All commercial properties must be inspected annually by the National Fire Protection Association. The underwriters laboratory agency decides whether any specific door model reaches the fire resistance ratings acceptable. The fire ratings for doors are based on time.
GH's metal doors (both single and double doors) ratings consist of 20 minutes, 45 minutes, 90 minutes or a 3-hour rating. GH's fire rated wood doors come with three options: 20, 45 and 90 minute ratings.
These time-based tests are based on the timed exposure of flames the door and assembly can handle; examining the hardware, wall and door assembly as written in the building code standards. The doors are put into a large furnace to properly test the door against its specific rating.