From vandalism and natural disasters to terrorist attacks, one of the most vulnerable and potentially dangerous elements of a building is the glass in windows. One solid product that can help minimize damage and injuries is security window film—and such products are a natural in retrofit situations.
Existing glass in buildings was not designed to resist wind blown debris, earthquakes, gunfire, forced entry, explosions and terrorist attacks. Subject to such stresses, existing glass often breaks into lethal shards and falls or is hurled from the window frame, endangering building occupants and passers by. Broken glass also causes damage to the building that would not have occurred had the glass remained in its frame.
Security window film can improve the ability of existing glass to mitigate the impact of explosive force and wind blown debris. The primary function of security film is to hold glass intact in the event of it being broken. If a window with security window film breaks, the film holds the glass shards intact preventing them from becoming lethal flying or falling projectiles. In some cases, the glass may shatter but remain intact in its original frame.
The need to better protect glass in buildings has been sharpened after a series of natural disasters and international terrorist attacks during the late 1990s and culminating in the shock of September 11th. For example, according to the Downing Assessment, an unclassified report by the U.S. Secretary of Defense, broken glass in the terrorist bombing of Khobar Towers, a housing facility at the US Air Force base in Dhahran, Saudia Arabia, resulted in over 330 injuries and 19 fatalities. The report estimates 80-90 percent of those injuries were caused by broken glass.
Beyond rare terrorism incidents, most injuries from glass, says the Houston, Tex.-based V-Kool, Inc., a source from reflective and security applied films, center on people walking into or through a pane of glass. By the time an individual realizes that he has walked into the glass he has already broken the glass and does not have sufficient time to backtrack. As soon as the glass is broken, it falls and causes injuries to the knee and upper leg. Statistically, the next most likely area of injury is to the head, neck and shoulder. There are about 150,000 glass-related accidents in the U.S. annually.
No matter the cause of damage, there are products that can reduce the danger of injury and death from glass.
One option is laminated glass.
This is where there are two or more pieces of glass bonded by a polyvinyl butyral (PVB) plastic interlayer used in architectural glass products and in automotive and aircraft windshields. Many manufacturers including Guardian, Cardinal and Southwall Technologies make laminated glass.
Laminated glass can provide both insulation and solar reflectivity plus increased resistance to forced entry, wind blown debris, seismic and explosive force. Not all window frames can support the weight and thickness of laminated glass. With laminated glass, there is a trade off between energy and safety/security performance. Resistance to force also impedes the ability to break laminated glass for emergency entrance or egress though such concerns are not relevant in high rise applications.
Another option is security window film.
Security window film is comprised of either optically clear, tinted or reflective layers of polyester film (from 4-mil to 15-mil in thickness) that have an adhesive on one side so that it can be adhered to the interior surface of existing glass. Multiple layers of film can be laminated together, with commercially available overall thicknesses ranging from two to 15 mils. The material is packaged in rolls, with a maximum available width of 72 inches.
It is usually applied in the field with the glass and frame already in place. Occasionally film is applied on new glass before that glass has been installed. Typical film installations cover the visible portion of the interior surface of the glass all the way to the edge of the frame, but do not extend to the glass edge within the frame.
Film can be applied to both single pane and many types of insulating glass. Proper application of appropriate film to insulating glass does not impact integrity of insulating glass sealant or generate thermal stress to glass from uneven heat absorption. However, even proper film installation may invalidate glass and window manufacturer warranties. Security film with solar control and other energy saving capability greatly varies depending on the type of existing glass to which it is applied. Applied security window film is available with and without solar control capabilities.
When properly installed, this film forms an invisible protective coating over the glass. When the glass breaks, the film holds the glass shards intact, preventing them from becoming lethal flying or falling projectiles. In some cases, the glass may shatter but remain intact in its original frame.
Absorbs Shocks, Too
Because security window film has the ability to stretch without tearing, it can absorb a significant degree of the shock wave of an explosion. As this explosive force moves toward the glass and pushed it inward, the glass eventually cracks and breaks. However, the security film applied to the rear of this pane of glass continues to absorb the shock wave and stretches until it reaches the point that it can no longer bear the pressure, at which time it will burst.
In some cases, the shock wave, when great enough to break the glass, is not enough to shear the safety film. This results in the pane of glass being broken but held intact by the film. In these cases, not only are there no injuries, but there is no damage to the property inside the building. In other cases, the shock wave is sufficient to break the glass and shear the film. In many of these cases, the glass collapses in one pile attached to the security film with minimal damage and injuries. In multi-story buildings, security film may also prevent glass from falling out of its frames to the street below.
Both laminated glass, if properly installed in window frames capable of supporting its weight, and security window film, if properly installed in existing window frames, may mitigate the impact of explosions, forced entry, wind blown debris and seismic forces generated by earthquakes.
It is important to note that the ability of both laminated glass and security window film to mitigate the impact of explosions, wind, earthquakes and forced entry depends to a great extent on the relationship of the glass and film to the supporting window frames.
Window Frame Important
In the case of laminated glass, the window frame must support the weight of the glass in order for the total glass and window system to increase the ability to mitigate explosive and other forces. Just installing laminated glass in existing window frames may not prevent the glass from separating from the frames when force is experienced.
Similarly, the ability of security window film to empower existing glass and windows to mitigate explosive and other forces may increase if the film is not only applied to the glass, but attached to the frame as well. Many window film manufacturers, distributors and installers have developed retrofit film attachment mechanisms for securing the film to the window frame. Such mechanisms include securing bars, edge-to-edge dry lamination techniques and proprietary frames and sealants.
One final film twist: V-Kool markets a spectrally selective security film that also blocks heat while transmitting normal levels of light.
Beyond helping to minimize glass break damage, this approach saves energy dollars by minimizing overheating while insulating against heat loss.
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