In many ways that "Saving lives at sea" footage supports my point. Looking around 34m57s you can see the D-class is completely level when upside down and is 90% above water. It would have contained a large air pocket along pretty well the whole internal length... and importantly the guy got out and lived.
Ok so still not a great experience but so so much better than that girl 3m under, no air and the buoyancy of her BA tightening its snagged straps on the downward facing cleat.
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