A Comparison: Bullet, Blast and Forced-­Entry Rated Glass

The term “bullet proof” gets used pretty loosely. For example, one popular image frequently seen online is this “bullet proof bus stop,” which was set up as part of a marketing campaign by a well­-known manufacturer of laminates and adhesives:

bullet proof bus stop

The company loaded a bus ­stop poster case with $3 million; break the “bullet proof glass,” get the cash. This is a real picture of real money from a real promotional campaign—but that’s not real “bullet proof glass,” and the manufacturer never claimed it was. That campaign was promoting a “forced-entry” security coating.

Bullet Resistant Isn’t Burglar Proof?

This sort of confusion is very common—especially in a world where every iPhone case claims to be “bulletproof.” When you’re writing marketing copy, “bulletproof” is just a synonym for “tough.” But when you’re designing for real physical security, the distinctions between a bullet, a bomb blast, and a break-in are vital.
bulletproof glass bullet resistant barriers

Unfortunately, many suppliers and small­ time glaziers play fast and loose with these terms. And there is overlap here. For example, some bullet resistant materials are also forced­-entry rated, and many forced-entry solutions provide blast resistance. But this overlap is often counter intuitive: A car bomb is more powerful than a bullet, but most bullets will pop right through most blast resistant windows.

Here are the three terms you need to be able to immediately distinguish when considering security materials:

  1. Bullet Resistant
  2. Forced-­Entry Rated
  3. “Blast Resistant”

Bullet Resistant Glass Meets UL 752 Standards

Nothing is “bullet proof.” It may take hundreds of bullets, but every material eventually fails. That said, there are materials that are “bullet resistant”—and the only bullet resistant materials you should trust are those that have a UL rating.

UL 752 is the testing standard for “Bullet­ Resisting Equipment,” including bullet resistant acrylic, laminated glass, ballistic fiberglass, window framing members, doors, and so on. This standard stipulates the exact conditions under which materials must be tested, including number of shots fired, muzzle velocity, distance, angle, and the manner in which those tests are confirmed and verified. These tests must be performed by a third party NRTL (Nationally Recognized Testing Laboratory—a designation given by OSHA to companies that can perform product safety testing and certification).

The end result is a material with a specific UL rating indicating what number of which caliber bullets it can be expected to stop. If a material has not been tested by an NRTL and confirmed to meet a specific level of UL performance, then that material is not bullet resistant.

Forced­-Entry Rated Glass Meets UL 972 Standards

As the name indicates, forced­-entry rated glass is meant to slow, if not stop, attempted break-ins. The most common applications are showroom and display windows, as well as the exterior windows of government offices and financial institutions. The “detention glazing” used in jails and prisons may also be referred to as “forced-­entry rated” (although this type of glazing is usually tested against other standards, specifically ASTM F 1915, the “Standard Test Methods for Glazing for Detention Facilities”).

As with bullet resistant materials, the only truly “forced­-entry rated” window is one that meets a specific standard, UL 972 (the “Standard for Burglary Resisting Glazing Material”). These tests generally involve laying a sample of the glass on a horizontal platform, and then dropping a 5­pound steel ball on it from 8 feet (for “outdoor” applications), 10 feet (“indoor” applications), and 40 feet (simulating a “high ­energy impact”). Again, as with UL ­rated ballistic materials, this isn’t something where a manufacturer, distributor, or glazier can go out in their back lot with a bowling ball and “test” the glass. It only counts as “UL­rated” if the tests have been performed at a recognized NRTL facility.

While some ballistic materials (especially laminated products, like glass-­clad polycarbonate) also carry a forced-entry rating, it is highly unlikely that a window that’s simply forced­-entry rated will also stop bullets or a blast.

IMPORTANT: There are after market “security films” that can be applied to existing windows, and may impart meaningful forced-­entry protection. Few of these products are actually UL ­rated. Unfortunately, the aftermarket security film industry is still remarkably shady (especially its DIY segment). Treat these solutions very cautiously.

“Blast Resistance” is Tricky

“Blast resistant” is by far the most loosely used term in security architecture. There’s two reasons for this. First, there are many different types of blasts: different explosions created by different devices in different proximities have remarkably different effects. Second, blast rating standards are diverse and evolving: A material might be called “blast resistant” based on how it performs relative to ASTM F 1642 (a standard for “air blast loading”), ASTM F 1233 (a standard for “ballistics and physical attack”), ASTM F 1915 (the “detention glazing” standard), NFPA standards (which are set by the National Fire Protection Association and designed to prevent, rather than withstand, explosions), FM 6049 (the FM Global Group’s standard for buildings and lockers designed for explosives storage), various Department of Defense and military standards, and so on.

The most meaningful set of standards for blast ratings in the security field are the GSA/ISC Blast Resistance Criteria. This is the only standard recognized by the US GSA for government facilities. It’s a rated standard, reflecting how the material withstands a bomb blast. A material with a “1” rating on this scale provides very safe post-­blast conditions. A material rated “5” leads to highly hazardous conditions after a blast: Major structural damage, many dangerous projectiles created by failed building materials, and so on.

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