Safety Glass

Glass areas present a tempting appearance of weakness in any building security plan. Safety glass, although never perfect, can make these areas of apparent weakness stronger than many standard walls.

The goal of safety glass is not to “never” fail”, but to make failures harder to force and to fail safely when failure does occur. For example, one of the important functions of safety glass is to prevent shards of glass from becoming dangerous shrapnel when the glass eventually does fail.

Perfectly indestructible safety glass, if it is ever developed, will focus attackers attentions on defeating window frames and surrounding walls.

Safety glass should provide resistance against the following threats:

  • Bullets
  • Sledgehammer
  • Blowtorch
  • Drill
  • Sabre Saw
  • Explosive force
  • Hurricane force winds

Bullet Resistant Glass

Underwriters Laboratories publishes specifications for various levels of bullet-resistant glass as part of UL Standard 752:

Rating Test
Ammunition
Nominal
Bullet
Mass
Grain (g)
Minimum
Test
Bullet
Velocity
Ft/s (m/s)
Number
of Shots
Level 1 9 mm FMJ with lead core 124 (8.0) 1175 (358) 3
Level 2 .357 Magnum lead JSP 158 (10.2) 1250 (381) 3
Level 3 .44 Magnum lead SWC/GC 240 (15.6) 1350 (411) 3
Level 4 .30 caliber rifle lead core SP 180 (11.7) 2540 (774) 1
Level 5 7.62 mm rifle lead core FMJ, military ball 150 (9.7) 2750 (838) 1
Level 6 9 mm FMJ with lead core 124 (8.0) 1400 (427) 5
Level 7 5.56 mm rifle FMJ with lead core 55 (3.56) 3080 (939) 5
Level 8 7.62 mm rifle lead core FMJ, military ball 150 (9.7) 2750 (838) 5
Level 9 Armor-piercing 0.30 caliber FMJ 166 (10.8) 2715 (828) 1
Level 10 0.50 caliber FMJ, military ball 709.5 (45.9) 2810 (856) 1
Supplementary
shotgun
12-gauge rifle lead slug 437 (28.3) 1585 (483) 3
12-gauge 00 lead buckshot (12 pellets) 650 (42) 1200 (366) 3

 

The DoD Minimum Antiterrorism Standards for Buildings also provides some guidance.

It’s Not Really Glass

Safety glass is currently manufactured from a wide range of materials using a variety of processes. Safety “glass” might be a glass, polycarbonate, PVB (Poly Vinylbutyral), TPU (Thermoplastic Polyurethane), Ethylene Vinyl Acetate, or acrylic material. It may then be glazed, laminated, or clad to another material to benefit from the advantages of both materials. The acrylic products are generally less expensive than the polycarbonate and laminated glass products. The non-glass products are often coated to provide additional scratch resistance.

These complex composite products are sold under names like Armormax, Cyrolon, Lexan, Makroclear, and Tuffak.  Often the window-makers will attempt to hide exactly which safety glass product they use.  Refuse to do business with any company which avoids sharing product names and technical specifications.

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