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A View to Security and Safety Laminates Stall Forced Entries and Contain Shards
November, 2007
By Ron Phelphs and Bob Alsip
Glass is the weakest link in building safety and security. Unprotected windows offer little or no resistance to forced entry or an explosion.
Standard annealed glass is used for most windows commercially and residentially for single pane, double pane and triple pane windows, with or without Low E or reflective coatings. It tends to break easily upon impact, produces large sharp shards and offers very little resistance for security applications.
Tempered glass is typically used for entrance glazing, sloped and horizontal glazing and any glass installed in close proximity to the floor. Tempered glass is more difficult to break, but breaks violently into many small pieces as a result of blunt force impacts. It can also break spontaneously due to sulphide inclusions created during the manufacturing process.
Laminated glass typically consists of an inner layer of plastic (i.e. PVB) sandwiched between two separate pieces of annealed glass, and tends to remain intact due to the inner layer material. In security applications, a nominal inner layer thickness of .060 (60 mil) or thicker is generally used.
Wired glass typically consists of a thin wire mesh embedded into annealed glass. Contrary to what many property managers may believe, wired glass does not address either safety or security concerns. Its purpose is to meet fire code regulations. It offers very little resistance to breakage or penetration and produces sharp shards when broken.
Most security systems focus on monitoring rather than truly 'hardening' the building perimeter. Typical security detection systems indicate when an intrusion has taken place, so glass-break detectors may not offer any additional advance warning over motion sensors if the glass is penetrated quickly.
World events have created additional safety concerns. Blast consultants note that the primary threat to building occupants and passersby is flying glass shards in the event of an explosion.
TEAR RESISTANCE
Security laminate can slow down the forced entry process. For annealed or laminated glass applications, tear resistance is particularly important because it makes it more difficult to create an opening large enough to climb through. Optimum tear resistance is achieved using thinner and more flexible micro-layered laminate technology. A 39 micro-layer 6 mil laminate has five times the tear resistance of a basic polyester laminate of similar thickness.
For glass doors and sidelights and especially with tempered glass applications, break- strength is the most important attribute. Thicker films tend to have higher break-strength, which is particularly important in making it difficult to gain access to the door locks.
Additionally, tempered glass must be bonded to the frame. Otherwise, it will simply break away along the frame when broken, opening easy access to the property.
Security laminates combined with glass-break detectors create a dynamic combination of detection and deterrence since the intruder can be detected while still being restricted to the outside of the building. Solutions are typically categorized as to the level of protection they provide as per the generally accepted Loss Control Standards of the insurance industry.
The proven effectiveness of security laminates has been further validated by the fact that they are included in training sessions on crime prevention through environmental design (CPTED) provided to OPP officers and other policing agencies.
The most important attributes of laminates for blast mitigation are tear resistance and flexibility. When a blast occurs, glass shards may penetrate the laminate and its ability to resist tearing dictates how effectively it will protect occupants from flying glass.
Micro-layer laminates are ideally suited for this application since they are able to expand to absorb the blast and also offer the highest tear resistance to maintain the glass integrity. Basic polyester film (7, 8 or 9 mil) laminates simply cannot provide the same level of elasticity and, therefore, tend to offer less life safety protection.
How the laminate is bonded to the frame is the other critical component. When installations do not use a bonding system, such as an architectural adhesive designed for blast mitigation, there is increased risk of the entire pane becoming detached from the frame and entering the building.
It must be noted that security laminate installed on standard commercial insulated or double pane windows does not provide an adequate safeguard against bullet penetration from commonly used firearms.
Ron Phelphs and Bob Alsip are with the Convenience Group, a certified dealer of security and safety laminates for windows. For more information, see the web site at www.windowfilm.ca.
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