How much oxygen for a person to survive in an air-tight enclosure? (2004) | Hacker News Reader

How much oxygen for a person to survive in an air-tight enclosure? (2004)

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87 pointsgalfarragem62 comments

If you want to live in an air tight containers, you need to also be concerned about co2 buildup.

Wouldn't the co2 buildup kill you first anyway?

CO2 buildup will kill him far before all the O2 has been used up.

Even supplying fresh O2 into the room from a cylinder won't save him, unless someone finds a way to remove CO2 from the room.

It's useful to remember the makeup of air:

  78.1% nitrogen
  20.9% oxygen
   0.93% argon
   0.039% carbon dioxide

Carbon dioxide, in very approximate figures, is unpleasant at 0.5%, dangerous at 5%, fatal at 10%.

You're going to be doing pretty badly with half the oxygen gone even if you had no CO2.

What about venting some of the rooms air to space, and then releasing some O2 into it?

Came to say precisely this. Before you run out of o2 the co2 levels will likely render you unconscious, and will potentially also suppress your breathing.

I took a lungful (choked on the first breath, coughed, started really choking) of air heavy with co2 in a pub cellar once. Only because I fainted on top of the kegs above the co2 saturated air on the floor (leaky cylinder valve) am I here to tell you about it. Tastes like acidic metal and black velvet rushes in.

An other fun danger of insufficiently aerated rooms: in wine countries, until cellars aeration became more widespread a huge danger was CO buildup in cellars from fermentation, to these days people regularly die during initial fermentation, and a warning you get is "if you see somebody unconscious at the bottom of the cellar stairs you do not go down to help, you call the firefighters, trying to help just ensures they have two bodies to retrieve".

So, horror movies are realistic for once. If you see your friend lying dead in the cellar... GTFO of there, it really is zombies (or gas buildup of some variety) . :)

There are, sadly, lots of reports of farmers and their family members dying in manure pits due to a buildup of CO2 and methane. Someone goes in first and passes out, and then anyone else who tries to go in to save him suffers the same fate. In one case 5 members of a dairy farming family all died trying to save their father.

What if you hold your breath to help?

I've always been confused by this too - you'd think holding your breath would make it safe-ish.

I can only assume that it's still extremely risky because even if you remember to do it, you are very likely to misjudge how long you can hold your breath during an emergency situation with adrenaline pumping that requires you to drag someone up the stairs. Which means you get halfway up, end up forced to take a big deep breath, and pass out.

You could do that while lifting and carrying a 150 pound person up some stairs? Maybe if you had a rope with a slip knot, you could run down and put the rope around their body and run back up, then pull them up the stairs while trying not to hit their head on each step?

That would work if you have excellent breath-holding ability. But since you're exerting yourself by carrying an ~150-lb body, there is a risk you'll pass out because you're holding your breath. So you probably should take multiple trips, repeatedly moving the person partially and then returning to get good air. You should _slowly_ exhale all the while.

DO NOT hyperventilate before holding your breath and exerting yourself! Reason is, if you hyperventilate, then take a big breath, hold it and exert yourself you are likely to pass out _instantly_ w/o warning! [This was something we learned as kids - do not do this! You _will_ pass out (and you also risk embolism/stroke).

Why slowly exhale? Why is hyperventilating first bad?

I can take a guess on the exhale. If you're slowly exhaling there's less (no) chance you'll accidentally inhale.

If you hyperventilate your body can't tell how much air you have left.

"Why slowly exhale?" - So you don't increase the pressure in your lungs.

"Why is hyperventilating first bad?" - Should you hyperventilate and then hold your breath and any pressure is put on your lungs, YOU WILL PASS OUT! Don't do this!

Essentially hyperventilation reduces the blood's CO2 level. It becomes so low (while hyperventilating) that the body does not detect when the CO2 level subsequently rises to a dangerous level(while diving/holding your breath). The body fails to urge you to breathe fresh air and so you unwittingly pass out.

See the following two links for more info:

"The Choking Game: Self-induced hypocapnia": https://en.wikipedia.org/wiki/Choking_game#Self-induced_hypo...

Deep-water divers hyperventilate and then take a big breath immediately before they dive. Sometimes "shallow water blackout" (same as what happens to kids in the "choking game) occurs, endangering the diver:

https://en.wikipedia.org/wiki/Shallow_water_blackout

Are there carbon dioxide sensors that can be used in such cases like we have carbon monoxide and smoke detectors?

As others are saying - the CO2 poisoning will make you unconscious way before O2 runs out. You can train for it tho, much like freedivers do if you plan on surviving in airtight containers for longer periods of time.

There are also lakes which occasionally emit big bursts of CO₂. And, of course, it's denser than air, so you get an invisible flood of CO₂ pouring down the riverway... where people live. These can be thoroughly fatal.

Lake Nyos emitted a CO₂ cloud in 1986 which killed 1700 people.

https://en.wikipedia.org/wiki/Lake_Nyos

Pure nitrogen is even more dangerous because it feels perfectly normal to breathe it. You have no idea anything is wrong until you pass out, which can happen very quickly. Kind of a nice way to go, actually.

https://en.wikipedia.org/wiki/Inert_gas_asphyxiation

This can be alleviated with the use of CO2 scrubbers[0]. Basically you fill fan-powered canisters with minerals ("sodasorb" is a popular product used in the offshore diving industry), which absorbs CO2 from the atmosphere. That's not to say that you need to be able to remove and replace the minerals in the scrubbers every so often.

[0] https://en.wikipedia.org/wiki/Carbon_dioxide_scrubber

Out of curiosity, do you have an idea of the typical delay before saturating the filter? Do you have some pointer to space suits specification or something like this that I could read to have more information?

According to Wikipedia, "One gram of anhydrous lithium hydroxide can remove 450cm³ of carbon dioxide gas."[1] Also according to Wikipedia, a person produces some 1kg of the gas a day [2], which translates to roughly 550000cm³. That means around 1.2kg of lithium hydroxide per day per person.

The Apollo 13 LM canisters were rated for some 56 hours for two persons, but could only support three for less than 35 hours. That seems to fall somewhere between 5 and 6 kilograms, and apparently includes the scrubbers of the space suits onboard. Each suit was designed to support life for 6 hours (+ 30 minutes of emergency reserves) [3] which means some 350 grams of lithium hydroxide.

The longest EVA thus far lasted for just under 9 hours [4], for which you would need a bit more than 450 grams of lithium hydroxide. The Russian Orlan suits are designed to support life for between 5 and 7 hours [5].

An astronaut on an EVA might produce more carbon dioxide than the Wikipedia approximation, so you might want to round those numbers up.

Edit: I am also not sure how close to the theoretical maximum that absorption capacity is, so the numbers might really be somewhat optimistic.

[1] https://en.wikipedia.org/wiki/Lithium_hydroxide

[2] https://en.wikipedia.org/wiki/Carbon_dioxide#Human_physiolog...

[3] https://en.wikipedia.org/wiki/Apollo/Skylab_A7L

[4] https://en.wikipedia.org/wiki/Extravehicular_activity

[5] https://en.wikipedia.org/wiki/Orlan_space_suit

Thanks a lot, those are nice pointers.

Arguably, that was THE critical issue for crew survival after the Apollo 13 incident leading to the famous 'jury-rigged' CO2 scrubbing device improvised by the engineers on the ground

'Availability of lithium hydroxide (LiOH) for removing carbon dioxide presented a serious problem.'[1]

[1] https://en.wikipedia.org/wiki/Apollo_13#Crew_survival_and_re...

On an unrelated note - I read your term 'jury-rigged' and was thouroughly confused for a good minute. It sounded right in my head, but reading it on paper (screen) it looked wrong. Except looking up 'jury rigged' led to results about... Juries being rigged. Eventually I realized that the term I was looking for is 'Jerry Rigged':

http://www.merriam-webster.com/dictionary/jerry%E2%80%93rigg...

Which is 'probably a blend of jerry-built and jury-rigged', so now I don't know what to believe.

That's odd, the first two results for me when I search for jury rigged is a Google summary box with the definition and the Wikipedia article: https://en.wikipedia.org/wiki/Jury_rigging

Are you studying law or something, maybe Google is overly personalizing? :)

I got my parents a NetAtmo device it has an outside thermometer but also one for inside that also has a CO2 detector. It's amazing how often just my two parents plus one cat in a 5mx5m living room will cause it to reach near 1000ppm.

At Christmas time with about eight people it easily hit 1000ppm very quickly. Nobody else knew but I was watching the readings and it was interesting to see how that point it seems stuffy so a window was opened for some fresh air.

This is a 1970s single floor bungalow with forced air heating but no air exchange.

I had a theory this was what caused me to feel really sleepy when attending lectures. Wasn't sure how to prove it, though of course it could make sense with the right figures plugged in.

Would anyone be able to update his numbers accounting for co2 buildup? Are you thinking it would be a lot less time than he calculates?

A related question that might be interesting is in a container of a given volume that is perfectly sealed except for one hole to the outside air, and with no fans or other systems to encourage air exchange, how big does the hole need to be to keep oxygen levels high enough and CO2 levels low enough for survival indefinitely?

My intuition at first says that it would need to be a big hole because there won't be much airflow since the pressure inside and outside will be the same. But that is looking at it wrong.

It's the individual gases that matter. If CO2 is more concentrated inside than out, then there will be a net transfer of CO2 out. Similarly for O2 coming in. It's a diffusion problem, not an airflow problem, and I've got no usable intuition for that.

A interesting variant would be to make the hole intermittent. Assuming that my house is perfectly sealed when the doors are closed, do the normal openings for my daily comings and goings provide sufficient time for enough O2 to diffuse in and CO2 to diffuse out to keep my inside air breathable?

This is a question I've asked myself before too. Here's a back-of-envelope calculation which seems to suggest that diffusion alone will never be enough to keep someone alive inside a box. I'd be really interested to hear if someone can confirm or refute this.

Let's assume CO2 transfer is entirely diffusion-limited, i.e. the worst-case of completely still air. The diffusive flux of some gas-component (per unit area per unit time) J is governed by concentration-gradient (dn/dx) multiplied by a magic diffusion coefficient D, which depends on the molecular properties of the gas. For CO2 in air D = 1.6e-5 m^2/s. Let's assume the gradient is linear so dn/dx = (n_{inside} - n_{outside}) / length. Now n_{outside) = 0.04% * 1 kg/m^3 = 4e-4 kg/m^3. We should decide what level of CO2 we can tolerate, 0.5% should be on the safe side, so n_{inside} = 5e-3 kg/m^3.

Length is a bit trickier. If (a) we assume completely stagnant air inside and outside, length should be chosen as the size of the box ~1 m say. However if (b) we assume that inside and outside are pretty well-mixed individually, due by breathing, wind etc., then length should be about the depth of the hole, or thickness of the box-material, say 1 cm = 0.01 m. For case (a) CO2 leaves our box at a rate of about 7e-8 kg/s/m^2, for (b) 7e-6 kg/s/m^2.

From the original article, a human breaths .84 kg of O2/day, let's estimate a production of 1kg CO2/day (the extra carbon atom can't be all that significant), or 1e-5 kg/s.

To compute the area of hole needed to maintain 0.5% CO2, we just divide 1e-5 by J, to get the area. In case (a) we need an enormous area of 135 m^2, in (b) "only" 1.35 m^2.

This seems to suggest that "air-holes" must work (if indeed they work at all) with air-flow. This doesn't necessary require an over- or under-pressure in the box - a suction can be generated by wind passing over a box with holes on both sides - this process would be far more efficient at restoring atmosphere than diffusion. But would be less reliable.

Heat is another helper here. Body heat would eventually cause a chimney effect unless the single hole is on the bottom of the box. That will create an air current, greatly increasing the speed of diffusion.

Your result of "0.042 day" is also known as "an hour."

Or four centidays.

or, when multiplied by 1000, perhaps something else...

...Life, The Universe and Everything.

What? Nobody read The Hitchhiker's Guide to the Galaxy? Heck, it was also the first computer game I ever played.

What about the scene from pirates of the Caribbean where they walk underwater in an upside down rowboat. Is that realistic?

Not even in the slightest. Yes, i understand this was probably a joke, but still. That scene was pretty dumb.

Actually there's nothing dumb about the scene, except that there would be an upward pressure on the boat (buoyancy).

If that was overcome (e.g. with some weights or strings holding it down), it would be perfectly fine to breath in there for a while.

So, aside from the buoyancy issue, not only it's not "dumb", but that's exactly how old "diving bells" worked.

https://en.wikipedia.org/wiki/Diving_bell

Really... you take issue with some exaggeration in buoyancy physics over the undead pirates?

It's pretty normal to be more bothered by casual violations of the way the world works than by fantasy elements. It's similar to the Uncanny Valley. With fantasy elements, our suspension of disbelief allows us to accept them as part of an alternate set of rules for the world. But when a part of the movie that seemed to be the same as the real world suddenly behaves differently, that can be off-putting and feel inconsistent. For example, if a character couldn't carry a small bucket of water but could carry a large man, many people would read that as an inconsistency rather than just accepting it.

I hate this argument. Fantasy movies are expected to be internally consistent. That means they follow the fantastical rules they set down, and they otherwise follow normal real-world rules.

(Though I agree with coldtea that the PotC scene wasn't that bad.)

If you're asking about the oxygen levels, I'd say so. At a rough guess of 1m^2 of oxygen per person in the boat, for two people. That's an hour of walking according to the article. (Assuming water takes less oxygen to walk in)

I think it'd float to the top though. It'll need some kind of weight...

A one ton metal boat shaped object would do:

http://kwc.org/mythbusters/2007/11/episode_92_pirates_2_row_...

The CO2 buildup would kill them long before they reach the 17.5% O2 mark. And considering how hard it is to actually walk in water, i'd say it would almost be equivalent to working out. According to the article, a person that is heavily working out would have 10 minutes to reach the 17.5% mark in a 1m^3 area. So maybe 20 minutes for the boat people? And that is neglecting the CO2.

Except both oxygen and CO2 diffuse in and out of water so that buys you time, especially if the water current is constantly keeping the concentrations equalized near the boat.

Nitpick: s/1m^2/1m^3

> I think it'd float to the top though. It'll need some kind of weight...

A simple way of thinking about it is that boats float because they contain air (rather than water). The fact that they are upside down or the right way up changes little.

Since the rowboat can support two people, it should definitely float to the surface, dragging them along with it.

> Since the rowboat can support two people, it should definitely float to the surface, dragging them along with it.

Only if the air bubble occupied the entire inner portion of the hull. If it were, say, only half the volume of the hull - I suspect it would be neutrally buoyant with the weight of two people.

People are roughly* neutrally bouyant in water. Thus they don't weigh anything when submerged. Otherwise swimming would be very hard indeed. So you would need to weigh down the boat to sink all that air and wood.

*depending on depth and body composition, but give or take a bit, neutral.

Agreed, but boats when not filled with air are typically negatively buoyant. I'd wager that there's an air bubble small enough to make the whole system negatively buoyant, but large enough to sustain the people breathing it for some period of time.

The first diving bells didn't have a system to refresh the air supply, they were still used for meaningful work.

https://en.wikipedia.org/wiki/Diving_bell

They tested this on mythbusters- http://www.discovery.com/tv-shows/mythbusters/mythbusters-da...

Works fine in a universe that allows for magically undead pirates....

Because CO2 dissolves well in water, diving bells work much better than intuition says them should.

But then, I'd expect the boat to break much sooner than they get out of air, or even completely under water.

Well there was that cook who survived for 3 days in an air pocket inside a sunken fishing boat. At the time there was a lot of discussion what made that possible. I believe it was posted to HN as well but can't find it:

http://www.huffingtonpost.com/2013/12/05/cook-survived-sunke...

I'm reminded of A Pail of Air by Fritz Leiber.

Twenty thousand leagues under the sea had an interesting part about the same problem.

Whoa whoa. This means Sunshine wasn't scientifically accurate?!

Would be nice if this calculation were in iPython notebook or Cruncher (https://www.cruncher.io/).

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