- 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.
These tests are typically conducted by an independent third-party testing agency, such as UL
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.
Proper installation of a fire-rated wall assembly is very important. Good construction practices—executed in accordance with the manufacturer’s recommendations and the fire-rated assembly’s requirements—are crucial for ensuring that the assembly built in the field matches the performance of the sample tested. For these assemblies to block the passage of flames, smoke, and toxic gases through wall joints and penetrations, however, passive firestops are required.
At wall perimeter joints, or wherever openings are made through fire-rated wall assemblies, it is necessary to seal off these openings with firestop materials. There are four primary types of joints or penetrations associated with fire-rated wall assemblies to which tested firestopping systems may be applied:
- Joints between fire-rated construction components, such as wall-to-wall, wall-to-floor, and wall-to-ceiling
- Floor perimeters—the edge of a slab foundation or curtainwalls
- Penetrations made through walls for mechanical, electrical, structural, security, piping, or wiring applications
- Electrical boxes where combined openings exceed 100 sq in. in 100 sq ft of wall.
Traditional firestopping materials used to seal these openings include: sealants, intumescent materials, sprays, mechanical devices, and foam blocks or pillows. It is important to note before selecting firestopping materials that there is not one universal product that will work for every firestopping application. It is also wise to select products that have been appropriately tested by an accredited third-party agency to meet applicable fire safety standards. The most effective of these materials are sealants, intumescent materials, and the newer technology of integrated firestop systems.
Sealants are the most commonly used group of firestop products due to their versatility. Caulk, for instance, can have various uses on construction projects, such as sealing penetrations and construction joints. These products are available in various forms and chemical formulations. Firestop sealants in caulk, self-leveling, and spray grade are readily available in silicone, latex, and solvent-based products. They often require the addition of a backing material in the system for support. Often, the effectiveness of their application is governed by the ambient temperature of the space, and in unheated spaces during construction, this could be a problem. In addition, any overlapping work from other subcontractors, such as previously installed mechanical ductwork, piping, and so on, can interfere with the sealants’ application and inspection.
Intumescent materials are firestop products that expand in volume when exposed to heat or flames exceeding a specified temperature. They are one of the primary groups of products used in applications where one of the assembly components will deteriorate or burn away during fire exposure or where surfaces are uneven and a tight fit is not possible. The expansion of the material closes the void that is created when the item melts or burns away, thus maintaining the integrity of the fire-rated assembly. Intumescent firestop materials come in various forms, from caulks to metallic collars with intumescent strip linings, with each product being designed for a specific purpose.
Integrated firestop systems
The integration of intumescent firestop materials onto steel framing members is one of the most recent high-performance firestop innovations. In many of today’s commercial and institutional projects, architects and specifiers are now using steel tracks manufactured with a factory-metered dosage of intumescent material applied in a controlled environment to the track flanges. These products help architects specify product and assembly solutions for both hidden and exposed aesthetic conditions where fire, smoke, and sound resistance ratings are required. Single-source construction of wall assemblies and installation of joint protection can now be achieved by drywall contractors, thereby eliminating any trade overlap issues, common when installing traditional firestop materials. Track members having the intumescent material already integrated can provide up to 3 in. of movement and 3-hour fire-rated protection.
Integrated firestop products are easier to install than traditional firestop materials.
Contractors need only install the track member, which includes the intumescent tape, at the top, bottom, or sides of the wall. This eliminates the need to return and install sealants or caulking at a later time, therefore eliminating multiple labor and material operations.
Evaluating passive firestop systems
Like wall assemblies, the fire performance of passive firestop systems must be tested to industry standards. ASTM E1966: Standard Test Method for Fire-Resistive Joint Systems
, is one standard that covers sealants, coatings, and materials used in joints. ASTM E814: Standard Test Method for Fire Tests of Penetration Firestop Systems
is the complementary test to ASTM E119 that evaluates penetrations through a tested, fire-resistive (ASTM E119-tested) wall or floor assembly. The test involves a standard time-temperature curve and hose stream test and assigns ratings based on temperature rise (T) and flame occurrence (F) through the firestop-sealed penetration. An air leakage (L) rating can also be assigned. Air leakage simulates smoke movement through a penetration, measured in cubic feet per minute.
Fire-rated wall assemblies and passive firestop systems are crucial elements in the design of all commercial buildings. They help increase occupant safety, protect against massive property loss, and allow project teams to meet building code requirements. By following the guidelines for fire-rated wall assemblies and passive firestop systems, building and design professionals can produce interior building assemblies that provide the necessary fire protection to occupants as well as the structure. Combined with active fire protection methods and occupant education, these passive fire protection techniques provide a safer, more holistic strategy for protecting a building and its occupants.
Gregg Stahl is the director of product development at ClarkDietrich Building Systems, a manufacturer of steel framing and finishing products for the commercial construction industry. With more than 25 years of industry experience, he has served in multiple capacities at ClarkDietrich, including vice president of its subsidiary Vinyl Corp.