Conventional window glass was not designed to resist windblown debris, earthquakes, explosions, and terrorist attacks. Subject to such stresses, existing glass often breaks into lethal shards, endangering building occupants and passersby and causing property damage.Security window film can improve the ability of existing glass to mitigate the impact of explosive force and windblown debris. The film’s primary function is to hold glass in place. In some cases, the glass may shatter, but remain intact. The 1998 bombings at the embassies in Kenya and Tanzania injured over 5,000, many due to broken glass. Broken glass in the 1996 terrorist bombing of Khobar Towers at the U.S. Air Force base in Saudi Arabia resulted in over 330 injuries, 80 to 90 percent of which were caused by broken glass.Broken glass also results from natural disasters, such as the Northridge and Kobe earthquakes and Hurricane Andrew. Of the 25 largest insured catastrophes in the United States, 21 have occurred in the last decade. Global warming-related volatile weather may cause more large-scale, glass-related property damage, fatalities, and injuries.A hurricane can project an object through a window causing dagger-like glass shards to strike occupants. A shock wave from an explosion also causes glass to break into lethal projectiles. If the explosion is sufficient, glass may become atomized and breathing in atomized glass particles often results in death. Because X-rays cannot detect glass particles, physicians have difficulty finding glass inside the body.Typical window performance problems may include unacceptable air infiltration, poor insulating capability, inability to block solar heat, the transmission of ultraviolet radiation and noise, and vulnerability to electronic eavesdropping. Security enhancements to glass become more economically feasible if they do not impede, but actually improve, energy and other window performance capabilities. Existing glass can be replaced with laminated glass, two or more pieces of glass bonded by a polyvinyl butyral plastic interlayer. Compared to conventional glass, laminated glass can provide increased resistance to debris and seismic and explosive force. Security window film is an alternative to laminated glass. Security window film is an optically clear, tinted, or reflective layer of polyester film applied to the interior surface of existing glass. Typical film installations cover the visible portion of the surface of the glass all the way to the edge of the frame, but do not extend to the glass edge within the frame.Because security window film has the ability to stretch without tearing, it can absorb a significant degree of an explosion’s shock wave. If a shockwave shears the film, the shattered glass collapses attached to the security film with minimal damage and injuries. In multi-story buildings, security film may also prevent glass from falling to the street below.The optimum security window film not only provides increased protection from stress; it may reduce a building’s energy consumption by blocking solar heat. The cost of disruptions to building occupants in removing and replacing existing glass compared to applying security window film to existing glass also needs to be taken into account when comparing laminated glass and security film.Marty Watts is president and CEO at Houston-based V-Kool Inc. (www.v-kool-usa.com).
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