Brian Reay pretended :
We have a secondary door so it isnt an issue but it was something I
thought of. The roller doors are quite hard to wind up by hand, at least
the double ones. Trying to (somehow) push one up so it winds must be all
but impossible. You could smash it open but that is true of any almost
door.

Mine is not difficult to manually crank, it is very low geared and
needs lots of turns to raise it.

The control system is DC 24v, the motor 240v. My plan for if the 24v
system fails, is to just power the motor directly off 240v, it internal
motor limits will still be in circuit.