Since this is a forum and not a chat room, please give people time to respond to your queries. I don't know the answer off hand, but if another member sees your post and knows the answer, they will post it.
Please be patient and thank you for your co-operation.
>>When jack and rose go down to the boiler room which staircase do they use??<<
They don't. They use go in by way of a ladder through an opening in what looks like a fan room. Don't take that as representative of how the ship was actually laid out. There were ladders/stairs that would have ultimately led up to E-deck if my read of the plans is correct. While a ladder in an escape trunk is not outside of the realm of possibility...you see this all the time on warships for example...there would be no reason for any such to open up into a fan room.