Volume 35, Number 12, December 2000
Be-Bes and Bazookas
Which security glass is the right security glass?
by Dez Farnady
The proper selection or specification of security glass requires a lot more than the usual request to "just get me a price on some bullet-proof glass." When I get a request like that my first question usually is: "Do you want to stop a be-be or a bazooka?" A non-specific request creates the possible liability that may come with the selection of the wrong glass. It is not enough to stop the be-be when bazookas are being shot your way. The required security level must be determined and the need clearly identified so the proper product can be provided.
Security glazing has become a very complex and sophisticated business with a great variety of requirements and an endless number of options.
Security takes many forms. You can be secure from an undesired audience with multi-layered laminates that reduce sound transmission. Polyvinyl interlayers can provide protection from storm damage caused by flying debris. Forced entry-resistant products use thicker vinyl interlayers to provide the marketplace with increased security and multi-layered laminates, in various forms, can provide bullet-resistant glazing.
We can reduce weight while still stopping a bullet with multi-layered polycarbonate and acrylic sandwiches. We can slow down the spread of fire with some high-end, specialty multi-layered products that literally burn away layer by layer. Glass-clad polycarbonates can provide protection for institutional applications where attack-resistant glass products need to meet a wide range of very special requirements.
Forced entry-resistant and bullet-resistant glazing products are rated by levels and are tested for specific performance criteria. Burglar-resistant products from multiple-impact to high-energy impact are tested with various implements like sledgehammers and propane torches. Bullet ratings start at level one for medium-powered handguns and go to level eight for rifles with a muzzle velocity of 2,750 fps. Storm window testing for windborne debris includes tests for flying two- by- fours and possibly even for Dorothy's house hurtling through space all the way from Kansas.
However, it's not all wonderful technical advances. There are some down sides to each product. Too many layers of glass and vinyl create optical distortions and become very heavy. Even at the minimum bullet-rated thickness of 13/16-inch the glass will weigh nearly 12-pounds per square-foot. The multi-layered, acrylic-polycarbonate combinations are light in weight but only have the limited surface durability of standard mar-resistant polycarbonates. All of these products come with some size limitations and create problems when you try to glaze these extra thick materials in standard glazing pockets. Generally that is not a good idea because these products usually require tested and rated frames that also add to the cost. All of these products have difficult jobs to do so they usually come at a very high price.
There is no one type of "bullet-proof" glass, just as there is no one type of bullet. The glass industry has developed security glazing product lines that enable you to fill a multitude of needs if you can only define the requirements. These products do not belong in the routine of everyday business. They are highly specialized to satisfy very specific needs.
Institutional requirements are usually well researched and are generally clearly specified at design time. It is at replacement time that I get the call to provide some of "that prison glass." The same thing happens when a developer wants an upgrade, or a remodeler wants to lease to a jewelry store, or a service station wants to change the cashier's window and asks for "bullet-proof" glass.
I would be paranoid to think that the violence of the 21st century is motivating the development of security products. I choose to believe that we are using security glass products because we can. We can open up both exterior and interior spaces with glass products without compromising security.n