A fire door is a sealed door between compartments, designed to prevent or slow the spread of fire, smoke and heat between those compartments. In a building, fire doors are generally fire-resistant sealed-frame doors, made of various materials and installed in fire-rated walls. Fire door requirements are set by the National Fire Protection Association. NFPA Standard 80 addresses fire door guidelines. It has been incorporated into most local building codes in the United States with little to no modification.
Fire ratings measure the amount of time that a door is able to contain the spread of fire, as tested according to NFPA guidelines. A door with a two-hour rating can be expected to resist combustion for two hours in the event of a fire. A fire door will typically have three-quarters of the rating of the surrounding wall. For example, a wall with a two-hour rating will usually contain doors with a 90-minute rating. The duration of a fire rating can range from 20 minutes to three hours, though 20-minute doors are designed to block smoke rather than flames. The rating requirements for each type of door and wall in a building are set by a fire marshal or by building codes.
All fire-rated doors and frames must be equipped with labels indicating they have met all testing requirements. The label must be provided by a certified testing agency, such as Underwriters Laboratory, and may be embossed or mechanically fastened. Labels must indicate the door's duration, such as 90 minutes, and may not be painted over or tampered with in any way.
Door and Frame Requirements
Wooden fire doors must have solid wood or mineral cores. Steel doors typically have honeycombed or insulated cores. The door should be prepped at the factory so there is no more than three-quarters of an inch of clearance between the bottom of the door and the finished floor. No holes larger than 1 inch in diameter may be drilled without voiding the fire rating. Pairs of doors must be equipped with an astragal, or overlapping seam or molding. Frames must be made from at least 16-gauge steel and should be prepped at the factory to receive hardware.
Fail-Safes and Fail-Secures
All fire doors must be self-closing and self-latching. This means that in the event of a fire, all of these doors will close and latch without manual intervention. This is accomplished through the use of a closer or spring hinge and a fire-rated lockset or exit device. Fire doors can never be held open with a door stop or any device other than a magnetic hold. The magnetic hold must be tied to the fire alarm so the door will close automatically during a fire. Electric locks used on fire doors must be fail-safe, never fail-secure -- that is, the doors will automatically unlock during a fire to save lives rather than remain locked to protect property.
Louvers and Windows
Louvers are permitted in fire doors only if they are labeled by a certified agency. The louvers must have fusible links so they close to prevent smoke from spreading. Glass windows are allowed but may not be used in combination with louvers. Doors with a 45-minute rating can have up to 1,296 square inches of glass; doors with 90-minute rating can have up to 100 square inches of glass. Three-hour-fire doors may not have glass windows.