficulty breathing.

If oxygen is not restored promptly, total loss of consciousness will occur, followed by death. Some survivors report feelings of euphoria before losing consciousness, and recovered CVR dialog seems to confirm this. Affected flight crew sometimes seem to be quite exuberant just moments before they pass out.

Remedies
Cabin crew will not have much time to attend to passengers because the window from the first noticed signs of hypoxia to the point of unconsciousness is so short. If hypoxia is suspected and respirators have not automatically deployed, cabin crew should alert the flight deck.

If respirators are deployed, do a quick visual check to ensure passengers are not killing themselves and each other, then assist anyone that appears to need assistance if you can reach them. If there is not enough time to return to your crew station, find the closest empty seat and occupy it. Use the respirator as quickly as possible to avoid losing consciousness.

At the first suspicion of the onset of hypoxia, flight crew should don oxygen masks. PNF should notify ATC that there is an emergency and you are expediting rapid descent. PF should expedite descent, and there is no need to wait for permission because there really isn't time for that.

This is a problem if flying over mountainous terrain or in heavy air traffic areas. You need to do what you can to avoid flying into terrain or other aircraft, but if you do not descend immediately, there is 100% certainty that you are going to die.

Adding to the problem, you can expect to experience severe ear pain during rapid emergency descent, and in extreme circumstances the change in pressure can damage the internal parts of the ear, which could result in hearing loss.

Upon leveling off, PNF should request expedited emergency landing at the nearest available air terminal. When possible, check status of cabin crew and passengers. Alert ATC of any medical emergencies suffered by passengers and crew, and do your best to bring the plane down for a safe landing.