Consumers searching for both security and the feeling of open space often ask for bulletproof glass windows, bomb proof windows or bulletproof home windows. In reality, this terminology is confusing and incorrect and deserves an important explanation. Contrary to popular myth, there’s no such thing as a bulletproof window. With the right caliber weapon and/or enough rounds, any window will eventually fail and allow bullets to penetrate. For this reason, experts commonly refer to such barriers as ballistic resistant or bullet resistant windows or ballistic windows.
Ballistic glass, sometimes also referred to as ‘bullet glass’, is commonly constructed of several layers or thicknesses of glass. The more layers and thicker the glass – the more stopping power the window possesses. Laminated glass sometimes incorporates special polycarbonates. These materials are the most protective ballistic resistant glazing available and are often used in bullet resistant doors as well.
Together these layers gradually erode the penetration speed of bullets when they strike ballistic glass windows. So unlike action scenes in movies, bullets don’t ricochet off bulletproof windows. They actually imbed in the glass and their kinetic energy is absorbed, slowing the projectile before it can penetrate the window.
Safety demands that the designer and end user thoroughly understand the suitability of the product for the application. In the protective design and security profession, architects and engineers equip facilities with the level of protection required by the threats likely to be encountered by the building and its occupants. Clearly, in military theaters of operation, ballistic resistant window requirements will be far more robust than civilians wanting bulletproof windows for homes. In fact, residential housing codes do not have requirements to install “bulletproof glass” windows. It is entirely optional.
Not surprisingly, bullet resistant windows meant for use at high value targets like chemical and petroleum facilities, government offices, embassies and military installations have very defined, incredibly robust requirements of ballistic and blast resistant protection.
Ballistic glass windows are typically rated for ballistic resistance, blast resistance, and resistance to forced entry. Rated bullet resistant windows are tested by several agencies, including the U.S. General Services Administration (GSA), U.S. Department of State Forced Entry/Ballistic Resistant standards and/or by Underwriters Laboratories (UL).
Created by Underwriters Laboratories, UL 752 ratings are the gold standard in measuring ballistic windows and range from 1 to 8 (from lowest to highest protection). For example, Level 1 glass can withstand fire from small caliber handguns and would be appropriate for what a consumer would call bulletproof windows for homes or residential bulletproof glass windows, but less effective for use in an embassy or military facility where the attackers would likely be armed with multiple round, high caliber weapons like an AK-47. This increased firepower requires far greater protection like that found in UL 752 Level 8 glass designed and tested to withstand multiple shots from a 7.62mm weapon.
The standard test methods for forced-entry resistance are set by ASTM International, formerly known as the American Society for Testing and Materials. ASTM’s methods are designed to determine the ability of various types of fenestrations to restrain, delay or frustrate forced entry. They are designed as a timed test using various heavy breaching tools applied to the window or door product in an attempt to gain entry.
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