Part II: Guns and Glass Ratings

by Thom Zaremba, shareholder at Roetzel & Andress

Guns, guns and yes … more GUNS! Leading the world in gun ownership with an estimated 400 to 500 million civilian-owned firearms, America has more guns than people, averaging 1.5 guns per person! With that many guns out there, it’s important to understand something about the ballistic resistance standards used to rate glass.

In my last blog, we looked at the 11^th edition of UL 752. Today, we’re going to look at some of the changes that were made in its 12^th edition. However, before diving into that, we need to look at one of the significant ways that UL 752 differs from other standards.

Many standards are linear, meaning they provide two or more linear levels of testing. For example, the “safety glazing” standard ANSI Z97.1, like many others, has two increasingly severe tests. Class B tests glass using 150 foot-pounds of impact force, while Class A impacts the glass with 400 foot-pounds of force. Because the tests are linear, if glass is successfully tested to Class A, it will also pass Class B.

While a simple linear increase in foot-pounds of force is a pretty good way to test whether glass will break (or break safely) when struck by a human, the factors involved in determining whether glass will keep humans safe from bullets are different and a lot more complicated.

The 11^th edition of UL 752 is only partially linear. The 12^th edition is not linear at all. You may remember from my last blog that the 11^th edition of UL 752 has 10 different test levels. While levels one, two and three are linear, the rest are not.

In the 12^th edition, successfully testing to one level says nothing about the ability of that glass assembly to pass any other level. This is because the 12^th edition of UL 752 matches different impact forces with different types of guns and bullets. To do this, the 12^th edition begins by breaking the different types of “guns” down into three different categories. It then breaks each of those categories into subcategories.

The first UL 752 category is “handguns,” designated “UL-HG.” That is then broken into four subgroups, “A” through “D.” Each subgroup is a different type of handgun, each with a specific type of ammunition, weight, velocity and kinetic energy of striking force:

• UL-HG-A is a 9 mm Luger using a 124 grain, full metal jacket with a round nose profile (FMJRN), having a velocity of 1,305 feet per second and a kinetic energy of 467 foot-pounds of striking force;
• UL-HG-B is a .357 Magnum using a jacketed soft point (JSP) bullet;
• UL-HG-C is a 44 Magnum using a jacketed hollow point (JHP) bullet; and
• UL-HG-D is a 9 mm Luger using a high-velocity FMJRN bullet.

The second category is “rifles,” designated “UL-RF,” and it is broken down into 10 different subgroups from “A” through “J.” These 10 subgroups include a range of different rifles, from UL-RF-A, which is a .30-06 Springfield using a JSP, 180 grain bullet with a velocity of 2,700 feet per second and a kinetic energy of 2,922 foot-pounds of striking force, to UL-RF-J which is a .50 caliber using a 660 grain M33 Ball FMJ bullet with a velocity of 2,910 feet per second and a kinetic energy of 12,389 foot-pounds of striking force.

UL 752’s final category is “shotguns,” designated “UL-SG.” This category is further broken down into only two subgroups:

• UL-SG-A is a 12-gauge shotgun using a 1 ounce, 437.5 grain slug with a velocity of 1,200 feet per second and a kinetic energy of 1,398 foot-pounds of striking force; and
• UL-SG-B is also a 12-gauge shotgun, but one that uses a 00 buckshot, 12 pellets, 650-grain shells with a 1,200 feet per second velocity and a kinetic energy of 2,075 foot-pounds of striking force.

Now that we’ve looked at some basics of the two editions of UL 752, in next month’s blog, we’ll look at how the 12^th edition fine-tuned the ability of those using the standard to make an “apples to apples” comparison of ballistic resistant glass assemblies and some of the “safe break” or “spalling” provisions in its acceptance criteria. Don’t miss Part III of Guns and Glass Ratings!