Drysuit and squeeze question

[OMyMyOHellYes]

First up, my knowledge of drysuit (or even slightly chilly water) diving is limited. I simply have less than zero interest in ever getting into water cooler than 80 deg F.

But I was watching a yootoob on the death of Linnea Mills during a drysuit training exercise. Tragically bad mojo and galactic-class CF all around. But there was one thing that stuck out and baffled me from that video. IIRC, there was one guy who was trying to go after her as she was sinking and reported that her uninflated suit was squeezing her so hard at 85 feet that it seemed she couldn't draw a breath. (9:05 into the linked video)

With my rudimentary, marginal knowledge of drysuit things, I could see a person getting pinched if there was a fold of skin in a wrinkly part that was getting squeezed, and that could cause injury I suppose. 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?



An uninflated drysuit, at any given depth, cannot exert any more pressure against a diver's body than the ambient pressure. If one were to try and breathe atmospheric pressure air at depth, I get that that ain't gonna work. So we have regs and a pressurized air source that cancels that differential out.

Pressure at 85' exerted on a diver's bare skin ~ 37-38 psi. Pressure transmitted to the external surface of the drysuit ~37-38 psi. The pressure of the interior surface of the dry suit against a diver's skin ~37-38 psi. First stage IP ~120-145 psi equalized to ambient would have the air in lungs pushing outward ~37-38 psi.

Was that narrator or diver that was trying to help wrong in the assessment that she was squeezed to the point of being unable to draw air? Maybe out of air or other malfunction, but drysuit pressure?

Am I missing something?

 

[arbby]

It's not ambient water pressure acting against the diver, but that the pressure in an unequalised drysuit is at a lower pressure.

Effectively it is vacuum packing where the lack of give will eventually prevent lung expansion. Think of vaccum packed food items which are solid until you open them.

 

[MidOH]

1 pound of pressure differential, multiplied by the surface area of the object, can equal a ton of force.

A door with only an ounce or three, of pressure differential, is impossible to open. One of my customers used to have a habit of trapping herself in an unlocked generator room. Once the gens started moving air, the doors could not be opened. And that's part of why the code says doors have to open out. If they open in, as soon as you turn the knobs, the door rips open and breaks your nose (true story).

A dry suit is a ton of surface area. If it doesn't tear, I have no doubt that could hurt.

The actuator on a semi trucks air brakes, is only 5-8" across, and needs pressure no more than a diver sees in the water.

 

[davehicks]

In a wetsuit the water enters and gets of both sides of the fabric, equalizing the pressure. In your lungs and sinus, the regulator equalizes the pressure of your airspaces and the outside water enabling you to breath. In a dry suit the water cannot enter, and the pressure squeezes it tight. This is why there is a LP inflator hose from the regulator allowing you to equalize, just as with your lungs.

Try this in a sink with your hand in a garbage bag. Plunge your hand in and see what happens.

 

[arkstorm]

The drysuit acts as an unequalized air space, same as your mask.

Think about what happens if you don't equalize your mask, now multiply that force by the square surface area of the drysuit.

 

[inquis]

Friction makes it increasingly difficult for skin to slide beneath the fabric. This sliding is required in order to breath (torso expands) or typically to move an arm to activate a suit or BC inflator (assuming it were functional).

 

[JohnnyQuest]

Watch this. Different suit, same physics.

 

[Subcooled]

As the ambient pressure increases (and hence the pressure inside the suit - they are equal because the suit is not a pressure vessel but made of flexible cloth) the air inside the suit gets compressed. This allows the suit fabric to come closer to your skin. You may wear some undergarments, winter overalls and such, and as the clothing gets compressed and stiffer (or, in the worst case scenario, the drysuit hugs the naked skin), you movements become more and more difficult. If this causes panic in you, you're gone.

Note, that your skin is flexible. It allows for movement. The suit is not flexible. Add friction. See the problem?

In a wetsuit you have pressurized water on both sides of the wetsuit. Water does not (practically) compress, but the wetsuit will compress and get thinner. It won't get pushed against your skin though. And in any case, neoprene wetsuits are also more flexible than trilaminate drysuits. I am not an expert on wetsuits, though.

I once had a little mishap with my drysuit, and the only thing I could move, somewhere between 60 and 90 ft, was my wrists to send a distress signal with my light. Not fun, I must say. Pressure in the lungs is the same as outside, so one will not get crushed, and the diaphragm can do its work inside the rib cage. Fully inhaling might become difficult because of the cloth of the suit. This would only allow for partial breathing and would make CO2 control a challenge. This is something cavers are intimately familiar with. Some of us actually enjoy some amount of squeeze, with the breathing techniques necessitated:

 

[Subcooled]

Watch this. Different suit, same physics.

In this video the backpressure valve of the helmet has failed (and the pump too). In this case the pressure inside the helmet is 1 ATM and outside maybe 6 ATM. And guess what happens. Now, your drysuit (helmet) will not have a hose connected to the surface unless you are a commercial diver.

 

[Rogerdiv]

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