Successful Perimeter Fire Containment

Shedding light on common misconceptions about PFC systems
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Sponsored by Owens Corning
Presented by Juliet Grable

Applicable Codes and ASTM Tests for PFC Systems

To understand common misconceptions about PFC systems, it is essential to first understand the code requirements and testing standards that are relevant to these systems.

Fire investigative reports have consistently shown that unprotected or improperly protected penetrations and joints have caused millions of dollars in property damage and contributed to the loss of life and injuries due to the uncontrolled migration of fire, smoke, and toxic gases. Consequently, the International Code Council (ICC), International Building Code (IBC), and most state and local codes clearly state the requirements for passive fire protection. The IBC includes fire testing and performance requirements for firestopping for penetrations and joints. These provisions can be found in Chapter 7: Fire and Smoke Protection.

Relevant Building Codes

Section 715.4: Exterior Curtain Wall/Floor Intersection of IBC 2018 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, fire-resistance-rated floor/ceiling assemblies are generally 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 code does contain an exception for situations where vision glass extends all the way to the finished floor level. In these cases, code allows the void created at the intersection of the exterior curtain wall and floor assembly to be sealed with an approved material to prevent the interior spread of fire. This material “must be securely installed and capable of preventing the passage of flame and hot gases sufficient to ignite cotton waste,” as tested by ASTM E119. The material must resist the fire for a time period that is equal to or greater than the fire-resistance rating of the floor assembly. We will discuss the “ASTM E119 exception” more thoroughly later in this course; however, it is important to note that taking advantage of this exception is not recommended.

First, although ASTM E119 is an important test for evaluating building elements, it only tests fire exposure on one side of the assembly. Second, at the time the exception was incorporated into this section of code, there existed no designs tested to ASTM E2307 that allowed for the extension of vision glass down to the floor line. This is no longer true.

To summarize, Section 715.4 sets forth the two principles that form the basis of effective PFC 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 with a system tested to ASTM E2307, 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 PFC systems.

ASTM Test Standards

Section 715.4 of the 2015 IBC requires that only approved PFC 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 engineering judgments may be required to help the project team adjust the design to ensure that the containment system will function as needed for the specific site.

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 that originates on one floor and 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 PFC system. ASTM E2307 exposes the joint to fire from the room of origin and exposes the exterior wall to fire from both the 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 room and functions as the observation room. An interior burner is used to start a fire in the first floor room. Soon the room fills with flames and hot gasses. Approximately 5 minutes later, the exterior burner is ignited to simulate fire exposure on the outside of the building. When the vision glass on the first floor breaks, flames and hot gasses spread up the face of the exterior wall and through the joint between the floor slab and perimeter curtain wall. The objective is to prevent flames and hot gasses from entering into the room above. If the fire breaks through the upper-story windows during the test, the system will have failed to compartmentalize the fire.

Tested systems receive two ratings: The F rating is the resistance to fire spread, in hours. It is a measure of the number of hours the assembly resists the propagation of fire to the unexposed side through the interior joint.

The T rating is not a pass/fail criteria per E2307 but is simply reported in the listing. This rating is a measure of the time period, in hours, 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 UL testing laboratory provides an alternative rating called the Integrity rating. It includes the F rating, but it also evaluates the passage of flame through openings in the curtain wall above the PFC system.

Recall that “leapfrog” describes the condition where a fire breaks the glass in the room of origin, allowing flames and hot gasses to escape outside the building and up the face of the curtain wall. There, the fire breaks through and reenters the building by means of the vision glass in the floor above. Although not a requirement of the building codes, this is still a critical area that should be considered for maximum protection and compartmentation of a fire.

Shown is an illustration of the ISMA Test Apparatus. The test begins with ignition of first-floor interior burners. The objective is to keep fire from spreading through the interior joint between floor and exterior curtain wall on the second floor.

ASTM E2874: Standard Test Method for Determining the Fire-Test Response Characteristics of a Building Spandrel-Panel Assembly Due to External Spread of Fire. Although the path of fire via the exterior curtain wall is not currently addressed by the IBC codes, a new ASTM test standard was developed in 2019 to address this fire risk. Sometimes called the “Leapfrog Standard,” ASTM E2874 can be used as total fire-containment method when evaluating buildings that are a higher risk, such as health-care facilities, hospitals, and retirement dwellings, where egress out of a burning structure could be delayed.

As the name implies, ASTM E2874 evaluates the fire performance of an exterior wall assembly, principally the building perimeter spandrel system, for its ability to prevent the spread of fire to the interior of a room one adjacent storey above via fire spread from the exterior of a building. The test sample includes the exterior wall spandrel panel assembly, fasteners, structural supports, and any glazed openings. The test itself simulates a post flashover fire exposure within a compartment that is venting to the exterior of the building and spreading to the floor above via the building’s exterior. The testing apparatus is modelled after the one prescribed in ASTM E2307. As with ASTM E2307, assemblies receive an F rating and T rating.

 

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Originally published in October 2020

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