Thread: The Squeeze
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Old 15 July 2009, 08:53 AM
hix1050
 
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Classically, "squeeze" is a feature of hard-hat diving, and is a regular topic in books about marine salvage, as it is a constant threat to the diver. Rear Admiral Edward Ellsberg's books come to mind. See http://www.edwardellsberg.com/
Background for the "Standard diving dress" is at http://en.wikipedia.org/wiki/Standard_diving_dress

There are two mechanisms for squeeze.

First, the air line supplying pressure to the diver's helmet fails catastrophically, and the pressure of the water abruptly extrudes the body of the diver into the helmet. The engineering solution to this is a check valve at the helmet, so while the story from 'A Brief History of Everything' may be partially true, and may well have occurred once or twice, I expect that it is mostly legendary now. That the diver's body would be completely extruded into the air line doesn't survive close inspection, as 1) the viscosity of the tissues is going make pushing them up the narrow line very difficult, 2) sooner or later a piece of bone would get jammed in the hole in the helmet where the air is exiting, and block it, and 3) the line may collapse under the water pressure, blocking it. The physics of the 'A Brief History of Everything' story cited here requires that the air line be intact and open all the way to the surface, and that the diver's remains be forced out on the surface, which would be a lot more noticeable than whatever remains they found when they pulled the suit up.

Second, and much more common, is that the diver, in zero-visibility conditions (which are quite frequent in diving salvage), walks into a hole or off the side of a sunken ship. Since the diver is weighted down to keep him in place, he immediately starts to sink, and as he sinks, the pressure of the water on his body goes up. If his line-tender is doing his job, keeping slack out of the air line, safety line, telephone line, etc., the diver gets squeezed a little, the line tender pulls him back up, and he gets on with the job. If the line tender has been sloppy and there is a lot of slack, the diver is squeezed harder, and depending on the drop, is anywhere from injured to extruded into his helmet like toothpaste.

Since the helmet is an expensive piece of equipment, somebody gets to remove the diver's remains from it. Traditionally, this job falls to the errant line-tender, and a spoon is the legendary tool for doing so. Normally, line-tenders are either divers or diver apprentices, and have been squeezed themselves, so they have complete apprehension of the problem. And as part of their training, their trainers make sure they hear all about squeeze, and the stories get embellished and take on legendary aspects, so it's hard to separate out the details, such as who, when, where, how, and why, which are buried in brief naval accident reports.

Squeeze is almost entirely avoidable, and catastrophic incidents are sufficiently gristly to make the news, so they don't seem to be very common.

I don't know how much pressure it would take to extrude a human body like toothpaste, but several atmospheres at least, and figure about 35 feet of seawater depth per atmosphere. Properly, this Snopes entry should be answered by someone well-acquainted with the medical diving literature. Pondering gadgets like meat grinders and the mechanical advantage required for them leads me to suspect that extrusion of a diver into his helmet is a sea story, although injury and death by squeeze are very real.
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