Fire doors come equipped with a mechanism such as an electromagnet, designed to hold the door open during normal daily use. When a fire alarm is activated, the electromagnet shuts off and releases the doors.
If a fire is severe enough that a section of the building is burning, the fire doors will contain the fire for long enough time that occupants may exit and emergency vehicles can arrive on site. For this reason, fire doors are required to be self-closing and self-sealing. Tying or propping a fire door open is prohibited because this interferes with the effectiveness of the self-closing mechanism. Because a fire door is designed to prevent the spread of smoke from one part of a building to another, fire doors must be no more than a maximum of 3/4 inch off the ground. No carpet should be run beneath the doors.
Fire doors are placed at the entrances to stairwells, in entrances and exits to buildings and down long hallways. Fire doors are placed in fire-resistant walls are also measured for the amount of time that they can resist heat and flame from fires.
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