Uses and requirements for fire barriers, smoke barriers, and smoke partitions
NFPA Journal®, May/June 2012
There is sometimes confusion between the different types of walls, or barriers, used in NFPA 101®, Life Safety Code®, and when those barriers are required. The code lists three kinds of barriers: fire barriers, which are addressed in Section 8.3; smoke partitions, addressed in Section 8.4; and smoke barriers, which are addressed in Section 8.5. (The occupancy chapter may alter the requirements of Chapter 8, making them either more or less stringent.) It is important to understand that these barriers have different uses and requirements, and that the code states which is needed and where it is required.
These are used for many purposes, including separating occupancies, isolating hazardous areas, creating a horizontal exit, enclosing an exit, or creating a shaft. These barriers have a fire-resistance rating in hours, specified by the code. Depending on the purpose, the fire resistance can be as little as half an hour, or it can be one hour, two hours, and, in some cases, even three hours. Any fire barrier must be complete both horizontally and vertically, the latter meaning that the wall extends from the floor slab through any suspended ceiling and is tight against the floor or roof above. As an option, the barrier can sometimes terminate at the bottom of an interstitial space if the space is designed with a rating equivalent to the fire barrier. All penetrations of the fire barrier must be sealed to maintain the barrier’s fire resistance, and all doors must be fire-protection-rated doors of the appropriate rating. Fire-protection-rated dampers are required in ducts that penetrate fire barriers with a fire resistance greater than one hour.
These are used to restrict the movement of smoke and usually have a fire-resistance rating specified in the code. In new health care occupancies, for example, the smoke barrier must have a one-hour fire-resistance rating. In existing health care occupancies, the requirement is reduced to a half-hour fire-resistance rating. Any penetrations of the smoke barrier must be sealed to maintain the fire resistance and to ensure that the barrier is relatively smoke-tight. The doors in the smoke barrier may or may not be required to be fire-protection-rated. Again, the code will specify whether such a rating is required. Duct penetrations of smoke barriers will generally require smoke dampers, which are technically called leakage-rated dampers and are operated by smoke detectors.
Smoke partitions are designed to limit the movement of smoke and are not as substantial as smoke barriers. Smoke partitions generally do not have a fire-resistance rating and may terminate at a ceiling. Walls enclosing a sprinkler-protected hazardous area can constitute smoke partitions. Similarly, the code says that a typical, lay-in acoustical tile ceiling with ducted HVAC can be considered as limiting the transfer of smoke. The doors do not have to be fire-protection-rated but they must be self-closing. No dampers are required in duct penetrations.
Where barriers serve multiple purposes, such as acting as both a fire barrier and a smoke barrier, they must comply with both sets of requirements. It is not uncommon in some buildings, such as hospitals, for the corridor wall to serve several different functions. Portions of the corridor wall may separate a hazardous area, another portion may separate an exit stair, and another portion may be a part of the smoke barrier. Careful review of the drawings for new construction or of surveys of existing buildings is important so that the barrier is constructed correctly for its intended purpose.
Chip Carson, P.E., is president of Carson Associates, Inc., a fire engineering and code consultancy.