Security Glazing for Exhibit

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The transparent glazing material chosen for an exhibit case can provide display objects a high level of protection against theft and vandalism

What is security glazing?

Security glazing includes a large group of laminated glass and plastic products that combine the advantage of both materials. Security glazing also referred to as security glass can be used in cases:

• to protect against attack from forced entry, bullets and bombs;
• to increase case stability in areas prone to natural disasters, such as earthquakes and hurricanes;

There are a number of important points to understand when using security glass as opposed to other glazing materials.

• The static load strength of laminated glass is no stronger than monolithic glass.
• Security glazing is designed to stay in the frame when broken.
• Multiple layers of differing materials can affect the transparency of security glazing; to increase the transparency, request water white glass such as Starefire and AGF.
• Using security glazing may add significant cost to a project.
• These materials usually need to be special ordered; factor extra time into the production phase.

There are two main types of security glazing: (1) laminated glass of two or more glass sheets with interlayers of polyvinyl butyral (PVB), and (2) glass combined with polycarbonate which can be manufactured as a glass-clad system or an air-gap system.

1. Laminated glass: The thickness of the PVB layers usually ranges from 0.030" to 0.120". Extensive testing by the manufacturers indicate that PVB does not yellow over time. Inhibitors in some PVB absorb 99.9% of UV radiation up to 350 nm. While an extremely stable product, prolonged exposure to water, water vapor, solvents, or solvent vapors can cause delamination. Some manufacturers have begun to produce lighter weight laminated polycarbonate systems and suggest that they are comparable to laminated glass.
2. Glass/Polycarbonate: These products offer good protection against forced attacks, especially in situations where a prolonged attack on an unmonitored exhibit case is possible. A major disadvantage of polycarbonate is its tendency to yellow; most manufacturers only guarantee the material for 5 years. These units are manufactured as a glass-clad or air-space system.

• Glass clad: Glass is interlaid with sheets of polycarbonate adhered to the glass with urethanes. The tendency to delaminate because of different expansion and contraction properties has been improved in recent years.
• Air space: An air space between the two materials is maintained by a spacer. Leaks along the spacer can cause a problem as secondary reflections. Because the plies are not laminated together, it is better to request a coated polycarbonate sheet.

How do I choose a security glazing?

Before choosing a security glazing, the exhibit design team must determine the level of danger to the collection. Factors to consider are the amount of time and tools an assailant may have to attempt forced entry, what type of ballistic attack is likely, and the probability of a bomb threat. Consult a security consultant or major glass company.

Basic points to consider are:

• When evaluating product information, it is important to find out which testing method was used to assess the glazing; different tests have different requirements.
• Generally, high security systems are thicker. Also, as the panel size increases the glazing must become thicker to resist entry. Thicker PVB interlayers provide more resistance against forced entry than thinner interlayers. Polycarbonate layers offer greater resistance to forced entry than PVB.
• Several plies of thinner glass offer more protection against forced entry and ballistic attack than fewer plies of thicker glass.

A comparison of security glazing products is given below. It assumes the total thickness for the material is always the same.
When using a single, monolithic glass panel, annealed glass has the weakest static load strength; heat strengthened is considered twice as strong; and fully tempered is considered the strongest.

In terms of protection against ballistic attack, annealed glass is preferable as the first bullet that passes through will simply create a small hole and the rest of the glass will break into large sheets which hold together rather well. Tempered glass, when hit with a bullet, will break into many small pieces that fly out the back of the window. Tempered glass, however, does provide the most protection against bombs. In terms of forced entry there is little difference between the glass types as it is primarily the plastic which is providing the protection.

Comparison of Systems

COST (greatest to least expense)	FORCED ENTRY (greatest to least attack resistance)	BALLISTICS (least to greatest attack resistance)	BOMB RESISTANCE (greatest to least resistance)
Polycarbonate Monolithic acrylic Glass/polycarbonate - air gap and desiccant - glass clad - air gap Glass laminate (PVB) Monolithic glass	Polycarbonate Glass/polycarbonate (all systems are equal) Acrylic/glass laminate Monolithic glass	Glass/polycarbonate (all systems are equal) Glass laminate (PVB) Acrylic/polycarbonate Monolithic glass	Polycarbonate Laminated Glass Monolithic Glass Glass/Polycarbonate (all systems are equal)

Note on insulated glass

None of the systems listed above increase the insulating value of glass. Insulated glass incorporates an aluminum spacer filled with a desiccant, air tight adhesives, and purging the space first before sealing. One company (Viricon) produces an air-gap security system following insulated glass specifications; this increases the cost.
Most often, an air space is introduced to affect the R value (the overall resistance to heat transfer through a material). As an example: 1/4" glass has an R value of 1.01; the R value of a 1/2" glass is 1.03. In contrast, two 1/8" pieces of glass separated by 1/4" of air increases the R value to 1.6. The added air space makes the system thicker.

Are there special framing requirements for security glazing?

Security glass itself is often stronger than a conventional window frame and mounting hardware. A strong frame is required to withstand the shock that is first absorbed by the laminate and then transferred to the frame. Heavy-gauge aluminum is adequate for most situations; an exception is the potential of a bomb blast directly next to the case.

How are security glazing products tested to determine their security benefit?

There are standardized test procedures that rate a glazing's resistance to ballistic and forced entry attack.

• UL 972 Underwriter's Laboratories subject samples to a number of vertical impacts from a
• 5 lb. steel ball at various temperatures (ballistic).
• Department of State (National Institute of Justice) ASTM F1233-89 test sample for resis- tance to forced entry using a large range of typical forced-entry implements ranging from
• a sledge hammer to ripping bar to methylene chloride.
• WFML test elevates resistance to weapons that prisoners are likely to have and therefore does not take into account weapons which may be available to assailants outside of a prison. Results from this test are not completely useful for museums.

Unfortunately, different manufacturers use different tests. For instance, a material fails the National Institute of Justice requirements if there is any spall at all while the material will pass the UL 972 test as long as a projectile does not penetrate the laminate and large fragments of glass are not forcibly thrown from the rear a distance greater then 18".

Products, Manufacturers, and Suppliers

1. Laminated Glass Panels

• Monsanto
• Du Pont
• Viracon, Inc.
• Northwest Industries Guardian

2. Polycarbonate Panels

• General Electric
• Viracon, Inc.
• Laminated Glass Corp.
• Northwest Industries Guardian