There are different types of fire doors, ranging from the length of fire resistance offered, typically 30 or 60 minutes, to the materials used to construct them. Fire doors classified as FD30 and FD60 identify the length of time a particular door can resist the spread of fire.
Types of fire doors can be made from fire resistant glass, timber, minimum 44mm thickness, or steel.
The door itself is usually made from a solid timber frame, but they can sometimes be covered again in fire-resistant glass. This glass should be able to withstand exposure to the heat condition in a fire test for at least 60 minutes before it reaches a temperature high enough to soften it.
Around the edges of the door will be the intumescent seal, which is designed to expand when temperatures reach beyond 200°C to seal the gaps between the door and frame.