Lack of oxygen?

I'm pretty sure there was a serious case of this a while ago with services Vancouver 34's fitted with special watertight bulkheads to the forcabin; seems a good idea for the safety of the boat but the occupants of the forecabins were nearly - or even actually, I'm not sure - suffocated.

It takes self discipline to open a ventilator into an already cold cabin but it's essential, against condensation as well - a possible answer is good ' 4 seasons ' sleeping bags if not cuddling up.
 
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