Ballistic Threats

The ballistic threat is a projectile fired from a weapon, which results in the full or partial penetration of materials. The goal of a ballistic attack is to kill or incapacitate occupants or damage structures and equipment. Although in some parts of the world those weapons can include sophisticated artillery, for most facilities ballistic threats are most often bullets fired by handguns or rifles. In most design criteria, the severity of the threat is expressed in terms of the type of firearm and the bullet, and the level of protection is specified as how resistant the product in question is to the bullet’s effects.

There are several widely-used ballistic test methods that can be used to specify ballistic resistance of building elements. Each test method denotes specific testing criteria, including the ballistic threat in terms of a bullet type or size (e.g., 9 millimeters), the distance at which the test sample is placed, the number of samples, the testing temperature, and the material and location of the witness panel (a piece of material, e.g., aluminum foil, that is placed on the protected side of the sample for the purpose of determining whether fragments are produced during the ballistic test). The testing methods all take slightly different approaches, depending on the criteria, and the end users must select the test method most appropriate for their application.

The Ballistic Threat Severity Chart shows examples of threat severity levels defined in Underwriters Laboratories (UL) and National Institute of Justice (NIJ) criteria, related to specific weapons and ammunition.

Image courtesy of Ross Technology

The level of protection defined in each ballistic test method measures the degree of bullet penetration through the surface and also the presence and amount of “spall,” flecks, or shards of material from the protective side of the laminate that might break away on impact and become projectiles themselves. Most written specifications require “no spall,” which is a “high” level of protection.

For building products, widely used ballistic test methods include:

• UL 752: defines 10 levels (plus shotgun) of protection
• National Institute of Justice (NIJ) 0108.01: defines six levels
• SD-STD-01.01 Rev G (Amended) Certification Standard Forced Entry and Ballistic Resistance of Structural Systems: defines three levels (plus shotgun) of protection
• ASTM F1233: defines 10 levels (plus shotgun)

The relative ability of various materials to resist three representative types of ammunition, generally from a lower threat level (for example, .44 Mag bullets) to a higher (7.62 M2AP bullets), is indicated in the Ballistic Threat Resistance Table. The definition of what level of protection would be “realistic” in any building is relative and depends on the nature and level of the threat, budget, building’s mission, and many other factors. For the purpose of comparison, the chart indicates a typical range of threat levels for which products are commercially designed and available. (Although it is possible to provide building components that can provide protection against more powerful ballistic threats—for example, against incendiary or .50 caliber armor-piercing ammunition—these products are not widely available for commercial applications.)

Image courtesy of Ross Technology

Manufacturers offer a number of fenestration products that meet ballistic threats, with innovative component and system designs that will work well in almost all building configurations. These systems feature multiple glass layers to dissipate the bullet’s energy and layers of plastic or film to capture spall, in frames of steel, armor plate, or thick aluminum, with all gaps protected. It is important to remember, particularly with large caliber rifle rounds, that a significant reaction can be transferred to the rest of the building structure when the ballistic-resistant glazing functions as designed and stops the penetration of a projectile.