I always leave the ship to unload items in my car during a B2B and when allowed back on the ship I always go to my cabin to get rid of my carry on suitcase.
Although I've never experienced a closed fire door, when and if I do, I'll simply open it & proceed to my cabin.
On what ship did they have the doors closed? The Enchanted in March had their doors open on our deck, except for the Covid cabin side when we boarded (early).