Drysuit and squeeze question

[Subcooled]

In the early days of hard hat diving, with no check valves in place, when the surface compressor failed, the diver was crushed into a sloppy mess into the hard hat.

True, because the pressure inside the hardhat dropped to 1 ATM because of the failure. The external pressure then forced the diver into the hardhat. The end result was kinda messy. I've even heard tales of divers exiting through the air hose.

Same deal in the drysuit without air to equalize the pressure.

Nope. Cannot happen. The drysuit is not connected to the surface.

Your body is not compressible (mostly water) and there is already compressed air in the lungs. Because of that there is no pressure gradient either: water pressure and the breathing air/gas pressure cancel each other out. Thus, there won't be any nasty crushing or suction (some skin damage and mental breakdown possible).

Now, please, google "Delta P" for dangers caused by pressure gradients.

The drysuit will not contain an 1 ATM atmosphere. If your drysuit would have an air hose to the surface, and you would be sufficiently deep, up you would go. Through the air hose, I suppose.

In this sense, failing surface supplied air equipment can be more dangerous than SCUBA gear, although, in other hand, it gives you a seemingly endless supply of air.

 

[crofrog]

I mean it's pretty easy to just experiment with, I've gone down to 60ft before without adding any air just to see what it felt like... It was unpleasant because of pinching, but I wasn't getting "crushed" I just got vacuum bagged.

It did become a bit harder to move because of the lack of mobility in the suit and under garments, but I was still able to fin around some and hit the suit inflator without issue. No way I'd have been able to touch my valves though.

 

[Seaweed Doc]

Your breathing capacity would be maybe 30 % but not zero. This is widely experimentally proven in squeeze training/competitions in caving where people actually breathe (laborously) without being able to expand their chest. Enough to survive, enough to cause panic in the uninitiated.

Interesting. It seems I can do a bit of this sitting here in a chair and breathing very shallowly.

But then I got to wondering: If I can't expand my chest volume and inhale, what gets displaced? That new air has to push something out of position, or else will increase pressure in the lungs. And being forced to think about the pressure differentials in that case is making my head hurt. I'm not sure it's even anatomically possible to increase pressure in the lungs by simply inhaling and holding torso volume constant.

If I was sitting in a barrel full of water with a snorkel to breathe from, or even a tank, when I inhaled even a bit wouldn't the water level in the barrel rise?

 

[Seaweed Doc]

Drysuits can kill you. They need to be respected.

My line with students goes something like this:


Standard SCUBA equipment will do everything it can to keep you alive. (Note fail-safe modes, etc.)

Dry suits don't care if you live or die.

Rebreathers actively try to kill you.

 

[John C. Ratliff]

True, because the pressure inside the hardhat dropped to 1 ATM because of the failure. The external pressure then forced the diver into the hardhat. The end result was kinda messy. I've even heard tales of divers exiting through the air hose.

Nope. Cannot happen. The drysuit is not connected to the surface.

Your body is not compressible (mostly water) and there is already compressed air in the lungs. Because of that there is no pressure gradient either: water pressure and the breathing air/gas pressure cancel each other out. Thus, there won't be any nasty crushing or suction (some skin damage and mental breakdown possible).

Now, please, google "Delta P" for dangers caused by pressure gradients.

The drysuit will not contain an 1 ATM atmosphere. If your drysuit would have an air hose to the surface, and you would be sufficiently deep, up you would go. Through the air hose, I suppose.

In this sense, failing surface supplied air equipment can be more dangerous than SCUBA gear, although, in other hand, it gives you a seemingly endless supply of air.

Actually, that is not true, as the surface-supplied line is actually a low pressure line used now in hookah diving. This means that it contains pressurized air at somewhere around 120-140 psig. So no, current surface-supplied air cannot have the hazards of hard hat diving.

Hard hat diving used a compressor at the surface to supply air to the diver, but through a large hose that ran at the ambient pressure of the water; it was not pressurized much over water pressure at that depth. In the early days, it also did not have a non-return valve. Later variations provided a non-return valve that precluded the hard hat accidents that have been mentioned above.

SeaRat

 

[MrVegas]

But how could a dry suit exert so much force against a person's body (assuming that the diver had a functioning regulator system in their mouth and an adequate supply of air) that it would squeeze their body, boa constrictor style, to the point that would make it impossible to draw a breath?

Just out of curiosity, does anyone actually know if there is an answer to OP's question? I assume it would depend on a number of factors, but is anyone actually aware of any incident in which it was conclusively scientifically determined that drysuit squeeze prevented someone from breathing? Personally, I've been to 20 feet having forgotten to hook up my inflator, and certainly it's not uncommon to hit maybe 15 feet before using the inflator. A little uncomfortable, sure, but not painful. I was with another diver once -- in a neoprene suit -- who made it to 40-50 feet before hooking up his inflator. This should never happen, of course, but no one is perfect. There are posts on scubaboard where people have said they were much deeper than that. The point being is that the video the OP linked to is entitled "This Girl is Crushed by Her Drysuit." The Mills case was a terrible tragedy -- but there was a lot more going on than just drysuit squeeze.

 

[inquis]

Just out of curiosity, does anyone actually know if there is an answer to OP's question?

See post 2, 3, 6, 8, or other re-statements thereof.

 

[Vicko]

How is this hard to fathom?
There is no pressure differential, the dry suit is squeezing you because the volume on the inside is reducing to equalize the pressure with the outside as you descend. Once that volume gets small enough it starts to constrict you, leaving bruises and in extreme cases restricting your movement. Pressure differential can only happen in solid containers.
EDIT: Bad wording, continuous pressure differential would be the right term, it takes time for the volume to equalize.

Tec divers have been dying from this for the past 30 years, only this time it was not user error but clear instructor negligence.

In the MythBusters video the result is so violent because the equalization of pressures happened in a short time frame, the exact same thing is happening to you in a dry suit but at a slower rate.

The way to fix is is to
a) add gas to increase the volume on the inside
b) Add water to increase the volume on the inside, open your neck or wrist seal

I hate the dry suit speciality, but I see some of you need it.

 

[Wibble]

Just out of curiosity, does anyone actually know if there is an answer to OP's question? I assume it would depend on a number of factors, but is anyone actually aware of any incident in which it was conclusively scientifically determined that drysuit squeeze prevented someone from breathing? Personally, I've been to 20 feet having forgotten to hook up my inflator, and certainly it's not uncommon to hit maybe 15 feet before using the inflator. A little uncomfortable, sure, but not painful. I was with another diver once -- in a neoprene suit -- who made it to 40-50 feet before hooking up his inflator. This should never happen, of course, but no one is perfect. There are posts on scubaboard where people have said they were much deeper than that. The point being is that the video the OP linked to is entitled "This Girl is Crushed by Her Drysuit." The Mills case was a terrible tragedy -- but there was a lot more going on than just drysuit squeeze.

Post number 2.

You're effectively vacuum packed by your drysuit and cannot move. Injecting air into the drysuit frees it off and you can move again.

Vacuum bags are sold to compress clothing or pillows for storage. Its the same thing with a drysuit.

 

[eelpout]

I have been diving in a drysuit since 1979. Diving in Lake Superior and having ice on the lakes 4 moths of the year allowed me to enjoy the diving without getting hypothermic. Many years ago when I took my cave diving class at Ginnie Springs we had to swim against the current and pull ourselves down to the bottom (35 feet). I was so hung up on trying to get to the bottom that I never put air in my suit. I felt my suit squeeze but it didn't really bother me till I got to the bottom and then I added air to my suit. After the dive when it was time to take a shower my roommates who were all certified cave divers already were laughing at me. I asked why they were laughing, they told me to go and look at myself in the mirror. I did that and was shocked at what I saw. I was black and blue in my upper arms and my chest area. It didn't hurt but I finally realized how important it was to adjust the air volume in my suit the next time we dove the same site.