# How fast would you really lose consciousness in explosive decompression?

So you’re in a plane at 40,000 feet, and a door falls off. Or something. Anyway, when I read about decompression in planes it seems I always read “you’ll only have 8-10 seconds of consciousness to get an O2 mask on before you pass out.”

Why only 8-10 seconds? If I rapidly exhale and clamp my nose shut, I can stay conscious longer than that. Is this 8-10 seconds claim accurate? How long do the flight crew really have to get their masks on?

Well, here’s a whole page on it :

http://www.geoffreylandis.com/vacuum.html

It seems that the flaw in your plan is this :

Right now, where you live at full pressure, if you exhale fully, there is still lots of air left in your lungs. Your blood is still being oxygenated - and just importantly, not being dexoxygenated by low pressure - by this remaining air. So you remain conscious.

If you were to do this in a vacuum chamber or startled suddenly in an airliner, the air in your lungs is replaced with a near vacuum when you exhale. (not exhaling can easily outright kill you by freeing air bubbles to plug your blood vessels)

This near vacuum de-oxygenates the blood passing through your lungs, (membranes are 2-way) and so you actually only stay conscious until the blood that has almost no oxygen in it reaches your brain.

Oh wow. I did not know it would do that.

Popular Mechanics article about Jim LeBlanc, NASA worker, who got accidentally exposed to hard vacuum in a test chamber. IIRC, he had about 15 seconds of consciousness, and his last impressions before unconsciousness was that the saliva on his tongue was boiling. He lived with no permanent injuries.

However, a window or door opening (impossible btw but let’s just say a large hole is formed) .
Average person has 15-20 sec of coherent consciousness.
A healthy person, 30 seconds.
Assuming the aircraft were at 39000 ft and did not begin descending upon decompression.

It only takes it a minute or so to get to breathable altitude, all the while extending that consciousness timeframe, so assuming you are a healthy adult and the plane begins descending upon decompression there is about a 3-4 second window where you might start to be unable to think straight, but your chance of losing consciousness at all is pretty slim.

Btw it’s not like the movies. The volume of air in the pressurized chamber is pretty small and it equalizes with external pressure pretty quick with any sizeable hole. Sucking out a few lightweight objects like paper perhaps. Then just getting very windyand cold.

There is never a vacuum.

Look up quantas flight 30 or Alaskan md-80

Those coherent conciousness time frames are also based on elevated heart rates and things that happen when you’re scared.

So this is like running a mile or two, then holding your breath.

If the event is planned and you are calm, well, you could probably easily double or triple those numbers.

The real question here is USEFUL consciousness. Sure, you might not pass out for 20 or 30 seconds, but you’ll likely spend most of that time disoriented, unable to concentrate, clumsy, and generally not thinking straight. There’s a narrow window of maybe 5 or 10 seconds during which you can (A) remember where you are, (B) remember what you’re supposed to do, and © actually be able to do it. After that, you’ll be about as useless as a toddler, or a drunk person, or a person who is slowly waking up from a nap (all examples of people who are technically “conscious”, but can’t be counted on to do something like putting on an oxygen mask).

FWIW, air pressure at 35,000 ft is about 3.5 psi, which is 1/4 what you’re used to if you live in Memphis TN, or 3/10 of what you’re used to if you live in Denver CO.