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“It is deployed on the ocean floor next to deep coral reefs 62 feet (19 m) below the surface.” Divers - would a breach be fatal at this depth?

LeifCarrotson 4y ago
They're at "depth pressure", so a small breach would not be an implosion but a dribble of bubbles ascending from the station accompanied by an equal volume dribble of water into the station. If so, they probably have time to employ whatever their normal ascent plan is. If they were at atmospheric pressure, it could be a calamitous, crushing implosion, but if they had warning, 20m down and back up is a fairly straighforward freediving depth (he says, having only accomplished 12m personally). Unfortunately, they're not at atmospheric pressure, they're at 3 bar. Recreational divers can be at this depth for about 35 minutes and then will ascend slowly at about 10 meters per minute. Longer or deeper, and they'd be required to perform decompression stops, which is a whole different, much more dangerous animal: handling emergencies that don't allow immediate ascent changes the risk level from driving a car (just pull over if something goes wrong) to flying an airplane. If you spend an hour at 20 meters, you'd need to pause for about 15 minutes at 3m below the surface (so close! but it's a logarithmic stackup), breathing gently from your SCUBA system at this reduced pressure, waiting for gasses to dissolve safely and slowly out of your bloodstream. None of the dive tables I have access to cover saturation diving, so ascent after more than an hour - after a day, a week, or more - isn't covered. So, assuming they have access to SCUBA gear, they should stop at roughly 9, 6, and 3m from the surface on the way up for increasing amounts of time. All that said, failure to ascend to the surface will eventually be fatal; humans can't breathe seawater. Taking chances with the bends risks air embolisms that may cause a stroke or heart attack and be fatal, but if might not get unlucky; it's worth taking a chance!
bruce511 4y ago
It occurs to me that what they could do with is a Mr-like "escape capsule". A diving bell, moored to the sea floor, with slight positive buoyancy, on a mechanical tether would allow the aquanauts to ascend slowly if there was any failure in the habitat. I've not seen any information that such a thing exists, but a low-tech device like this would seem to be a prudent idea. On the other hand the habitat is at 19m, so even a small amount of steel walls are unlikely to suffer an "unexpected breech."
Gordonjcp 4y ago
Not a diver, but recreational divers often go down to that sort of depth on compressed air without any ill effects. You'd need to ascend slowly and hang about at ten metres and five metres for about ten minutes to let nitrogen out of your system, to get back to the surface. It's about three times normal atmospheric pressure so it's not going to be ideal if there's an accident, but it's not like going to smash you flat with pressure, it's not going to Byford Dolphin you.
- bonzini 4y ago
  As the other commenter explained, you absolutely need to do decompression for long-enough dives. The limit at 19m might be a few hours so it doesn't affect recreational diving, but in this case they exceed it. So if they had scuba gear they would have to stay at 19m and wait for help.
rich_sasha 4y ago
Sort of, yes and no. Divers dive with no pressure protection far, far deeper, certainly as deep as 100m and beyond. If the station floods but they have air to breathe, then that's fine. However, they are doing saturation diving. This means their bodies are full of dissolved nitrogen, which, if they were to ascend to the surface over any shortish frame of time, would regassify and kill them - that's "the bends". When ascending grona saturation dive, it takes hours to days, depending on depth, to surface. So if the station floods and they each have a scuba kit, they still can't surface and are potentially in trouble.
- junon 4y ago
  Just want to say, thank you for a very clear explanation :)
- rippercushions 4y ago
  If they can get the scuba gear on and attach themselves to something (rope between buoy and seabed etc) so they can control their ascent up, they could still decompress as long as they have enough new oxygen supplies being brought in.
- marcinzm 4y ago
  I'm wondering if due to the station being at the same pressure as outside a catastrophic breach is less likely. Slow flooding versus implosion.
  - rich_sasha 4y ago
    I was wondering that. I'm not sure. If there is a hole, the things that matter are the outside pressure and resistance to water flow. The latter is mostly viscosity I'd think and very little to do with air pressure on the inside. Whereas water pressure is 3x surface. That said 19m is really not that deep, I don't think it would be dramatically different to a leak closer to the surface. Some ships have draft of like 15m and, while generally holes in hull are bad, I'm not sure that this is some kind of special design precaution. But I wouldn't really know.

LeifCarrotson 4y ago

They're at "depth pressure", so a small breach would not be an implosion but a dribble of bubbles ascending from the station accompanied by an equal volume dribble of water into the station. If so, they probably have time to employ whatever their normal ascent plan is. If they were at atmospheric pressure, it could be a calamitous, crushing implosion, but if they had warning, 20m down and back up is a fairly straighforward freediving depth (he says, having only accomplished 12m personally). Unfortunately, they're not at atmospheric pressure, they're at 3 bar. Recreational divers can be at this depth for about 35 minutes and then will ascend slowly at about 10 meters per minute. Longer or deeper, and they'd be required to perform decompression stops, which is a whole different, much more dangerous animal: handling emergencies that don't allow immediate ascent changes the risk level from driving a car (just pull over if something goes wrong) to flying an airplane. If you spend an hour at 20 meters, you'd need to pause for about 15 minutes at 3m below the surface (so close! but it's a logarithmic stackup), breathing gently from your SCUBA system at this reduced pressure, waiting for gasses to dissolve safely and slowly out of your bloodstream. None of the dive tables I have access to cover saturation diving, so ascent after more than an hour - after a day, a week, or more - isn't covered. So, assuming they have access to SCUBA gear, they should stop at roughly 9, 6, and 3m from the surface on the way up for increasing amounts of time. All that said, failure to ascend to the surface will eventually be fatal; humans can't breathe seawater. Taking chances with the bends risks air embolisms that may cause a stroke or heart attack and be fatal, but if might not get unlucky; it's worth taking a chance!

bruce511 4y ago

It occurs to me that what they could do with is a Mr-like "escape capsule". A diving bell, moored to the sea floor, with slight positive buoyancy, on a mechanical tether would allow the aquanauts to ascend slowly if there was any failure in the habitat. I've not seen any information that such a thing exists, but a low-tech device like this would seem to be a prudent idea. On the other hand the habitat is at 19m, so even a small amount of steel walls are unlikely to suffer an "unexpected breech."

Gordonjcp 4y ago

Not a diver, but recreational divers often go down to that sort of depth on compressed air without any ill effects. You'd need to ascend slowly and hang about at ten metres and five metres for about ten minutes to let nitrogen out of your system, to get back to the surface. It's about three times normal atmospheric pressure so it's not going to be ideal if there's an accident, but it's not like going to smash you flat with pressure, it's not going to Byford Dolphin you.

bonzini 4y ago
As the other commenter explained, you absolutely need to do decompression for long-enough dives. The limit at 19m might be a few hours so it doesn't affect recreational diving, but in this case they exceed it. So if they had scuba gear they would have to stay at 19m and wait for help.

rich_sasha 4y ago

Sort of, yes and no. Divers dive with no pressure protection far, far deeper, certainly as deep as 100m and beyond. If the station floods but they have air to breathe, then that's fine. However, they are doing saturation diving. This means their bodies are full of dissolved nitrogen, which, if they were to ascend to the surface over any shortish frame of time, would regassify and kill them - that's "the bends". When ascending grona saturation dive, it takes hours to days, depending on depth, to surface. So if the station floods and they each have a scuba kit, they still can't surface and are potentially in trouble.

junon 4y ago
Just want to say, thank you for a very clear explanation :)
rippercushions 4y ago
If they can get the scuba gear on and attach themselves to something (rope between buoy and seabed etc) so they can control their ascent up, they could still decompress as long as they have enough new oxygen supplies being brought in.
marcinzm 4y ago
I'm wondering if due to the station being at the same pressure as outside a catastrophic breach is less likely. Slow flooding versus implosion.
- rich_sasha 4y ago
  I was wondering that. I'm not sure. If there is a hole, the things that matter are the outside pressure and resistance to water flow. The latter is mostly viscosity I'd think and very little to do with air pressure on the inside. Whereas water pressure is 3x surface. That said 19m is really not that deep, I don't think it would be dramatically different to a leak closer to the surface. Some ships have draft of like 15m and, while generally holes in hull are bad, I'm not sure that this is some kind of special design precaution. But I wouldn't really know.