fire door hinges

Mine aren't. They have one at top and bottom and one in the middle.

Jonathan

It has three hinges because it is heavy not particularly because it is a fire door. There are two at the top close together are to resist weight of the door. (Under tension) The bottom one is under compression.

Building regs (generally) require three hinges - partly to take the weight of the door, but primarily to help it resist warping during a fire. (For FD30 doors you may in some circumstances be able to get away with only two).

The traditional positioning of them is with the centre hinge mid span between the others. The layout you describe does seem common in hospitals etc. Perhaps a reflection of the fact that they will get lots of stress load on the top hinge every time someone pushed a bed etc into them.

The hinges themselves also need to be fire rated.

I have not seen a fire door with a hinge in the centre, as you say a lot of industrial and heavy doors seem to have them close at the top even though nothing is going to be pushed through them.

I would have thought that a centre hinge would best resist warping