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Comment by jlgreco | Hacker News Reader

Does anyone know how survivable rapidly surfacing from 30 meters would be? Wolfram Alpha has the pressure down there at almost 400 kPa (compared to 100 kPa) so my suspicion is "not at all", but I'm not really familiar with the tolerances and life expectancies with the bends.

30 meters is just agonizingly close to the surface though, well within what most adults could do horizontally (particularly if their life depended on it.) Being that close to the surface, but still so far away, must be absolutely awful.

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It depends on how long you've been down there. If you have just been dragged under water with your boat, it's probably safe to make a rapid ascent (don't hold your breath though) - in fact, diving school teaches emergency ascents for situations where no other options apply, even if the diver is in need of decompression. However, after about half an hour it becomes a serious problem that gets worse over time as gases start to infuse into the tissue.

If rescue (and access to a pressure chamber) is available right away, I'd make that ascent immediately even after being down there for a longer time. It beats drowning or CO2 poisoning.

Dive tables illustrate pretty well how the relationship between depth and time works: http://www.naui.org/tables.aspx

Do you really have to pay attention not to hold your breath while ascending?

I'd have thought you'd feel your lungs expanding and you'd have the reflex to let the air go away. Although on the other hand it's probably not a situation common enough for us to have evolved an inate reaction to it.

Yes and no. If you relax your breathing apparatus, air will escape naturally. However, if you actively hold your breath, the mounting pressure can actually lead to a tighter block. Rapidly expanding lungs are not something that falls within the daily experience of most humans, so it's best to be aware of the complications. Especially when panic sets in (and the journey upward from 30m will be quite long) it can cost a lot of self control to force yourself to exhale.

Especially since if you're doing an emergency ascent, it's quite likely that it's due to having problems with getting air from your cylinder (if your air supply was fine, you'd probably be doing a controlled ascent instead). It's very difficult to avoid holding your breath when you know you won't be able to breathe in again until you reach the top.

Yes for at least two reasons. Firstly, holding your breath can cause you to pass out. Secondly, holding your breath while the pressure is decreasing can cause an embolism (air can enter a blood vessel in the lung) which can form a clot and kill you: http://en.wikipedia.org/wiki/Air_embolism#Gas_embolism_in_di...

Whether or not you have the reflex to let out the air, the complications are pretty severe, so it's worth covering either way!

You do..(though it's simple, you just sort of humm or go "aaaaah" to yourself, silently.. that keeps your airway open).

No innate reaction - over-inflation would require a positive pressure applied to the lungs - normally as we breathe it's at equilibrium. Your lungs aren't elastic at all - once they are at capacity, over-pressure will rupture them right quick, and you own't feel it coming (but you'll sure feel it happening)

The Royal Navy has a 30m deep "pool" (more of a water filled tower) that they use for submarine escape training:

http://en.wikipedia.org/wiki/Submarine_escape_training_facil...

So it must be fairly survivable.... Maybe it's staying for a long time at that pressure that causes the problem?

They no longer use it - too many people were dying in the training, and modern submarines go much deeper anyway.

If you want to have a go, you can go to Nemo33 in Belgium still.

The too many seems to be 2 death in 60 years with up to 4500 trainee a year during the 60s/70s.

Cf : http://www.worldnavalships.com/forums/showthread.php?t=3787 http://www.subescapetraining.org/History1.html

Florida has inland freshwater springs with depths to 240 feet / 73 meters. I did my first deep water scuba cert in Ocala:

http://www.adventuresunderthesea.com/scuba-class-information...

The deeper you go, the less time you can stay there before you have to control your ascent.

Even a mild case of the bends can be excruciating, not something you can tough out: http://en.wikipedia.org/wiki/Decompression_sickness

Time at pressure is the key, without question.

The longer you breathe at pressure, the more time there is for gas (nitrogen, mainly) to saturate your system (until you are at equilibrium, anyway).

Release the pressure, and it's like opening a can of soda... all that dissolved gas can't stay dissolved any longer.

It takes time to get out of your system as you reduce pressure, so a gradual decompression is the only safe way out once you are saturated.

In a typical submarine, air pressure is maintained at standard atmosphere, relying on structural integrity to keep all that pressure from crushing the ship. That means they can surface any time without risk.

Another neat thing when diving is that if you are down at 30 meters, you can take a breath from your regulator, spit it out, open your airway gently (say "AAAAH" quietly to yourslef basically) and then ascend, you feel like you have an endless supply of air, because that breath you took is expanding on your way up. (That's part of recreational diving.. you can ascend from 30 meters on a breath of air and not get stressed out about it)

Completely survivable. It's really not that deep (breath hold free divers do it routinely), and any sickness he would have could be easily treated in a pressure chamber (most large hospitals have them).

It's not necessary to get into the chamber instantly - symptoms don't start for 1 to 48 hours.

Free divers actually avoid the decompression problem altogether. They breathe in air at surface pressure, it compresses as they dive down, and uncompresses to the same size as they rise up. The air cannot bubble out of their blood.

The problems arise when you breathe in high pressure air down deep and bring that air up with you.

While it is highly unlikely that a single free-dive would cause a symptomatic decompression injury, there is a high incidence of decompression-related injuries amongst free-diving fisherman due to repetitive and deep free-diving. The probability of decompression sickness occurring is related to time and depth.

Here's a link that provides a number of references: http://www.thediveforum.com/dive-medicine/3706-long-term-phy...

I don't think this is exactly true in extreme cases. You go down deep enough and weird things happen.

That's actually not why they avoid the problem.

It's a matter of time and volume - it takes time for nitrogen to dissolve and they are not down there long. And they only have a single lungful of air, so there is not a lot of volume to dissolve.

But, if they do repeated dives, each one will dissolve more and more nitrogen until they do have problems.

A few weeks ago I was on a navy submarine. They explained the escape procedure and I asked how survivable it was. Apparently nobody has much faith in it, but its better to try than certain death by drowning.

... I did wonder how painful a fast ascent from the bottom of the ocean would be once the bends kicked in, but had enough sense not to raise this question with about a quarter of the crew in earshot.

The insides of submarines are at roughly 1 BAR. Unless there is a breach of the integrity of the submarine and you manage to stay in a compressed air pocket for a sustained amount of time (unlikely, at best) prior to ascent, you will not have gas disolved into your tissues and thus won't get bent.

No, but 1 bar air in your lungs can be quite a proposition at any significant depth. Not for the faint of heart.

Can you clarify what you mean by this? As I type this comment, I have about that density of air in my lungs, and it doesn't particularly trouble me.

One atmosphere in your lungs, ten atmospheres outside your lungs --> scrunch.

For an approximate simulation, imagine what removing 90% of the air from your lungs might feel like.

That's not how flexible containers work. In the presence of increased pressure, the guts press against the diaphragm, which compresses the lungs.

I don't have to imagine what removing air from my lungs feels like: that is part of breathing! Anyway, this guy seems to do OK compressing his lungs even more:

http://competition.the-french-job.com/spread-the-world-recor...

If the increased pressure is high enough, your diaphragm and lungs are going to be in a world of hurt.

Physiological freaks aside, go too deep, and you're dead. Especially when you go from 1 bar to, say, 15 instantly, which is a situation that free divers do not expose themselves to.

It's not just your lungs though...

You know that pain you get in your sinuses and ears and other air-pockets in your body when you swim to the bottom of the deep-end of the pool? That's from a pressure difference of like .3 bar. Now imagine something 10 times that.

If your lungs contain 1 bar, and water around you is 10 bar, you will be very uncomfortable.

One would imagine that any escape procedure from a submarine involves some type of airlock and some type of air breathed in at the pressure for whatever depth you are at.. otherwise you'd just be unconscious from the pain instantly.

At 30 meters the pressure is 4bars (10m of water a 1b plus the atm). Your lungs contains ~7l of air, so with Mariotte lawsm you've got: 7l4b = cte = 28l1b. This means that if you don't expire when you swim up to top ... your lungs will contain 28l of air ... and explode! That's a common diving danger, and the cook certainly didn't know it.

If only nature designed our lungs with a hole that can be used to fill and empty them, rather than the completely hermetically sealed ones we have!

If you're holding your breath, which a naive swimmer likely is, then it's perfectly possible to rupture parts of your throat when the pressure differential grows too large. I'm not sure if that'd be fatal or not, but it'd definitely be dangerous.

The pressure differential, in this case, was three times that between normal pressure and vacuum.

The pressure differential for vacuum isn't enough to be dangerous by itself. The dangerous thing about vacuum exposure is that at that pressure your blood will boil at body temperature.

That's what they teach in diving class, but I've always wondered if the pressure wouldn't cause an impulse to exhale at some point?

Nope - the impulse to exhale comes from carbon-dioxide levels, not pressure in the lungs.

You'll go from feeling fine to acute pain to very dangerous damage pretty much momentarily.

A hole at one end. Put an empty, open bottle in a bowl of water facing downwards - where does the air go? Nowhere.

To be fair, the lungs compressible and more like a balloon than a bowl of water.

I can assure you, you can exhale upon ascent when inverted. (source: me, who used to log plenty of hours below 150fsw breathing mixed gasses).

Of course. But if you don't exhale deliberately you still risk barotrauma (I am a diver too see).

30 meters is around the commonly accepted limit for recreational scuba diving.

If you are diving you can take a breath of air from your regulator at 30 meters and then, keeping your airway open, ascend to the surface on a single breath. Because you are ascending, the air in your lungs expands as you go up, and you get to the surface with a full breath of air, even though you've been blowing bubbles all the way up.

At 30 meters you limit your dive to 20 minutes... beyond that you risk decompression sickness. At 10 meters the limit is around 3 hours.

In both cases, if you were down for a couple of days, you'd need decompression. The deeper you go, of course, the more dangerous it is as there is more dissolved gas.

Probably not very survivable, given that they stuck the guy in a decompression chamber for 60 hours.

Well yeah, but even a slight chance would be worth attempting if you were in such a position, even if it were just a 5% chance of survival, compared with the 100% chance they were probably shooting for with the 60 hour decompression.

Of course if attempting it meant certain but excruciating death, then taking a shot at it would not be the way to go.

They left him in there for so long because he was in the water for so long. (i.e. plenty of time for nitrogen to dissolve).

If he had swum up right away he would not need decompression.

I imagine in the dark he would have been too scared of not being able to find the way out in the cluttered sunken vessel.

He probably also didn't know how close to the surface he was.

It would be inadvisable if you were down there for any length of time, but survivable.

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