Hurricanes cause a tremendous amount of collateral damage and risk lives every year. It’s extremely difficult to protect residential homes and commercial buildings when winds of up to 120mph blow water and flying debris all over the place. When a glazing system meets up with hurricane forces, there are several issues to be aware of. First, it’s important to note that windows applied with security film can stand up to high wind-loads in most cases. Unfortunately, wind pressure from hurricanes is not always constant. Therefore, a glazing system will face both a “pushing” and “pulling” pressurization. This causes tremendous strain on the framing system and often leads to failure. Once an opening is created, the wind pressure inside the structure can cause walls and roofs to collapse. Second, the most destructive force during a hurricane comes from wind-borne debris such as roofs, trees, doors, etc. These items, in effect, become dangerous missiles that destroy almost anything in its path.
In 1992, Hurricane Andrew swept through southern Florida and became the most destructive hurricane of all time in terms of money spent (approximately $30 billion). Afterwards, an investigation unveiled a multitude of problems with existing building construction. Weak building codes, cheap materials and poor construction compromised the structural integrity of many homes and offices. The findings centered on the separation of windows, doors and roofing materials during Andrew that turned into destructive flying objects. This debris would then shatter and break many glazing systems and doors. As mentioned previously, when windows and doors are broken, the excessive internal air pressure from the hurricane can destroy walls, ceilings and, ultimately, the structure itself. Thus, the Dade County Protocol’s primary goal was to protect residential homes and commercial buildings from wind-borne debris.
The test focuses on two areas of concern: 1) impact and 2) pressure. To measure impact performance, two 9 lb. 2 x 4’s are launched from an air cannon at a glazing system with a speed of 34 mph. A manufacturer looking to qualify must provide 3 window samples and survive impact to the center of the glazing system as well as the corner of the window. This is known as the large missile test. Any window, door or skylight located up to 30 feet from the ground must pass the large missile test under the new code.
Additionally, a second impact test using smaller projectiles (5/8” steel ball bearings) is conducted to simulate smaller debris, which is more likely to strike a structure above 30 feet. As with the large missile test, the supplier provides 3 samples, but this test includes 10 impacts to the center of the window, 10 along the edge, and 10 near the corner. All 3 samples must survive the smaller missile test to pass.
The glazing system then needs to pass a pressure test under the Dade County Protocol. A wind-load cyclic pressure test is conducted which tries to simulate actual hurricane forces using 9,000 variable wind cycles. To pass, the window must remain inside the frame and not have a crack longer than 5” or wider than 1/16”.
The Effect of the Dade County Protocol on Security Film
Security film is not an approved protection system under the Dade County Protocol, as it does not meet the standards under the large missile test. Unfortunately, too much weight is placed on the large missile impact test because it’s a relatively unlikely event during most hurricanes. In fact, a separate study conducted by Applied Research Associates in 1996 concluded, “the probabilities of large missile impacts on windows for a typical house is less than 5 percent…” The only good news for window film dealers is the Dade County code does not apply to existing buildings or homes - it only applies to new construction. Therefore, dealers can sell and install security film to consumers and position it as an effective glass mitigation “upgrade.” The challenge will be to overcome confusion in the marketplace as to which codes apply to what products, i.e. security film is not approved for new construction but allowable on existing dwellings, laminated glass is acceptable, etc.
Other Types of Windstorms
|© 2009-2014 Johnson Window Films, Inc. Carson, California USA|