[X] My Assistant

[JRehling]

I don't know how many ghoulish incidents there are that have accidentally probed this issue for us, but I recall the incident in October 1999 in which a plane carrying golfer Payne Stewart and four others took off from Orlando, then apparently depressurized, killing them while the plane remained on autopilot until it ran out of fuel and crashed in South Dakota. Not much is known about the incident because the crash destroyed everything, but it seemed to be a case where sudden exposure to the atmosphere at 30,000 to 39,000 feet left the pilot without recourse to radio anyone on the ground before losing consciousness. Of course, he may have been distracted by other aspects of the situation and realized that calling the ground wasn't going to benefit the plane in the short run.

I read in a report on that incident that at 39,000 feet, the duration of one's consciousness is about 6-12 seconds. Once that last breath got pulled from your lungs, your streak across the surface of Mars might go sour pretty fast.

Another note: people have summited Everest without bottled oxygen. Now imagine you did have bottled oxygen; that would give you the same partial pressure as those climbers face at a pressure of only 70 millibars. And those climbers, of course, are doing something VERY HARD at the same time. It would seem to me that if you had 70 millibars of pure oxygen (or partial pressure thereof, and not enough CO2 to foul you up), you could go for a stroll, or maybe even a strenuous hike. When I say, "You", of course, I mean an elite high-altitude climber.

[dvandorn]

The research I've seen on this issue indicates that, even if you oxygenate your blood as well as possible (i.e., get yourself on the verge of hyperventilation), you can maintain consciousness in a vacuum or near-vacuum for anywhere from 15 to 30 seconds. Doing something strenuous that pulls the oxygen out of your blood faster (like running from one pressurized space to another) would tend to decrease your available time of consciousness.

So, in other words, the scene in 2001 *is* plausible, but sprinting on Mars for more than 20 or 30 feet probably isn't.

Someone should suggest this as a project for the Mythbusters, see if they can bust it or confirm it.

-the other Doug

[Bob Shaw]

Ooh. I'm not sure if I'd like to see somebody try to *seriously* stroll about on the surface of Mars without a spacesuit - I think you'd rapidly face a number of physiological brick walls, even if you were no couch potato. Even earache could be pretty disabling...

But, a quick sprint...

22-year-old Jamaican Asafa Powell broke the 100-metre record in Athens in 2005, doing the run in 9.77 seconds. And, perhaps of more interest to the UMSF crew, in 2004 Philip Rabinowitz entered the Guinness Book of World Records by clocking 30.86 seconds over 100 metres, demolishing the previous record of 36.19 set by the Austrian Erwin Jaskulski. Of course, both these athletes were 100-year-olds!

So, let's assume that nobody going to Mars will be able to equal the running ability of a top athlete - but could we match a centenarian? Far from 20-30 feet being doable, I think 20-30 metres is quite feasible for a reasonably healthy person, especially when it's in a 1/3G environment. Athletes should do even better.

If you're up and running as the big loading bay airlock door flips up then all the biological price/performance curves are still in the green - you're oxygenated, you're moving, and there's a chap with an oxygen bottle just a few yards away. Real show-offs will try to get ahead of the crowd by pole-vaulting (unless they're stopped in time by the Interplanetary Olympic Committee)!

Bob Shaw

[tty]

I don't know how many ghoulish incidents there are that have accidentally probed this issue for us, but I recall the incident in October 1999 in which a plane carrying golfer Payne Stewart and four others took off from Orlando, then apparently depressurized, killing them while the plane remained on autopilot until it ran out of fuel and crashed in South Dakota. Not much is known about the incident because the crash destroyed everything, but it seemed to be a case where sudden exposure to the atmosphere at 30,000 to 39,000 feet left the pilot without recourse to radio anyone on the ground before losing consciousness. Of course, he may have been distracted by other aspects of the situation and realized that calling the ground wasn't going to benefit the plane in the short run.

I read in a report on that incident that at 39,000 feet, the duration of one's consciousness is about 6-12 seconds. Once that last breath got pulled from your lungs, your streak across the surface of Mars might go sour pretty fast.

That kind of accident is typically NOT caused by explosive decompression, which is a pretty dramatic thing, but rather by a slow loss of pressurization. Slow hypoxia is very insidious and there have been any number of accidents where aircrew have lost consciousness without being aware of what was happening.
There was a recent case where a cypriot B737 took off with the automatic pressurization off and the crew and all passengers lost consciousness (the aircraft ultimately crashed). Admittedly the crew must have been pretty inept since they must both have skipped a checklist item and misunderstood or disregarded a pressurization warning during the climbout, but it shows that the symptoms are not obvious.

tty

[Guest_BruceMoomaw_*]

In fact, a former Air Force pilot recently sent a letter to our local newspaper proposing that, if we really want to carry out the death penalty (which he opposes) as humanely as possible, then using either a gradual vacuum chamber or a nitrogen-filled chamber is the best way to do it, because such deaths produce absolutely no pain or warning sensations of any kind -- our suffocation reflex is triggered by excessive CO2, not by inadequate oxygen. (Just before the first Space Shuttle flight, two pad technicians were tragically killed for just this reason -- they entered a chamber inside the Shuttle engine compartment that was flooded with nitrogen without their knowing it, and both quietly passed out and suffocated before they or anyone else knew what was happening.)

[JRehling]

or a nitrogen-filled chamber is the best way to do it, because such deaths produce absolutely no pain or warning sensations of any kind

Nitrogen, my old friend, after breathing 78% of you for all my life, you do me in now. Et tu, N2? Ack. Thud.

[MichaelT]

I always found the following NASA link very interesting:
Human Body in a Vacuum
There are also some references.

Though your blood will not boil this might still happen:
"The saliva on your tongue might boil, however."

So, if you have a tickling sensation on your tounge, beware!

Michael

[Rem31]

And what happens when you are trying to breath in on the Moon or on Mars (unprotected) without pressuresuit? And what is the pressure (in) a airplane during a passenger flight at 36,000 feet high? And what happens when decompression occurs then? (totally loss of pressure) inside the cabin of the airplane.

[Bob Shaw]

And what happens when you are trying to breath in on the Moon or on Mars (unprotected) without pressuresuit? And what is the pressure (in) a airplane during a passenger flight at 36,000 feet high? And what happens when decompression occurs then? (totally loss of pressure) inside the cabin of the airplane.

Breathing does sound iffy, I agree - if you have a mask over your mouth and nose and have an internal pressure of a few pounds then your ears and eyes would give you absolute hell. Perhaps an eye-band with sealed goggles and pressure-blanced earplugs would work, but it still doesn't sound like much fun, and if it went at all wrong it'd be crippling. A proper Flash Gordon bubble helmet, though, might just work (and could solve the UV problem). Add rubber swimming-trunks (don't ask me to spell out why that might be a *good* idea), and we're heading for comic-book heaven!

As for the questions you raised, most of them are answerd on the NASA site mentioned in the post before this one. The pressure in a 36,000 feet actual altitude aeroplane cabin can vary, but 10,000 feet is probably about right (it actually depends as much on the flight profile as anything). Total decompression then would result in ambient air pressure being the norm, and breathing being assisted via those little drop down cup masks they tell you about but never let you play with. You don't go BANG! You don't bleed from every orifice! You don't fall over dead!

Bob Shaw

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[tty]

And what is the pressure (in) a airplane during a passenger flight at 36,000 feet high? And what happens when decompression occurs then? (totally loss of pressure) inside the cabin of the airplane.

The pressure is about equal to being at 10,000 feet altitude. The reason it is kept at this level and not at sealevel pressure is to save power and decrease the strain on the pressure shell (which is very considerable). This altitude (10,000 feet) is normally quite safe for any reasonably healthy person (though I have seen people get altitude sickness at 11,000-12,000 feet).

If You have an explosive decompression there is one hell of a bang and the cabin fills with fog (since the thin air can't suspend nearly as much water vapour). The emergency oxygen masks should drop down, and usually they do. The crew (which have a separate, better and rather more reliable oxygen system) initiates an emergency descent. Normally this is fast enough to avoid casualties even if the oxygen system does not deploy. It is very rare for fatalties to occur in decompression accidents.
As a matter of fact in the case of the B737 accident I mentioned in an earlier post apparently most of the people were still alive but unconscious when the plane crashed and this was after a long flight at high altitude without pressurization.

tty

[MichaelT]

the cabin fills with fog (since the thin air can't suspend nearly as much water vapour).

It's a widely believed myth that air has a holding capacity for water vapor (even widely tought!). Due to the depressurisation the pressure of the air drops and, thus, the temperature of the gas water vapor. This finally leads to condensation.
For a thorough explanation go to the Bad Meteorology Page.

Michael

[Spacely]

Hey, guys. Long time lurker, first time poster.

This thread caught my eye and I thought I'd jump in with this "What if..."

Let's say you're wearing a parka, thick pants, goggles, ear plugs, an oxygen mask, and lying flat on your back in the Hellas Basin in mid-summer. Could you conceivably lay their all day (10AM to 5PM) without ill effects, or are the UV rays/solar radiation, etc. going to make you sick within hours?

[edstrick]

You die pretty fast. You're blood's above the boiling point, at any rate. Even with pressures high enough your blood doesn't boil, and with 100% oxygen, if the oxygen content in the air you breathe is too low, you pass out and die anyway.

There has to be documentation on "stay-concious" 100% oxygen pressure limit and "not die" pressure limit and it should be pretty findable, but it's above any plausible geologically recent martian surface pressure, i'm pretty sure. (not including transient atmospheres after major impacts or eruptions, etc.)

[Bob Shaw]

Let's say you're wearing a parka, thick pants, goggles, ear plugs, an oxygen mask, and lying flat on your back in the Hellas Basin in mid-summer. Could you conceivably lay their all day (10AM to 5PM) without ill effects, or are the UV rays/solar radiation, etc. going to make you sick within hours?

You forgot the rubber underpants.

Bob Shaw

[Rob Pinnegar]

You die pretty fast. You're blood's above the boiling point, at any rate. Even with pressures high enough your blood doesn't boil, and with 100% oxygen, if the oxygen content in the air you breathe is too low, you pass out and die anyway.

Hmm. So if your blood is above the boiling point, that means your lungs can't get any oxygen into your bloodstream?