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As Total Security Solutions vice president Jim Richards explains, “There’s a lot of different products out there, all of them are fit for different applications,” and all are indiscriminately called “bullet proof glass” by most people. There are four types of bullet proof glass you’ll see in most pharmacies, banks, shops, or government buildings: bullet proof laminate, monolithic acrylic, polycarbonate, and glass-clad polycarbonate.
Bullet Proof Laminate
Bullet proof laminate glass is the traditional “bullet proof glass”, crafted from layers of glass and resin, similar to a stack of modern car windshields. This old-fashioned glass is no longer useful in a bullet resistant installation: It’s heavy, brittle, and cannot be readily cut, slotted, drilled, or otherwise integrated into a meaningful bullet resistant system. Experienced fabricators, like TSS, have the equipment and experience to build quality systems with laminated glass (although it typically takes an additional 6 to 8 weeks to build such systems).
By far, the most common “bullet proof glass”: a single piece of 1 1/4″ to 1 3/8″ solid plastic. Acrylic can be drilled, routed, cut, and slotted to seamlessly integrate with the mounting hardware and surrounding architecture in a quality bullet resistant system, or to build novel bullet resistant structures. Acrylic passes light almost perfectly, and since its rough cut edges can be flame-polished clear, it lends itself to the attractive, unobtrusive installations favored in most public buildings.
Bullet resistant systems relying on acrylic can be fabricated to UL-rated Level 1 or 2 bullet resistance. A Level 1 system can stop three jacketed 9mm bullets, while a Level 2 system can stop three shots from a .357 Magnum. To beef up to Level 3 security–capable of withstanding at least three rounds from a .44 Magnum–Total Security Solutions sandwiches 1″ of acrylic bullet proof glass between two sheets of polycarbonate. This keeps the excellent material qualities of the acrylic while adding a little of the bullet-grabbing capacity of the polycarbonate.
Polycarbonate and acrylic are very different beasts. Acrylic is hard, and polycarbonate comparatively soft. When used on it’s own in a bullet resistant system, polycarbonate is laminated in layers. Consequently, it has a noticeable tint, passing a bit less than 80 percent of available light, which can make for a gloomy interior.
But polycarbonate can offer Level 1 protection in just 3/4″, Level 2 at 1″, and Level 3 at 1 1/4″. Polycarbonate is great for exterior windows because of its resistance to forced entry: a sheet of polycarbonate will take an hour of beating with a sledgehammer, where a comparable piece of acrylic might succumb in just minutes.
Polycarbonate is more challenging to fabricate into a smooth bullet resistant system, but the difference is clear when it stops a bullet: While hard acrylic fractures, sending the bullet ricocheting, Jim points out that “polycarb looks beautiful when it stops a bullet: since it’s soft, it sucks the bullet in like a catcher’s mitt.”
This is a high-tech spin on that old-school laminated bullet proof glass. For example, Level 3 glass-clad polycarbonate (capable of stopping three shots from a .44 Magnum) is a 3/8″ layer of glass, a thin coat of polyurethane, and another 3/8″ sheet of glass. These are then sandwiched between two more coats of polyurethane, and then 1/8″ outer caps of polycarbonate. The total thickness is just over an inch. Like traditional laminated glass, glass-clad polycarbonate is challenging to fabricate into acrylic-style seamless systems. And, like polycarbonate, it suffers from poor light-transmission. But glass-clad polycarbonate can be layered thicker and thicker to the highest-rated levels of bullet resistance, easily stopping a burst from an M16 or AK-47. This makes it a great choice for exterior applications: glass-clad polycarbonate holds up in high-traffic areas, weathers excellently, and carries ratings for forced entry, explosive blasts, and hurricane winds.