The escape route in a fire situation is frequently the route of everyday traffic, hence the fire doors must not impede the normal functioning of a building. As earlier noted, door retainers can be used to keep them legally open, although the doors should be regularly closed as part of their routine maintenance in order to prevent warping or other malfunctions that could compromise their integrity in a fire situation.
In serving to compartmentalise a building and/or preserve an escape route, the function of a fire door, when closed, is to provide resistance to smoke/fire for a minimum specified length of time. Typically, this is 20 minutes or 180 minutes (FD20 or FD180). It is possible to have steel fire doors offering up to 3 hours resistance but this level of protection is usually only a requirement in specific, high-risk environments. Thirty minutes should, in most situations, allow for the evacuation of premises and response of the emergency fire services. Your fire risk assessment should identify which level of fire resistance your fire doors should require.
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