Better, cheaper screening of FRP building materials
FRP manufacturers who want to qualify FRP panels for use as exterior wall assemblies on buildings of any height must also meet the acceptance criteria of a battery of fire- and smoke-related performance tests.
Although the International Code Council’s (ICC, Washington, D.C.) International Building Code (IBC) was amended in 2009 with definitions that expressly permit the use of fiber-reinforced plastic (FRP) in residential and commercial construction (see “Architectural composites: Rising to new challenges,” under "Editor's Picks," at top right), FRP manufacturers who want to qualify FRP panels for use as exterior wall assemblies on buildings of any height must also meet the acceptance criteria of a battery of fire- and smoke-related performance tests.
The most challenging of these are the criteria associated with the National Fire Protection Assn.’s (Quincy, Mass.) NFPA 285 test method. It requires a fabricator to actually build a 15-ft wide by 25-ft high (4.6m by 7.6m) wall assembly with a window, and then subject that structure to a rigorous fire test. Compliance is both complex and expensive — the cost can run as high as $100,000.
Given that fact, testing dozens of different FRP formulations by the NFPA 285 method is out of the question. FRP fabricators, then, must prescreen candidate FRP laminate systems, using alternative tests. One method, ASTM E 85 (also known as the Tunnel Test), is already required in any case in which FRP materials are used in any interior or exterior application on a commercial building. It requires that a test specimen be installed in a horizontal (ceiling) position and then be exposed to a gas burner flame. The material must achieve an IBC Class A rating, measured as a flame spread index (FSI) of less than 25, and a smoke-developed index of less than 450. But the test is considered “intermediate” in scale because its specimen is smaller (24 ft long by 22 inches wide or 7.3m by 558.8 mm). However, a single test can cost several thousand dollars, so it, too, is not ideal for screening a large variety of FRP laminate formulations.
A more practical alternative for screening a variety of FRP materials is outlined in a paper written by Prof. Nicholas Dembsey, professor of Fire Protection Engineering, Worcester Polytechnic Institute (Worcester, Mass.), and several colleagues for the American Composites Manufacturers Assn. (Arlington, Va.). Dembsey proposes the use of ASTM E 1354. The Cone Calorimeter Test, as it is known, is a bench-scale test that requires only a 4-inch by 4-inch (101.6-mm by 101.6-mm) specimen and a relatively simple apparatus, involving a conical heater and a few other pieces of standard lab equipment. As the sample is heated, an oxygen analyzer measures the heat release rate of the material, an important parameter in fire hazard assessment. “The cone test is an immensely valuable screening tool for fabricators or materials suppliers to assess lots of materials quickly and relatively cheaply,” Dembsey contends. “You want to be sure what material will pass the 285 test so you only have to spend the big money once.”
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