bulkhead

[Captain Smollett]

I can quite easily see a blocked companionway.

 A fire in the galley which formost boats is right AT the companionway would do it bigtime!!

Just to clarify my comment, I was talking about a sea hood preventing physical blocking from above like marujo_sortudo described.

Fire of course is always a big danger; a malfunctioning locking mechanism on the sliding hatch could prevent its opening as well.  Other conceivable causes could include deformation of the slides from a rollover (or other serious torquing) of the hull...that happened to Yves in the Indian Ocean, only he could not close his hatch, an equally big danger offshore.

Fore hatch = good for many reasons, but I was just talking about a way (with other specific advantages) to eliminate or at least reduce part of the problem.