{"id":2175,"date":"2018-04-18T16:13:18","date_gmt":"2018-04-18T20:13:18","guid":{"rendered":"https:\/\/info.glass.com\/?p=2175"},"modified":"2022-04-04T12:15:24","modified_gmt":"2022-04-04T16:15:24","slug":"bullet-resistant-glass","status":"publish","type":"post","link":"https:\/\/www.glass.com\/info\/bullet-resistant-glass\/","title":{"rendered":"The Use of Bulletproof Glass"},"content":{"rendered":"

In light of recent events the use (or lack thereof) of \u201cbulletproof\u201d glass in schools has come under fire. Let\u2019s start by addressing the fact that there is no such thing as bulletproof glass. What movies, the media, and pop culture commonly refer to as bulletproof glass<\/a> is in fact bullet-resistant glass<\/a>.<\/p>\n

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Bulletproof would indicate that no matter how many, and what kind of rounds are shot at the glass, it would remain intact. This is practically an impossible task. Given a large enough caliber gun, or enough round of ammunition, any glass will succumb to this violent force. This becomes especially true when you take into account the variety of rounds that are available. Explosive projectiles would destroy some \u201cbulletproof\u201d glass within a split second. The same concept holds true for hurricane resistant glass as well- given a strong enough storm with high winds<\/a> and flying debris, no glass could withstand prolonged damage.<\/p>\n

Hurricane resistant glass, which is closely related to bullet resistant<\/a> glass actually played a crucial factor in the recent school shooting in Parkland, FL. The shooter attempted to create a \u201csnipers nest\u201d but was unable to do so because after firing 16 rounds at a hurricane resistant window, it still did not break out, therefore thwarting his efforts at creating a vantage point to shoot from.<\/p>\n

The History of Bullet Resistant Glass<\/h2>\n

Let\u2019s start with a history lesson. Bullet resistant glass was actually first used during World War II in bunkers and on armored vehicles. But the process was crude- it involved layering numerous panels of tempered glass together with epoxy to create panels up to 4 inches thick. At this point, clarity was compromised and volume and weight made use prohibitive.<\/p>\n

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After World War II, bullet resistant glass evolved because people realized that it had applications beyond the battlefield such as in banks and other secured areas. Although acrylic (more on this below) had been around since the late 1800s, advancements in the manufacturing process turned it from a brittle plastic into a strong material which was, at the same time, relatively easy to shape and work with.<\/p>\n

Materials Used To Make Bullet Resistant Glass<\/h2>\n

So how is modern-day bullet resistant glass created? There are 3 types of materials used to make bulletproof glass that can possibly make up these panes.<\/p>\n

Acrylic<\/h3>\n

Acrylic is a type of extremely hard, clear plastic. Acrylic achieves bullet resistance through sheer thickness. Most bullet resistant polycarbonate is at least one inch thick and because of its density, is quite heavy. Because of its hardness, acrylic\u2019s defense is to deflect any projectile\u2019s energy and cause it to bounce off.<\/p>\n

Polycarbonate<\/a><\/h3>\n

Polycarbonate is also a type of plastic, but much softer and lighter- approximately 1\/3 the weight of acrylic. Because it is a softer material, polycarbonate\u2019s purpose is to absorb energy from projectiles and slow them down enough so that they do not pass through the material completely. Polycarbonate is layered, and many times the projectiles will become lodged within the layers. It is used in conjunction with glass to create glass clad polycarbonate which is also known as laminated glass.<\/p>\n

Laminated glass<\/a><\/h3>\n

This is often what people think of when they think of \u201cbulletproof\u201d glass like what\u2019s seen in movies. When impacted by a projectile, there will be an obvious point of impact where the outer layer of glass splinters. But hopefully the inner layers absorb the energy, stop the projectile, and don\u2019t let it pass through the other side.<\/p>\n

Laminated glass is basically a glass sandwich where there are 2 pieces of glass on either side with a soft layer of polycarbonate layered in the middle. You see this almost every day whether you know it or not- this is the same way that the windshield<\/a> in your vehicle is made. However, for bullet resistant purposes, layer upon layer of polycarbonate and glass is used to created the energy stopping power.<\/p>\n

With all the material types above, thickness is what matters most. The thicker the bullet-resistant glass, the further the projectile must travel, and the more energy will be lost.<\/p>\n

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Bullet-resistant glass struck by gunfire. Attribution: Vince Alongi, Bulletproof flickr<\/a><\/figcaption><\/figure>\n

Bulletproof Glass Testing and Specifications<\/h2>\n

Underwriters Laboratory (UL) has created standard security levels based on their testing. UL is the nation\u2019s top third-party consumer safety testing facility and test thousands of common household products. UL created UL752, the Standard of Safety for Bullet-Resistant Equipment. The chart below lists the levels and the forces they are able to withstand in order to pass UL\u2019s testing.<\/p>\n\n\n\n\n\n\n\n\n\n\n\n
Level<\/strong><\/td>\n\u00a0Ammunition Tested<\/strong><\/td>\nAmmunition Mass<\/strong><\/td>\nAmmunition Weight in Grams<\/strong><\/td>\nMinimum Velocity (Feet per Second)<\/strong><\/td>\nMaximum Velocity (Feet per Second)<\/strong><\/td>\nMeters per Second<\/strong><\/td>\nShots Withstood<\/strong><\/td>\n<\/tr>\n
1<\/td>\n9mm Full Metal Copper Jacket with Lead Core<\/td>\n124 grains<\/td>\n8.00<\/td>\n1,175<\/td>\n1,293<\/td>\n358<\/td>\n3<\/td>\n<\/tr>\n
2<\/td>\n.357 Magnum Jacketed Lead Soft Point<\/td>\n158 grains<\/td>\n10.20<\/td>\n1,250<\/td>\n1,375<\/td>\n385<\/td>\n3<\/td>\n<\/tr>\n
3<\/td>\n.44 Magnum Lead Semi-Wadcutter Gas Checked<\/td>\n240 grains<\/td>\n15.60<\/td>\n1,350<\/td>\n1,485<\/td>\n411<\/td>\n3<\/td>\n<\/tr>\n
4<\/td>\n.30 Caliber Rifle Lead Core Soft Point (.30-06 Caliber)<\/td>\n180 grains<\/td>\n11.70<\/td>\n2,540<\/td>\n2,794<\/td>\n774<\/td>\n1<\/td>\n<\/tr>\n
5<\/td>\n7.62mm Rifle Lead Core Full Metal Copper Jacket, Military Ball (.308 Caliber)<\/td>\n150 grains<\/td>\n9.70<\/td>\n2,750<\/td>\n3,025<\/td>\n838<\/td>\n1<\/td>\n<\/tr>\n
6<\/td>\n9mm Full Metal Copper Jacket with Lead Core<\/td>\n124 grains<\/td>\n8.00<\/td>\n1,400<\/td>\n1,540<\/td>\n427<\/td>\n5<\/td>\n<\/tr>\n
Level 7<\/td>\n5.56mm Rifle Full Metal Copper Jacket with Lead Core (.223 Caliber)<\/td>\n55 grains<\/td>\n3.56<\/td>\n3080<\/td>\n3388<\/td>\n939<\/td>\n5<\/td>\n<\/tr>\n
Level 8<\/td>\n7.62 Rifle Lead Core Full Metal Copper Jacket, Military Ball (.308 Caliber)<\/td>\n150 grains<\/td>\n9.70<\/td>\n2750<\/td>\n3025<\/td>\n838<\/td>\n5<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
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Different ammunition sizes for testing resistance ratings<\/figcaption><\/figure>\n

Bulletproof Glass Resistance Level Ratings<\/h2>\n

Many convenience stores, banks, and buildings with similar security needs opt for security levels 1-3. Purchasers must take weight and cost must come into consideration- especially for schools which are usually on a tight budget. The thicker the bullet resistant glass, the more costly it is to manufacture, transport and install. And like any glass, the framing that supports it plays a major roll as well- another expense. So this begs the question- at what point is bullet resistant glass \u201cthick enough\u201d? What becomes the balance of \u201csafe enough\u201d yet still cost effective? This has become the roadblock for legislation.<\/p>\n

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Bullet-resistant glass thwarts attempted robbery. Attribution: \u00a9 Raimond Spekking \/ CC BY-SA 4.0<\/a> (via Wikimedia Commons)<\/figcaption><\/figure>\n

Industry experts agree that more education is needed regarding the cost, integration and safety levels of bullet resistant glass so that the governments can choose the best path for protecting America\u2019s schoolchildren.<\/p>\n

Fore more glass-related information, check out our blog with topics ranging from auto glass<\/a> to home furniture glass, commercial glass, and everything in between.<\/p>\n","protected":false},"excerpt":{"rendered":"

There’s no such thing as bulletproof glass. This may come as a shock because of the portrayal that movies and pop culture make. We’ll break down the facts and talk about how testing plays a crucial role (and complicates) selecting the proper glass for different applications. Find out more here.<\/p>\n","protected":false},"author":5,"featured_media":2176,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"content-type":"","footnotes":""},"categories":[7,1352],"tags":[37],"_links":{"self":[{"href":"https:\/\/www.glass.com\/info\/wp-json\/wp\/v2\/posts\/2175"}],"collection":[{"href":"https:\/\/www.glass.com\/info\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.glass.com\/info\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.glass.com\/info\/wp-json\/wp\/v2\/users\/5"}],"replies":[{"embeddable":true,"href":"https:\/\/www.glass.com\/info\/wp-json\/wp\/v2\/comments?post=2175"}],"version-history":[{"count":0,"href":"https:\/\/www.glass.com\/info\/wp-json\/wp\/v2\/posts\/2175\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.glass.com\/info\/wp-json\/wp\/v2\/media\/2176"}],"wp:attachment":[{"href":"https:\/\/www.glass.com\/info\/wp-json\/wp\/v2\/media?parent=2175"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.glass.com\/info\/wp-json\/wp\/v2\/categories?post=2175"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.glass.com\/info\/wp-json\/wp\/v2\/tags?post=2175"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}