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Actually a similar process is employed in submarine escape hoods 
(vests). The hoods are constructed somewhat like a horse-collar BC with 
a hood canopy (with a flexible plastic viewport) covering the neck 
opening in which your head fits. The lower opening of the hood is open 
to sea. Kind of like having your head in a bucket surrounded by an 
inner tube! The overpressure vents on the buoyancy chamber exhaust into 
the hood region. The operational scenario is something like this: the 
escapee enters the escape trunk and closes the lower hatch. He floods 
the chamber to a specific level; hooks an AIR hose to the escape vest 
and inflates it; and pressurizes the chamber to ambient pressure 
keeping the vest inflated (regardless of whether the ears clear or 
not). When the chamber is at ambient pressure, the upper hatch opens 
and the escapee unhooks the hose, ducks under the little cofferdam his 
head is behind, and ho ho ho and away he goes. On Mr. toad's wild ride 
up the air in the buoyancy chamber expands through the overpressure 
vent valves into the hood allowing the escapee to breath on the way up. 
He may or may not be bent at the surface depending on the depth of 
escape and bottom time at submerged pressure. True, true, true! But 
with today's ivory tower desk jockeys designing submarine hardware the 
latest mod may include an inflatable Bayliner with Chrysler outboard!

This process has been demonstrated deeper than 400 ft on air. Maybe 
these hoods shound be required for Deep Air courses, or for deep 
technical dives in general. 

Just having a little fun,
Doug Chapman

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