Since we were in elementary school, public fire education programs informed us that closed doors are better than open doors in protecting firefighters from fire and from the products of combustion. Since we were in Firefighter I class, we have known that some doors are listed as fire-rated and need to be kept closed (or held open by a smoke-operated door holder) and that other doors are not fire-rated.

The standard to which fire-rated door and frame assemblies are tested is National Fire Protection Association (NFPA) Station 252, Standard Methods of Fire Tests of Door Assemblies, 2012 edition (also referenced as UL 10B and formerly as ASTM E152 or ASTM E2074). The door and frame assemblies are rated according to the length of time they can withstand the furnace test within the test parameters. The fire door ratings under NFPA 252 (2012 edition) are 20 minutes, 30 minutes, ¾ hour, 1 hour, 1½ hours, and 3 hours. Doors are also rated in hourly increments over three hours, but these ratings are not often used because of their cost. See NFPA 252 Chapter 8 and Section 8.1.3.1 for detailed information on the test and ratings.