When I worked loading the 747 freighter it often crossed my mind about being shut in as the main holds are quite long and it is easy to be completely hidden from where the hold door controls are situated on the fuesalage.
I always used to check the instruction on the inside of the hold doors for the opening instructions in case someone shut the door. That way I would have unlocked or opened the door and the crew would see a door unlocked warning and would have to return to the stand.
In hold 5, the bulk hold in the rear of the 747 the door is a very simple plug door that opens inwards and has a big lever on the inside. I used to close it from the inside during delays in windy cold weather. Even if you can't get out you atill have switches for lights, fans and heating controls on the inside, plus crew intercomms so you'd have to be very unlucky to not attract attention.
