by Vickie Lovell
The challenge of how to protect buildings from damage during high-wind events such as hurricanes and tropical storms is very complex, causing disagreement even among experts. There are several dynamics that must be considered as any specific recommendations are made about types of protection used to protect glass.
In lay terms, wind loading is the applied pressure against the filmed/glazed assembly during high winds. Those loads may exceed 150 to 200 or more pounds per square inch. Generally speaking, safety film on a typical residential window assembly is capable of withstanding high wind loads.
In a hurricane, however, wind pressures are high, but they are not constant. The pressure on the glazed opening may "push" the filmed assembly inward or outward. This has often been observed by building occupants in anecdotal reports as the windows appearing to "breath" as the hurricane passes over. Testing has shown that under specific conditions, safety film has performed well in this type of loading, also referred to as "cyclic loading."
The most difficult challenge in hurricanes and other storms is the problem of windborne debris. Since Hurricane Andrew occurred in 1992 in South Florida, millions of dollars have been earmarked for research by insurance companies, the National Association of Home Builders, the IWFA and others to determine what is a reasonable and appropriate level to protect glazed openings from windborne debris.
The research effort has not yet concluded. Field evidence and scientific research compiled to date is abundantly clear. There are too many variables to rely solely on any single form of hurricane protection and film, or any other protection method, should be factored into a total hurricane-preparedness package specific to each situation.
Two identical buildings with filmed glass will survive a hurricane differently as any of the aforementioned variables change. Safety film is simply one more variable.
Dade County, along with other Florida and Texas coastal counties, have adopted a test method that does not address this varying range of conditions. As a result, film and other products have to be tested to a "one-size-fits-all" type of testing for resistance to windborne debris. If the product does not meet the pass/fail criteria based on impact from a nine pound two-by-four at 50 feet per second, followed by 9,000 or 18,000 "inward" and "outward" cycles of "load," the product may not be marketed as "hurricane protection." Dade County does not take into account any other variables.
However, the SBCCI SSTD 1297 Test Standard for Determining Impact Resistance from Windborne Debris has been revised to reflect different levels of performance based on the wind speeds and missile weight.
More data is being developed resulting in further improvements to the test methods and a more reasonable (and affordable) range of products available to a building owner and its occupants. In the interim, safety film can provide an increased level of protection from windborne debris when compared to an unfilmed glazed opening. However, in the areas of highest exposure, safety film or any other single feature should not be relied upon exclusively for protection from hurricanes. The building occupants and owners must make informed and careful decisions in assessing the overall conditions and risk from damage to their building.
Vickie Lovell is president of InterCode Incorporated in Margate, FL, and serves as building code consultant to the Association of Industrial Metallized Coaters and Laminators.
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