What if a crew member opens Door A but forgets to disarm Door B, tottles off and goes home! Next morning catering van arrives at Door B and needs to open the door from the outside...he wasnt the idiot but he is the one who could be injured by the inflating slide, hence the need for warning signs!
Happened me, in Cork of all places. Ended up on my arse in the back of the catering truck.