Most fire doors are designed to be kept closed at all times. Some doors are designed to stay open under normal circumstances, and close automatically in the event of a fire. Whichever method is used, the door's movement should never be impaired by a doorstop or other obstacle. The intumescent and smoke-seal bounding of fire doors should be routinely checked, as should the action of the door closer and latch.
Some fire doors are held open by an electromagnet, which may be wired to a fire alarm system. If the power fails or the fire alarm is activated, the coil is de-energized, and the door closes. Wireless, battery operated fire door retainers can also be used to safely and legally hold fire doors open.
Rated fire doors are tested to withstand an ASTM E119 standard time-temperature curve for a specified period.There are 20, 30, 45, 60, and 90-minute-rated fire doors that are certified by an approved laboratory designated as a Nationally Recognized Testing Laboratory (NRTL, e.g., Underwriters Laboratories). The certification only applies if all parts of the installation are correctly specified and installed. For example, fitting the wrong kind of glazing may severely reduce the door's fire resistance period.