Specifying passive firestop systems
Fire-rated wall assemblies and passive firestop systems are key elements to the design of all commercial buildings.
- Learn about recommendations for specific fire-rated wall assemblies and the industry testing they must endure to earn their ratings.
- Review examples of passive firestop systems.
- Understand best practices for the specification and installation of each.
With hundreds of lives often at stake and rebuild costs that can reach into the millions, it is no surprise that fire protection is one of the highest priorities of today’s commercial construction projects. While active fire protection solutions, such as fire extinguishers, smoke detectors, and sprinkler systems, may be the first to come to mind, it is crucial for project teams to give the same consideration to passive fire protection systems. Though passive fire protection systems are less visible than active fire protection systems, their function is equally as important.
Embedded in interior building assemblies, passive fire protection systems use fire-resistant materials to compartmentalize flames, smoke, and toxic gases at their point of origin. Compartmentation strategies involve the construction of barriers that divide a building into smaller units, which can confine a fire and allow the structure to avoid dependence on any singular fire safety plan. Most importantly, compartmentation limits the distance a fire can spread throughout the building and complements the sprinkler systems. This reduces property damage and affords occupants the needed time to safely evacuate the structure. Otherwise, the passive fire protection systems lie dormant and hidden from public view until a fire spurs them into action.
The most important area of concentration for passive fire protection systems are wall assemblies. All of today’s building codes require these assemblies to be tested by industry standards to evaluate their fire resistance.
Evaluating fire-rated wall assemblies
Passive fire protection strategies require a systematic approach—using an assembly of several different fire-resistant products that work together to impede the passage of flames, smoke, and toxic gases throughout a building. Such is the case with wall assemblies. For example, most exterior and interior commercial wall assemblies feature nonstructural cold-formed steel studs, fiberglass batt insulation, and gypsum wallboard—all materials with naturally high fire resistance. All three materials perform very well together in wall assemblies and are used in various combinations of thickness and numbers of layers to increase fire resistance. Walls (structural or nonstructural), floors, and ceilings can serve as fire barriers as long as they have a fire rating. These ratings are achieved through testing provided by industry standard ASTM E119: Standard Test Method for Fire Tests of Building Construction and Materials.
ASTM E119 evaluates the ability of a wall, floor, or ceiling assembly to contain fire, heat, smoke, and toxic gases for a quantified amount of time—usually measured in hours. The assembly is mounted to a specially constructed furnace, and gas burners are lit as thermocouples record temperatures and the flames mimic heat from an adjacent fire. Testing personnel observe the process through viewing windows in the furnace, recording the length of time before the system fails. A hose stream test follows to measure the assembly’s structural integrity, or ability to resist disintegration in the presence of fire and water. This test method uses a furnace-heating schedule, or timed increase of temperature, which brings the furnace up to 1,000 F in 5 minutes, to 1,700 F in 1 hour, and to 1,850 F in 2 hours. Assemblies must survive these temperatures to be successfully fire-rated by the standard.
Fire-rated wall assembly examples
Noncombustible wall assemblies must be constructed from fire-resistant materials and include only minor combustible components, such as paint and electrical outlets. All combinations of assemblies are tested to establish hourly fire ratings. Common variations of these types of assemblies are:
Typical 1-hour rated assembly; UL design V450; noncombustible, non-loadbearing
One layer of 5/8-in. Type X gypsum board is applied vertically to either side of minimum 3-5/8-in. steel drywall framing spaced on 24-in. centers. Gypsum board is fastened to the steel studs using #6X 1-in. long Type S bugle head steel screws at 8 in. on center perimeter and field. For horizontal applications—8 1/2 in. on center perimeter field. Vertical joints must be offset.
Typical 2-hour rated assembly; UL design V450; noncombustible, non-loadbearing
Two layers of 5/8-in. Type X gypsum board are applied horizontally to either side of minimum 1-5/8-in. steel drywall framings spaced on 24-in. centers. The base layer of gypsum board is fastened to the steel studs using #6X 1-in. long Type S bugle head steel screws spaced 16 in. on center perimeter and field. The same measurements apply to the face layer as well. Joints must be offset on the opposite sides of the wall and between layers.
Another important wall assembly demanding fire-resistance performance is the fire partition. Fire partitions are required between adjacent apartments or townhouses, and in some cases, they are required in commercial and institutional buildings.
A typical cavity-type area separation firewall assembly consists of two layers of 1 x 24-in. gypsum shaftliner panels inserted between floor and ceiling runners with steel H-studs installed between adjacent panels. A 3/4-in. air space must be maintained between steel components and adjacent framing. A 3-1/2-in. layer of fiberglass batt insulation in the adjacent wall cavity is also recommended.