The Role of Fire Barriers and Fire Doors in Compartmentation

What is a fire compartment?

A fire compartment is defined in NFPA 101®, Life Safety Code®, as “a space within a building that is enclosed by fire barriers on all sides, including the top and bottom.” If portions of the fire compartment comprise exterior walls, they do not need to be rated, unless they are required to be rated by another code or standard.

For example, if an exterior wall was part of a fire compartment and was only required to be rated by the building code based on its proximity to another structure, then that exterior wall would need to be rated. If that same exterior wall was not required to be rated by the building code, then it could still form part of the fire compartment without a rating. In order to fully understand compartmentation, it is also essential to understand what a fire barrier is.

What is a fire barrier?

A fire barrier is by definition “a continuous membrane or a membrane with discontinuities created by protected openings with a specified fire protection rating, where such membrane is designed and constructed with a specified fire resistance rating to limit the spread of fire.” As we see in the definition, a fire barrier gets a fire resistance rating while an opening protective gets a fire protection rating. For more information on what that means, see this blog.

This definition illustrates just how imperative opening protectives such as fire doors are to a fire barrier. They should not be thought of as two distinct features that exist independently. Instead, fire barriers and their opening protectives need to be thought of as a system. Incorrect opening protection can lead to the unexpected spreading of fire from one area to another.

The continuity of fire barriers is also extremely important. For horizontal continuity, there are three choices. The fire barrier must be continuous from:

• An outside wall to another outside wall
• A fire barrier to another fire barrier
• An outside wall to a fire barrier

The vertical continuity is equally important.
There are two options for vertical continuity.

The fire barrier must be continuous from:

• The floor through all concealed spaces, such as those found above a ceiling, to the bottom of the floor above.
• The floor to the bottom of the interstitial space as long as it has a fire resistance rating of not less than that of the fire barrier

Is fire compartmentation required?

The answer to this question is, “It depends.” There are areas where compartmentation is required by NFPA 101, such as exit stair enclosures or other vertical opening protection. Another common place you see fire compartmentation is through the use of a horizontal exit. The horizontal exit creates two separate fire compartments, and we rely on that fire barrier that serves as a horizontal exit to prevent the spread of fire from one side of the fire barrier to the other. Compartmentation is also used for hazardous area protection. Certain occupancies will require the use of fire compartments to separate areas that have a higher degree of hazard, such as boiler rooms or laundries, from the remainder of the floor.

Conclusion

I hope that the importance of keeping combustibles away from fire doors is now clear. Fire doors serve a purpose to provide opening protection in a fire barrier. That fire barrier is being utilized to minimize the spread of fire from one area of the building to another. Introducing combustibles on the fire door itself could impact the performance and result in the system (the fire barrier and fire door) failing.