Hi, I've read your pages on fire doors but one thing concerns us. In both considering trying to adapt our current door with seals or buy a new one - am I right in understanding that in the event of a fire the seals expand to seal the gap completely? If so that means you cannot open the door? At exactly what temperatures does this happen? With only one exit the question is at what stage is it safer to be trapped inside (we are in a top floor 4 storey flat with only one exit door). Any advice to clarify that would be great.

Fire door seals only start swelling at around 120 degree Celsius. That temperature is a lot hotter than you could survive. Make sure you have smoke alarms that warn you early so that you escape before the temperatures rises dangerously.

The idea is that the strips expand to prevent hot gasses / flames from going any further than the door, so limiting damage. As harry says, by the time it does this you should have been long gone from the building.

I have seen a fire door after a fire. During the fire the strips did expand to stop hot gasses and flames getting past. One side of the door looked normal, the side where the fire was, the door looked like burnt toast