The salon to back deck opening doesn't have a door. Nor is there a door between the berthing area and the salon (stairs yes, door no)
This is not, strictly speaking, true. The Conception and her sister ship the Vision do have pocket doors at the top of the set of stairs leading from the dive deck to the salon. These doors are closed when the boats are docked and locked with nobody aboard. In over 15 trips on the Vision - most of them with Finstad's Worldwide Diving Adventures - I've never seen them closed at a mooring or during operations, even when the weather is really miserable.
The emergency egress from the bunk room comes up at the aft end of the salon, right where those always-open doors are. That exit is as close to being "outside" as you can get without needing to make it sealed enough to be on the weather deck. The primary entrance to the bunk room is at the forward end of the salon, to the starboard of the galley.
If the main deck of the boat were fully involved in flame, neither exit would allow for a safe egress from the vessel. I suppose you could call this a design flaw, but realistically you can't address every contingency. This boat clearly went from zero to fully involved in a time period that would be beyond all but the most extreme safety planner's expectations.
As I've pondered what would have made a difference - which I've spent a lot of time doing over the past few days given the number of nights I've spent in those bunks - I think about the only way you would have had a chance is if there were a way to get through the hull directly from the bunk room without going up to the main deck. That's a pretty impractical way to construct an emergency exit due to the sealing that would be required, but it would allow a direct exit in the event of a fire. Given it's a plywood hull without glass, even an axe might have made a difference, allowing them to create an opening and get outside, though that'd take a lot of time when there wasn't much to be had.
My money is on the lithium battery theory for how this fire would have started. It's the kind of ignition source that would be most likely to kick off when virtually no activity was going on aboard the vessel, and it gets hot enough fast enough to involve the whole boat as quickly as appears to have been the case.
Could be something else, of course, but that seems the most likely cause to me.
As a final note, I think the emergency exit that's there is really more useful in the event of a sinking event than a fire. If the boat is going down by the bow, the primary exit could be submerged and you head up through the aft one. In a fire it would be a real trick to get everyone out through that back exit with smoke and flame clouding the air.
-Ben
