Fire rated doors are used in buildings to prevent the passage of fire and smoke between two compartments or areas. They are used as a passive means of protecting people and property from fires. Model codes in the United States generally reference NFPA 80: Standard for Fire Doors and Other Opening Protectives when it comes to installation and maintenance of fire doors.
Doors and frames are given a fire-resistance rating after extensive testing by the Underwriters Laboratory in the United States, or another testing agency in other countries. Once tested, the door and frame receive a label that describes the amount of time the component is expected to provide protection when exposed to fire. When combined, all of the components of the door form an assembly that protects the opening. For this reason, all components of the door must include a rating label, including the door panel, the door frame, locksets, gaskets, hinges, and door protection plates. In other cases, the entire assembly (including all hardware) has a single rating.
A permanent label is attached to the door panel and the door frame, usually on the hinge side of both. Most other components have a UL symbol formed or stamped into the material to identify that they meet the UL requirements.
Local codes should be reviewed, but in general, rated doors must be self-closing and must have a positive latch. There are also limits to the size of glazing in the door, the width of gaps between door panels, the height of the door under-cut, and the size of air transfer grilles.
Chart of Door Ratings and UL Labels
As mentioned above, doors are labeling based on the amount of time (in hours or minutes) the door is expected to provide protection. Some very old doors may have a letter-rating, which corresponds to the time-based ratings. We include the letters in our chart below for reference, but the time-based ratings should be used on current projects.
|Hour Rating||Minute Rating||Letter Rating||Max. Glass Area|
|4 HR||240 MIN||—||—|
|3 HR||180 MIN||A||100 square inches per leaf|
|1 1/2 HR||90 MIN||B||100 square inches per leaf**|
|1 HR||60 MIN||—||1296 square inches per lite**|
|3/4 HR||45 MIN||C||1296 square inches per lite**|
|1/3 HR||20 MIN||—||1296 square inches per lite**|
** Limited to the maximum area tested
UL Labels D and E were used for exterior doors that are subject to fire hazards from the outside of the door; however, these are not longer used.
Doors may also have a Temperature-Rise Rating in number of degrees. This represents the expected surface temperature on the unexposed side of the door after 30 minutes of fire exposure. You will see this marked as 250°, 450°, or 650°. Glass included in the door must also meet the temperature rise requirements.
S-Label or "Smoke Rating"
Many codes require an S-Label for certain doors in some occupancies. For instance, corridor doors often require smoke protection to prevent smoke from leaking from or into an occupied space.
An S-label isn't exactly a "smoke rating". Rather, the S-label indicates the door meets the leakage tests that are part of UL 1784: Standard for Air Leakage Tests of Door Assemblies and Other Opening Protectives. However, smoke cannot pass through if air cannot leak through the door assembly. An S-label is usually achieved by installing UL approved gasketing.
Required Door Ratings Based on Partition Rating
The required door rating is based on the rating of the partition or barrier that the door is in. The table below provides an overview, but the building code should be referenced due to the complexity involved in determining the rating of the partition and the type of opening allowed. Table 716.5 in the International Building Code provides a detailed list of requirements. Local codes may vary.
|Type of Wall Assembly||Wall Rating||Minimum Door Rating|
|Fire Wall / Fire Barrier||4 HR||180 MIN|
|Fire Wall / Fire Barrier||3 HR||180 MIN|
|Fire Wall / Fire Barrier||2 HR||90 MIN|
|Fire Wall / Fire Barrier||1 1/2 HR||90 MIN|
|Fire Barrier Having a 1 HR FRR*||1 HR||60 MIN|
|Other Fire Barriers||1 HR||45 MIN|
|Fire Partitions (Corridor Walls)||1 HR||20 MIN|
|Fire Partitions (Corridor Walls)||30 MIN||20 MIN|
|Other Fire Partitions (Non-Corridor Walls)||1 HR||45 MIN|
|Other Fire Partitions (Non-Corridor Walls)||30 MIN||20 MIN|
|Exterior Walls||3 HR||90 MIN|
|Exterior Walls||2 HR||90 MIN|
|Exterior Walls||1 HR||45 MIN|
|Smoke Barriers||1 HR||20 MIN|
Fire Rated Door Field Modifications
Field modifications of a fire rated door require specific knowledge of the codes and should be performed by a person qualified to work on rated openings. NFPA 80 provides specific guidance on what can and cannot be done to a rated door. It is important to confirm that all new components have a label that matches the rating of the existing door and frame. In addition, the laboratory that initially approved the assembly must also approve the field modifications in writing per NFPA 80-2019 (5.1.5).
Fire Rated Door Annual Inspection
In the United States, NFPA 80-2019 (5.2.4) requires that fire rated doors be inspected each year to confirm that the door is in good condition and that all of the required components work as required. The building owner is responsible for having the inspections done by qualified person and for maintaining proper records of the inspections.
Refer to the codes applicable to your specific jurisdiction for label or rating requirements.