Aviation: I recently experienced hypoxia.

Don’t panic! I wasn’t flying at the time. It was part of some training to experience the effects of hypoxia (lack of oxygen to the brain). Ideally you would go into a decompression chamber for the most authentic experience but this involved wearing a mask that delivered a gas mix that simulated flying at various altitudes. At the same time I wore a device that measured my heart rate and blood o2 levels and performed a number of tasks to demonstrate the mental effects.

I think the most interesting/worrying thing to come out of it is that I, personally, didn’t feel much different from normal. If I was to become hypoxic in flight for real I think I’d have no idea. I did experience certain symptoms but I could only identify them in retrospect and wasn’t aware of them at the time. Also many of them were very subtle and would be drowned out by normal environmental factors.

The most obvious symptom was that I couldn’t hear much. The background noise faded away. However I was only aware of this when the noise came rushing back after I received some O2 for a while. Other than that I had a brief very mild headache and difficulty concentrating. I got a little flushed and sweaty but that is a normal symptom of mental concentration for me so I’m not certain it was a valid hypoxia reaction or just a reaction to being put in a small room and asked to perform various tasks for seven minutes.

One of the tasks was to remember the position of a playing card in a 2x2 grid of cards. Initially I thought that I just have a crap memory but thinking back on it, I had no trouble the first time when I had normal o2 levels, it was only later that I found it difficult. It was probably the most severe mental symptom as it presented almost immediately and was bad enough that I couldn’t even remember if the card being shown to me was on the previous grid at all. I distinctly remember looking at a 2 of diamonds and thinking that they’d done something to the font of the upside down 2 and also thinking that I remember there being a 2 of diamonds in the top left corner of the grid but I was certain that it had many more than just 2 diamonds, I.e., it had the numeral 2 on the top and bottom but had many more than just 2 diamond symbols.

My heart rate started at around 80 and gradually climbed to 110-120 through most of it, then there was a rapid drop to the low 60s at which point the instructor aborted the test as a precaution. Meanwhile my blood O2 levels started at around 98% and stayed there for a while before gradually dropping. At the point the test was aborted my O2 was about 50% and it continued to fall to the low 40s after being given recovery O2. This is known as the oxygen paradox. It takes some time for the O2 to take effect and you initially feel worse before you get better.

The whole thing was captured on video and I have a DVD that I can watch when I get home.

All in all a very interesting experience.

Pulse oximetry is cheap and easy. I wonder why pilots don’t wear an earlobe clip routinely.

This seems like a much cheaper way (compared to a hypobaric chamber) to teach pilots about hypoxia. Or is it somehow important for pilots to experience the actual pressure drop?

Apart from sudden dizziness when inhaling from helium balloons, my only experience with hypoxia was some years ago at the top of Pikes Peak (14,000+ ft): my fingers and toes were tingling.

I once flew in an unpressurized small commuter plane with about 12 seats. We had to divert over the Sierras in California to avoid storm clouds, which entailed going to 16,000 feet briefly. The pilots had oxygen, but the rest of us didn’t, and I got the full effects of hypoxia. It felt like alcohol intoxication, and I began to see large red spots blooming across my field of vision. It only lasted about ten minutes until we were back down to a safe cruising level.

I think it just fails the inconvenience/benefit equation. Although the risks from hypoxia are high, the chances of suffering from it are very low. When you’ve already got various warnings for monitoring cabin pressure and they will alert you before your blood O2 is affected, constantly wearing a personal monitor would get old very fast.

I can’t comment on the comparative benefits of the two methods. I would say that doing what I did was far better than just going over the theory in a classroom. On the other hand there is a chance that you will get some mask leakage which may result in you getting some normal air and perhaps lead to the effects being lessened. This can be controlled for with proper supervision though.

Here is where doing this kind of practical demonstration really shines. Machine Elf got tingling fingers and toes, Fear Itself got spots in his vision, while I got none of those things. It really drove home that you have to know your own symptoms.

Makes sense. Thanks!

IME with an altitude chamber the mild confusion came first. By the time I was getting visual symptoms we had one guy out cold and I couldn’t count to 5.

So for me at least the take-away was when something that ought to be simple isn’t, jump directly to hypoxia as a potential cause.

The real risk with the mild confusion IMO is the “aw fuck it, I don’t really need to be doing whatever; I’ll just sit here & daydream.” reaction. We were all trying to accomplish the various tasks set by the instructors. If I was at work & just idly fiddling with something mental or physical when I noticed I was confused it’d be easy in a confused state to simply dismiss the urge to continue to fiddle with whatever.

The good news is there’s not much way to have an oxygen shortage without a pressure shortage. And a shortage of pressure is real hard to ignore unless a bunch of warning systems all go bad after a bunch of safeguards also go bad.

For the airliner crowd:

Does the flight deck get real bottled O[sub]2[/sub] or just the chemical reaction toys the cattle in back get?

And: re. the cattle: does the FAA still insist that each one, including carry-on, still weigh 170#?
(at least they changed the 8 hr bottle to throttle rule)

I’ve been through the altitude chamber. It was fun. I wish I could do it again.

@usedtobe: All real bottled O2 in the cockpit.

IIRC people now weigh 190# in summer & 210# in winter.

We get bottled O2 and our BAe146 passengers also get bottled O2 while our Avro RJ passengers have chemical reaction units. The important difference is in the mask rather than the O2 production method though. Passenger masks are diluter masks that mix the O2 with ambient air. They are worse than useless for a smoke/fire situation and are only intended for use in a depressurization. The pilot masks are intended for smoke and depressurization and can deliver 100% O2 at a slight positive pressure to keep smoke out of the mask and goggles or they can dilute the O2 for depressurization. There is nothing inherently wrong with chemical reaction O2, our crew fire fighting PBEs use chemical reaction O2.

As far as I can tell the FAA is similar to CASA in that they don’t insist passengers weigh anything in particular. They do insist that your aircraft is correctly loaded and they provide some acceptable methods for doing this. Standard weights is one method as is using actual passenger weights. The standard summer weights currently acceptable to the FAA are:

Adult passenger: 190#
Male adult:      200#
Female adult:    179#
Child:           82#

For winter months add 5# to all numbers.

Details here.

The key point in all of this is that if you know your passenger load is non-standard, e.g., you have a plane load of sumo wrestlers, then you must use actual weights. Using FAA standard weights does not alleviate you from your responsibility of ensuring the aircraft is correctly loaded.

As for the bottle to throttle rule, I don’t know what the FAA have changed to. CASA still have the 8 hour rule but you also must be free from the effects of alcohol. So if I’m flying at 7am the next morning and I only want a glass of wine, the latest I can have it is 11pm. If I intend to get properly drunk then, well, I wouldn’t risk it. I’d only do it if I had a day off the next day. I’ve been subject to airport drug and alcohol tests a couple of times recently and my career is not worth a few drinks.


Just answered my own question. Hey. it does sometimes happen.