Successful Perimeter Fire Containment

Shedding light on common misconceptions about PFC systems

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Five Common Misconceptions about PFC systems

Now that you understand the critical design criteria for design and installation of PFC systems, let’s look at common misconceptions about PFC. These misconceptions relate to common design and installation errors as well as recent trends in zero-spandrel or all-vision glass assemblies and the increasing popularity of unitized curtain walls with back pans. Both of these create a unique and challenging firestopping condition that must be addressed.

Misconception #1: Mineral wool is mineral wool; any type and manufacturer of mineral wool can be used in PFC systems.

A common misconception is that all types of mineral wool provide the same level of fire-resistive characteristics. As long as you have the correct density and thickness of mineral wool, the PFC system will perform and provide the required level of fire protection. However, this is not true.

There is more to the manufacturing of mineral wool than simply melting rocks. In fact, mineral wool manufacturers have patented technology around the equipment that transforms molten lava material (slag and natural occurring rock) into fiber, as well as proprietary formulations in rock/slag and binder chemistries that produce specific performance attributes. For example, some mineral wool products are designed purely for thermal and moisture performance, while other formulations enhance the material’s acoustical attributes and are ideal for applications where sound attenuation is key. Still other chemistries are developed for industrial applications such as insulating ovens and kilns.

Although all mineral wool products are made of raw materials that make them noncombustible, one cannot assume that a product designed for sound control will provide the level of fire protection needed for a structural column subjected to rigorous fire conditions.

Similarly, an industrial 4-inch-thick, 4-pcf-density mineral wool insulation will not provide the same level of fire protection as curtain wall or safing insulation in a UL/Intertek tested and classified PFC system. The components of a PFC system must be able to withstand direct flame impingement and temperatures greater than 1,800 degrees Fahrenheit while maintaining their structural integrity. This underscores the importance of specifying PFC systems that utilize mineral wool that has been tested, verified, and marked by the independent third-party laboratories specific to ASTM E 2307.

THE IMPORTANCE OF THIRD-PARTY TESTING

Third-party independent testing is required for demonstrating that a system will provide the necessary 2- or 3-hour ratings for perimeter fire-containment (PFC) applications. These labs use ASTM E2307 to test systems and ensure that they block the path of fire at the interior safe-off void between a rated floor and nonrated exterior curtain wall.

Conformance to third-party quality-assurance programs allows mineral wool manufacturers to apply the UL/Intertek classification markings to their products. Manufacturers spend millions of dollars per year on this certification, and for good reason. By choosing certified products, the end user can feel confident that these products have been tested and proven to provide protection per ASTM E2307. They can also be assured that the products are continually scrutinized and monitored by the independent third-party labs to ensure their safety and quality.

In the past five years, an influx of prefabricated and pre-insulated curtain wall panels have entered the United States from other countries. These products contain mineral wool insulation—an essential element required for successful PFC—but they have never been tested to ASTM E2307 and thus do not meet our building codes. Such products pose a significantly higher risk of product or system failure in the event of a high-rise fire. In addition, there have been cases where panels containing uncertified mineral wool product were installed on a building but only discovered after the fact. The insulation had to be removed from the unitized curtain wall panels and re-insulated with a certified product, costing millions of dollars. This is a risk that can easily be avoided simply by requiring that UL/Intertek mineral wool insulation be specified and installed in PFC assemblies.

Now let’s look at the services provided by third-party entities such as UL and Intertek.

Pre-test visit: Third-party verification involves more than the tests themselves. In fact, before even running an E2307 PFC test at the testing facility, lab representatives will visit the mineral wool manufacturing plant and witness the production of the very material that will be tested in the full-scale test at their lab.

Testing: After the product is manufactured, UL/Intertek has the product sealed and marked as inspected, and it is shipped immediately to the lab for evaluation. The controlled samples are then placed in the ASTM E2307 test apparatus, and the fire test is conducted.

Listing: Once the materials or system have successfully passed the test, the labs write up a listing and publish the system in their fire-resistance directories. UL lists mineral wool curtain wall and safing insulation by manufacturer and name of the product, whereas Intertek lists the curtain wall and safing as “use only mineral wool bearing the Intertek Certified Product Label.” The label indicates that the product has specifically been evaluated per ASTM E2307.

Follow-up monitoring: Both UL/Intertek require that mineral wool insulation products be monitored for quality-control purposes under a follow-up program. The purpose of the follow-up service is to ensure that the products that are installed in PFC systems in buildings are identical to the ones that were evaluated and tested at the lab. To assure that the same product that was tested is consistently provided, the mineral wool manufacturer must follow strict guidelines in its manufacturing process, including raw material selection, formulation, and overall quality control. Both UL and Intertek perform unannounced audits of mineral wool manufacturing facilities during which they inspect both the process and products.

Misconception #2: The ASTM E119 exception, allowed in the IBC, can be used in lieu of a tested and listed system tested to ASTM E2307.

Some curtain wall manufacturers offer designs that feature either short spandrels or no spandrels at all (only vision glass). Until recently, these designs presented a special problem for firestopping. Section 715.4 of the IBC states that the void created between the rated floor assembly and nonrated exterior wall must be sealed with an approved system, tested to ASTM E2307, which remains securely in place for the time period equal to the fire-resistance rating of the floor assembly. As was mentioned earlier, an exception in this same code section addresses assemblies where vision glass extends to the finished floor level. This section allows the interior void to be sealed with an approved material tested to ASTM E119, which shows it is capable of staying in place and preventing fire to spread through the safe-off area.

At the time this exception was adopted into the code, there were no listed systems with either all vision glass or vision glass extending down to the floor level that had been tested to ASTM E2307. Today, there are.

Specifiers should always utilize a system that has been tested to ASTM E2307 since this test more closely represents the conditions of a real fire. Recall that ASTM E2307 exposes the assembly to fire on both sides at the same time for the 2- or 3-hour period of the fire test. In contrast, ASTM E119 exposes fire to only one side of the system and does not represent an expected fire scenario in a high-rise building.

Shown is the intermediate scale multistory test apparatus used in the ASTM E2307 fire-resistance test.

Notice the flame height attacking the exterior on The Windsor high-rise in Madrid, Spain, that was destroyed by fire in 2005.

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Originally published in October 2020

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