Simple state machine's state table
I think you need to develop a state machine diagram similar to this (for how water is affected by stuff): -



Don't scrimp and scrape on "we don't need to worry about this or that" or "The supposition is that no one stays 10 seconds under the door" because you will not get a great answer because people will become disenchanted and think it is homework - just in case it is homework there is a tag you could have selected!!

You can still draw a state machine diagram and show the transistions you are discounting like the "supposition is that no one stays 10 seconds under the door" etc..

I'm sorry for sounding harsh or ultra critical but you do want this to be right, yeah?