Super Ancient/Alteran, soon-to-be-ascended beings.
Even backward 20th century human submarine designers know that a DSRV attached to a submarine, with both the submarine door and the DSRV door open, can lose structural integrity, including when the submarine door is stuck open, and thus no "safety mechanism" to only allow the DSRV door to close when someone is in it would EVER be entertained -- at least not by backward non-soon-to-be-ascended 20th century submarine designers.
And hell, the Titanic had closeable transverse bulkheads (albeit, not designed very well, obviously), yet the Ancients figured they weren't necessary.
Regardless of anything said, I still think the design of the Destiny, with respect to keeping air inside, is complete ass.
Any safety mechanism on an airlock would keep a door closed, not open.