Launch Slideshow

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Burn Notice

Burn Notice

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    Two-Hour-Rated, Metal-Stud-and-Gypsum Assembly

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    Two-Hour-Rated, Spray-Applied, Fire-Resistive Material Assembly

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    Two-Hour-Rated, Metal-Panel-and-Gypsum Assembly

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    Courtesy Underwriters Laboratories

    UL’s testing process involves placing test assemblies in a furnace and exposing one face to fire to determine the fire rating. In the case of glass assemblies (shown here), the fire is evident during the testing process.

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    Courtesy Underwriters Laboratories

    In the case of opaque assemblies, the testers must rely more on temperatures collected by thermocouples inside the furnace. After the test fire is extinguished, UL technicians can compile the temperature data, along with information such as roof-deck deformation (shown here) and material failure to help determine the rating (in hours) that each assembly receives.

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    Courtesy Underwriters Laboratories

    Column assembly after testing.

ANSI/UL 263 requires that the wall and partition assemblies being tested meet a minimum size of 100 square feet and a minimum length and width of 9 feet. UL builds the assembly and allows it to cure. Based on the requirements of the materials used, the test assembly may be conditioned until it reaches an equilibrium moisture content before being placed next to the test furnace. Inside the furnace, fire—intended to mimic conditions after the flashover or spontaneous ignition stage of a fire—is applied to one side of the test assembly. The furnace reaches increasing temperature benchmarks over the course of four hours—1,000 F at 5 minutes, 1,700 F at 60 minutes, 1,850 F at 120 minutes, and 2,000 F at 240 minutes, and the temperature of the fire and the assembly is recorded through a series of thermocouples inside the furnace. During the test, technicians look for flame passage through the assembly, temperature rise on the unexposed side, and whether the assembly can continue to support a load (if it’s a load-bearing assembly). An assembly’s rating is determined by one of several criteria: the time during the test when flames pass through; an overall temperature rise of 250 F (determined by the average temperature of all of thermocouples); a rise of 325 F at one of the thermocouples; or structural collapse.

After the fire-exposure test, technicians conduct what is known as the hose-stream test, which entails spraying the assembly with a high-pressure water hose to measure structural integrity. ANSI/UL 263 requires that the assembly withstand this final test without permitting water to project through. Also, if an assembly is not symmetrical—if one side is gypsum and the other masonry, for example—then two fire tests must be done, one from each side. The entire assembly is then given the lesser of the two performance ratings.

Innovations in fire-rated construction happen all the time. New fire-resisting materials come out, and existing products can be used in different ways to achieve different ratings. The versatility of the testing method leaves it up to the individual manufacturers to develop materials that meet industry needs and creates a situation where architects can motivate new systems that satisfy both codes and aesthetics.

UL publishes all of its testing results in its printed Fire Resistance Directory and makes it available online free of charge via the Online Certifications Directory and its Ultimate Fire Wizard database tool. “As time has gone on, the number of designs increases by about 10 percent per year,” Walke says. “Our directory has 1,750 individual designs now.” The Ultimate Fire Wizard allows architects to input details on a project through a series of pull-down menus and keyword searches, and then searches the UL database for matching designs.

Code in Bricks and Mortar

While the unitizing efforts of the ICC and tools such as UL’s Fire Wizard are making it easier for architects to understand the building codes as they apply to fire-resistive construction, and to find assemblies that comply with them, designing an efficient fire-protected building still requires a degree of subtlety. There are still many variations in the code from jurisdiction to jurisdiction, and even when the code is uniform it leaves much to interpretation. “There’s a table in the building code that mandates the type of fire-rated construction for use and size. It’s pretty plug-and-chug,” says Greg Miller, president of Code Consultants, a fire-protection engineering and life-safety consulting firm headquartered in St. Louis. “Then there are certain special options permitted under the code that you need to weigh thoroughly. If you don’t analyze the problems properly, it can mean millions of dollars.”

Code Consultants has made a practice out of understanding architects’ design goals and finding applicable construction options that meet the code from the start of the design process. While such consulting is commonplace in large projects, even small firms working on projects with tight budgets can benefit from the type of close analysis that such firms conduct. Since the code only mandates fire-performance characteristics, designers can search out unique material solutions. There is also tinkering that can be done to stay within the code, while reducing the cost of the construction.

Perhaps the most important benefit of closely understanding the code and how to meet it at an early stage in the design process is the possibility of getting preliminary approval of the concept and direction. “When we go to meet with officials, we want them to sign off so that we can proceed with confidence that we won’t get any surprises when we come in with permit drawings,” Smith says. “If there’s no delay for permitting, you can avoid adding more cost to the project.”

 

Note: This story has been updated since first publication to change "small-time architects working on minor buildings" to "small firms working on projects with tight budgets." When editing the article, we understood the first phrase to mean something perfectly straightforward, but we now appreciate how it left a negative impression. We are great believers in small firms' tremendous value to the profession and exceptional contributions to the built environment. Please accept our heartfelt apology.