I want to have an electric door latch for the top and bottom of the "door" to the entrance of the layout since there will be tracks going across the door.  I thought of using automatic electric door locks, but decided against them because they are in the "locked" position if there is no power (the ones I could find anyways). 

I want a door lock/latch that engages when the power is ON.  This way, if there is a power failure, the door automatically will be unlocked without needing to worry about finding an emergency override.  This is of particular importance, since if there is a fire and the power is disabled because of the fire, seconds count!

So what would you recommend using so that the door "locks" when the power is ON, and unlocks when the power is off. 

During an operating session, anyone wanting to enter or exit the layout room, will press a pushbutton, which will disconnect power for 5 seconds to the door locks allowing the door to be open. At the same time, power within 18" of the tracks will be disconnected as well as long as the door lock is in the unlock position, or if the door is open. 
If there is a train that is either on the tracks on the door, or is closely approaching the door (within 18"), the door lock will not allow power to be disconnected to the locks so no one can open the door.  There will be emergency override switches to cut power, but the normal state would be if the track is occupied, no one will be able to open the door.  There will be a Green ,Yellow, and Red Light indicating whether the tracks are occupied, about to occupied or clear.

But for all of this to work, I need to find a solenoid that will strong enough to hold the door in position when power is ON, and disengage when the power is off.  So if anyone knows of such an item, I would appreciate it so I can finish this project.  Thanks!

Ken L .