The Importance of Engineering Judgments for Perimeter Fire-Containment Systems

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Architects and construction professionals need to know the local code requirements, and their specifications must meet those requirements. Key to achieving this is understanding the fire-performance analysis reports provided by various manufacturers.

There are specific codes and standards that are relevant to perimeter fire-containment systems. It is important to understand these requirements when designing perimeter fire-containment systems and seeking and evaluating EJs.

The 2018 IBC, Section 715.4: Exterior Curtain Wall/Floor Intersection states that, where fire resistance-rated floor or floor/ceiling assemblies are required, voids created at the intersection of the exterior curtain-wall assemblies and such floor assemblies shall be sealed with an approved system to prevent the interior spread of fire. Such systems shall be securely installed and tested in accordance with ASTM E2307 to provide an F rating for a time period not less than the fire- resistance rating of the floor assembly. Although local codes may vary, generally fire-resistance-rated floor/ceiling assemblies are required in construction types I-A, I-B, II-A, III-A, and V-A. It is important to note that even when the floor/ceiling assembly is not required to be fire-resistance rated, Section 715.4.1 still requires that the joint be sealed with an approved material or system—typically mineral wool safing insulation—to prevent or slow the interior spread of fire and hot gases between stories.

This section of the code sets forth the two principles that form the basis of effective perimeter fire-containment systems, and the criteria by which any non-tested and listed system shall be judged: that the void between the curtain wall and floor slab is properly sealed, and that the firestopping system achieves a fire rating at least as high as the rated floor. Now we will take a look at the test standards used to evaluate perimeter fire-containment systems.

ASTM Test Standards

Section 715.4 of the 2015 IBC requires that only approved perimeter fire-containment systems be used. Such systems are specifically designed and constructed to protect the perimeter of an aluminum-framed curtain wall in accordance with ASTM E2307 and the IBC. However, the IBC recognizes that every building differs in its design details, and so EJs may be required to help the project team adjust the design for the containment system to function as needed for the specific site.

Perimeter fire-containment systems are tested differently than other rated construction. ASTM E2307: Standard Test Method for Determining Fire Resistance of Perimeter Fire Barriers Using Intermediate-Scale, Multistory Test Apparatus (ISMA) is the standard designed to test and measure how well a perimeter fire-barrier system can maintain a seal and prevent interior fire from spreading as the exterior wall assembly deflects and deforms when exposed to fire. The goal is to determine how long the perimeter fire barrier will prevent the flame from penetrating through the opening between the wall assembly and the floor assembly.

The ISMA structure is a two-story furnace that subjects a perimeter fire-barrier system to fire exposure from two sides at once. It is designed to simulate a building fire in which the fire causes the windows to break, allowing the flames to escape the room of origin and impinge directly on the exterior of the curtain wall. The test focuses on the joint, which is protected by the perimeter fire-barrier system. ASTM E2307 exposes the joint from the room of origin, and the exterior wall to fire from both interior and exterior as the fire plume exits the room through a window opening.

The fire originates on the first floor, or “burner room.” A second floor is located directly above the burner and is called the observation room. An interior burner is used to start a fire in the first floor room. Soon the room fills with flame and hot gasses. Approximately 5 minutes later, the exterior burner is ignited to simulate glass breakage on the first floor, allowing for fire exposure on the outside of the building. When the vision glass on the first floor breaks, flames and hot gasses spread up the exterior face of the exterior wall, while fire and heat attach the underside of the interior joint between the floor slab and perimeter curtain wall. The objective is to prevent flames and hot gasses from entering into the room above via the interior joint. If the fire breaks through the interior joint and fire is allowed to spread to the upper story (observation room) during the test, the system will have failed to provide a fire barrier.

Although the ISMA structure cannot represent a real-life situation—the floors are approximately 7 feet tall, for example—the test does provide a reasonable expectation of how the system will perform in an actual fire.

Tested systems receive two ratings: The “F” rating is the time in hours that a firestop system will prevent passage of flames through an opening.

Although not a pass/fail criteria, the “T” rating is recorded and listed on the tested design and represents the time period, that the firestop system limits the maximum temperature rise to 325 degrees Fahrenheit (163 degrees Celsius) above its initial temperature on the non-fire side. The ratings are established for the entire assembly, including the floor, safing joint, and exterior wall system, rather than just the safing joint alone. It should be noted that the F rating performance of the safing joint is what is required in the codes. The insulation rating is comparable to the T rating.

The UL testing laboratory provides two alternative ratings. The integrity rating is comparable to the F rating, but it reflects total compartmentation evaluating the performance of both the interior joint and the ability of the system to prevent the exterior spread of fire through the vision glass openings in the curtain wall above the perimeter fire-barrier system.

The Role of the International Firestop Council (IFC)

The International Firestop Council (IFC) is a non-profit association of manufacturers and users of fire-protective materials and systems. The organization’s mission is “to promote the technology of fire containment in modern building construction through research, education programs, and the development of safety standards and code provisions.” The IFC has developed guidelines to help design professionals, construction, professionals, building inspectors and officials, and firestop contractors evaluate and use EJs.


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Originally published in Architectural Record