There are six classes of fire doors recognized in the United States. Typically, you’d use Class A fire doors and Class B fire doors for commercial spaces.

What is a Class B fire door? Class B fire doors can resist fire for two hours. They resist both the spread of smoke and fire throughout the building. The specific door will tell you its exact time rating. Many building codes now refer only to the time rating of a fire door and not a classification, as classifications have changed over time. You will need to pair your time requirement with a specific door, and that may lead you to a Class A door, Class B door, or another door.

What are Class A Doors?

Class A fire doors offer longer protection than Class B doors. They may resist fire and smoke for three hours. Again, the specific door that you’re interested in should have a rating that tells you exactly how long it will last in the face of fire.

If you need to meet a certain timeframe to provide higher levels of fire safety in your building, professionals can help you select the right door. This is especially wise in manufacturing plants and other buildings with a higher-than-average risk of fire.

What are Class C Doors?

Class 3 fire doors will resist fire for one hour. Typically, Class C fire doors do not meet building code requirements for doors in stairwells. However, they are often used in rooms and corridors to provide a basic level of fire protection.

Class C doors may also be called “smoke doors.” These doors will not stand up well to direct flame but can resist some transfer of smoke. There is no guarantee that a Class C door meets NFPA requirements for smoke doors, despite their colloquial name.

What About Other Door Ratings?

There are lower classifications of fire doors, but Class C is often the lowest form of protection acceptable according to modern building codes. A door that resists fire for less than an hour may not be considered a “fire door” by some organizations.

What Door Rating is Required for a One-Hour Wall?

If you are required by code to have a door that withstands fire for one hour or that works as a one-hour wall, then you are looking for a Class C fire door. In a commercial context, these doors are often used as internal doors between rooms. Their added protection over Class D and lower doors help prevent the spread of smoke and fire from room to room.

Fire Class Isn’t Everything

The class of your fire door isn’t the only important thing. Fire-rated doors are also only as good as their proper operation and hardware. Quality hardware, especially closers and hinges, must be in good condition to keep the door working properly and resist fire. If your door does not close automatically or does not close fully, it will not offer the level of fire protection that you expect. The service life of a top-quality fire-rated door is between five and eight years. Your commercial door professional can tell you if your fire door is in good condition.


If you need more help with your fire-rated doors, our team is available to help in Walnut Creek, Concord, Hayward and beyond.