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Terrorist attacks and glazing affects

Recent events such as the September 11 attacks and the Oklahoma City bombing have dramatically heightened the need for increased security at all high-risk buildings. According to a published study by the Glass Research and Testing Laboratory at Texas Tech University, the leading cause of injury in the Oklahoma City federal building bombing was flying glass. In fact, it was estimated that of the hundreds injured in the bomb blast, 80 percent suffered glass-related injuries. To compile their study, University researchers visited the Oklahoma City bombing site immediately following the disaster. During their inspection, the investigative team found glass strewn over an area encompassing six miles to the north of the Alfred P. Murrah Federal Building, one mile to the south, and one mile on either side in downtown Oklahoma City. Shards of glass were even found embedded in walls and inside the buildings surrounding the site.

Structural damage and broken glass were major contributors to death and injury for both the targeted buildings and the surrounding area in the 1995 bombing of the Murrah Federal Building in Oklahoma City.

The researchers’ key findings, however, came while investigating how different types of glass products behaved during the explosion. While most glazing systems used in the downtown area of Oklahoma City in close proximity to the detonated bomb were completely destroyed, laminated glass windows and doors made with a polyvinyl butyral (PVB) interlayer performed better than any other glass type found. Having the glass stay in the frame helped protect the surroundings from additional amounts of falling and flying broken glass.

During a bomb blast, laminated glass with a PVB interlayer helps to diminish the effects of the explosion by allowing the interlayer to stretch and in essence absorb some of the energy generated by the blast. If the glass breaks, the PVB plastic interlayer in laminated glass tends to hold the broken frag-ments in place helping to prevent glass-related injuries and damage. With the appropriate types of glass and installation in frames, laminated glass with a PVB interlayer helps protect the interior of the building from the blast wave effect. By retaining the building envelope, the blast wave does not enter the building and cause additional damage by hurling furniture, fixtures and collectibles around the interior environment—causing the majority of damage to a building’s interior after an explosion. Unfortunately, laminated glass with a PVB interlayer was used in less than three percent of doors and windows in the Oklahoma City area affected by the blast pressure.

Laminated glass consists of a tough protective PVB interlayer which is bonded between two pieces of glass under heat and pressure.

In their analysis, Texas Tech researchers concluded that damage to people and property in the Oklahoma City bombing could have been significantly reduced had laminated glass with a PVB interlayer been used exclusively in the commercial buildings surrounding the Murrah Federal Building. They also concluded that more emphasis should be placed on the design of a building’s non-structural elements, especially glazed windows and doors.

The Oklahoma City bombing and other terrorist acts have led laminated glass with a PVB interlayer to be used and specified for many high-security buildings—including the $185-million Eagleton Federal Building located in St. Louis, Missouri, and the Las Vegas Federal Courthouse in Las Vegas, Nevada. In addition to using laminated glass in these federal buildings, the General Services Administration (GSA) announced that laminated architectural glass is among the products it recommends to provide bomb blast protection in all new construction and major renovations of federal buildings under their control. In fact, laminated glass was listed as a preferred system for use in federal facilities, as noted in a recent GSA release to the glazing industry, outlining information it had recently provided to regional offices “for planning purposes.”