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Spend a few minutes searching the internet and you’ll find tons of images and videos showing hardcore tests performed on so-called bulletproof glass, forced-entry glass and blast-rated glass. No doubt, these materials get put through the wringer to prove their worth and satisfy the curious – what would happen if we fired a rocket-propelled grenade at a stack of bullet-resistant glass? The public seems eager to uncover the weaknesses of these materials, wondering if simple objects like diamonds, rocks or hammers will do some damage.
Unfortunately, all this “testing” and speculation can leave businesses looking for real physical security solutions in a state of confusion. But, understanding the capabilities and limitations of each material, and knowing what industry standards to trust make all the difference. And while some of these materials serve dual purposes, many only protect against bullets or break-ins or blasts, so understanding the differences is essential to determining the best solution for your threat profile.
Facts About Bulletproof Glass
Bulletproof glass is technically “bullet-resistant” and many forms don’t actually contain glass. Whether cast acrylic, polycarbonate or glass-clad polycarbonate suit your building security needs, you should only trust the integrity of materials with a UL 752 rating.
UL sets the standard for bullet-resistant materials, including acrylic, laminated glass, ballistic fiberglass, window framing members and doors. The UL 752 testing standard – performed only by a third-party Nationally Recognized Testing Laboratory (NRTL) – assigns the material a specific UL rating from Level 1 to 8, indicating how many of what caliber bullets it can stop. While Level 8 stands as the highest level of protection, the needs of most financial institutions, convenience stores and other businesses are met with Levels 1 to 3.
Bullet-resistant cast acrylic, available in UL Levels 1 and 2, is often used for indoor transaction windows and ballistic glass. Bullet-resistant polycarbonate, typically lighter than the other materials, comes in UL Levels 1 to 3. Its excellent optical clarity makes it well suited for exterior use. Ballistic glass-clad polycarbonate (GCP) can be manufactured to achieve UL Levels 1 to 8 performance. While heavier than the other materials, it’s ideal for exterior windows and also holds ratings for forced entry, explosive blasts and hurricane winds.
Even if the material is rated for hurricane winds, builders typically recommend additional features, such as reinforced structural posts, floor support and raised sills to improve performance and help the glass system withstand hurricane-force winds and water damage.
What is Forced-Entry-Rated Glass?
Forced-entry-rated glass involves a separate set of standards. Designed to delay, or preferably stop, an attempted break-in using sledge hammers, crowbars or similar objects, it’s often used in showroom and display windows, as well as external windows of government offices and financial institutions.
Forced-entry-rated glass must meet the UL 972 standard – the standard for burglary-resisting glazing material. To test for this rating, NRTL personnel typically lay the material on a horizontal platform and drop a five-pound steel ball from eight feet to test for outdoor applications, 10 feet for indoor applications and 40 feet for a high-impact simulation.
Remember, these materials delay or stop physical break-ins. A forced-entry-rated material will most likely not stop a bullet or blast, however, some bullet-resistant materials do carry a forced-entry rating. Also, be wary of after-market security films that can be applied to existing windows. While many of these products provide impact-resistance and UV-protection, they are usually not UL rated.
Blast-Resistance Ratings Vary by Circumstance
The variability of bomb blasts makes blast-resistant ratings less clear-cut. Different types of explosive devices cause different types of damage at varying proximities. As a result, blast-resistance ratings run the gamut and continue to evolve, making it more challenging to select the appropriate materials to meet your building security needs.
As the only standard recognized by the U.S. General Services Administration (GSA) for government facilities, the GSA/ISC Blast Resistant Criteria are most relevant to the security industry. The criteria rate materials on a scale of one to five based on how they withstand a bomb blast – one being most favorable and five being least favorable.
Other standards rate performance based on more specific circumstances. They include: ASTM F 1642 for air blast loading, ASTM F 1233 for ballistics and physical attack, ASTM F 1915 for detention facility glazing, National Fire Protection Association standards designed to prevent rather than withstand explosions, FM Global Group’s FM 6049 standard for buildings and lockers designed for explosives storage and more.