A fire door is used to stop the fire progressing through the building by reducing the fires ability to pass from room to room, as well as restricting the amount of oxygen that can feed a fire. Fire doors are usually either 30 minutes or 60 minutes fire doors that can contain a fire for a certain amount of time. Some fire doors are only made for keeping out fire but not smoke, and others are made to prevent smoke and fire from spreading.
Fire doors are often made out of a combination of different materials that are much more heat and fire resistant than wooden or glass doors. Intumescent seals are used around the borders of the door to prevent smoke and fire from passing through the gaps. They work by expanding due to the heat produced when a fire starts which therefore blocks any gap around the door that smoke or fire could pass through.
Although this is a broad overview, specific requirements for different situations mean that anyone who needs a fire door should always contact experts who can give specific advice. And check out Fire Door Safety Week for more information about the importance of properly installed and used fire doors.