Fire-rated doors must be installed correctly in accordance with the manufacturer's instruction and include the specified ironmongery and other facilities which represent the doorset as originally tested as this is critical to the door's performance in the event of a fire. The British Woodworking Federation believes "third party certification is the only way to ensure that Fire Doors are manufactured consistently to protect lives and save property. Cutting corners can cost lives."
Fire doors can be made with a combination of timber, steel, gypsum, and aluminum, and the most widdely used ones are Steel Fire Door and Wood Fire Door. They can also have windows, which are made from borosilicate or ceramic glass (both of which offer a higher fire resistance than standard glass), and may contain an anti-shattering wire mesh.
To enhance their fire-stopping abilities, fire doors are flush with the frame. Any or all gaps are filled with silicone-based fire-resistant sealant. These are often accompanied by a keluar (exit) sign and an intumescent strip attached at the bottom of the door, which expands when exposed to heat to prevent smoke from seeping underneath.
http://www.firedoorfactory.com/fire-door/steel-fire-door/
