BY RONALD E. SHAW AND JAMES ONDER, Ph.D.
Emergency responders have seen many innovations in the automobile industry within the past decade, such as supplemental restraint devices, automatic rollover protection, new construction methods, and lighter and stronger construction materials. A recent innovation is enhanced protective window glazing, or EPG. It is a resistive glazing that provides added protection during a crash and from illegal entry and could represent an additional challenge at vehicle extrications.
 Photo courtesy of authors. |
A key component of EPG is a plastic interlayer or film composite made of a substance called polyvinyl butyl (PVB). The product will resist penetration from direct blows with a hammer; it is being promoted as an antitheft deterrent. The EPG will be used on glass in side and rear automobile windows and can be clear or tinted. A visible border hides the underlying bonding agent.
For decades, tempered glazing has been commonly found on most vehicles on the road today. Tempered glass is heated to a high temperature and quenched very quickly with high velocity air. Quenching cools the glass surface faster than the core, causing the outer surface to be in compression and the inner core to be in tension. When the outer surface is struck, the frozen-in stresses are released, causing the glass to shatter uniformly into hundreds of pellets. The shattering of the tempered glass into small pellets during a crash prevents vehicle occupants from receiving an injury commonly referred to as a “glass necklace.” This type of injury was common when a vehicle window was constructed of plate glass in the earlier days of the automobile evolution. Plate glass may still be found on some heavy trucks and buses on the road today. Laminated and tempered safety glass has helped eliminate this type of injury.
During the victim access phase of vehicle extrication, rescue personnel using common hand tools can easily break tempered safety glass. But tempered safety glass offers the occupant little protection from vandals, thieves, and carjackers. EPG offers a degree of increased protection to the occupant during a crash and from would-be carjackers or vandals. EPG has characteristics similar to laminated windshield glazing and should not present additional concerns to the emergency responder.
Responders can remove EPG with the same techniques and tools used for laminated windshield glazing. EPG also gives the responder the option to leave the glazing in place, reducing the chance of injury from broken glass fragments and decreasing the overall extrication time.
EPG is now available as standard equipment on the Mercedes Benz S-Class and Audi A8 and as an option on the Audi A6 and Volvo S80, S70, and S60 models. In Mexico it has been offered in the Daimler Chrysler Cirrus and Stratus. EPG has also been available in Europe for Audi and Peugeot vehicles. The Enhanced Protective Glass Automotive Association (EPGAA) expects U.S. manufacturers to use the glazing material within the next two to four years.
TESTING EPG
Extrication.Com, an on-line resource for vehicle extrication specialists, contacted the EPGAA requesting that independent extrication specialists be allowed to perform tests on this new glazing material. The testing would allow the specialists to share their findings with responders prior to EPG’s introduction on the street. The EPGAA agreed that it was vital that responders know how to cope with EPG before it was introduced on the American automotive market.
Fire service instructors with expertise in vehicle extrication conducted the testing. Test members received an overview of EPG, including the properties that make it resistant to vandals and intruders (carjackers). The test team then determined its own testing procedure and the equipment to be used. The bench testing of the glazing took place inside a machine shop where a specially designed test stand was bolted to a cement floor. Eighteen replaceable windows specifically designed for three test doors were acquired from a local salvage yard. As the individual tests were completed, the doorframe was removed and the tested glazing replaced for the upcoming tests. Each test was documented on film and in photos.
Team members started with common hand tools currently used for removing tempered glass, such as the spring-loaded center punch and other striking tools. They progressed to common forcible entry tools and more specialized glass removal tools. The striking tools produced small, localized spider patterns with elongated cracks, as they would on windshield laminate. The test team found that any tool currently used for laminated windshield glazing will effectively cut EPG and that no specialized tool would be required. However, to the uninformed responder with a spring-loaded center punch in hand, gaining access could be challenging.
For an experienced test person using specific tools, glass removal seemed effortless. With a partially open window, one test member, armed only with gloved hands, used brute force to effortlessly snap the glazing. The tests revealed that there was little, if any, difference between the properties of laminated windshield glass and those of EPG.
TOOL TESTING RESULTS
Tools were rated on the following criteria: cutting performance, price, ease of operation, specialty tool designed for multiple uses, mobility, and need for an external component such as a power source.
The Glasmaster hand window saw by Wehr Engineering was a popular choice because of its low cost and ability to remove all types of glass, not just laminated glass. Within a few tries, even the most inexperienced user could master the fast cutting tool. The cordless Sawzall (18v) by Milwaukee Electric Tool Company could cut almost as fast as the other tools, and many departments may already own a cordless/corded reciprocating saw. The best choice of blades for laminated glazing was the Milwaukee Ax wood demolition blade with 5
Other tools performed poorly for this application. The spring-loaded center punch commonly used to clear tempered safety glass was of no value in removing EPG. The center punch caused only a spider pattern and pierced the laminate. While the halligan can be used to make a purchase point for tools such as the sawzall, alone it performed poorly. After repeated blows, the common hand maul eventually smashed through the glazing or caused the EPG to fold or buckle in. A small hatchet cut the EPG, but the tool took longer and is more hazardous to use during extrication than other cutting tools. Handheld striking tools that concentrate a tip force from a blow to shatter tempered safety glass proved to be of little value as well. However, some multifunctional handheld striking tools may be of some value as pry tools to separate and lift sections of glazing after saw cuts are made. The circular saw cut the material cleanly and quickly but produced an unacceptable level of dust and directed fragments at the operator. Rotary-type cutting tools can cut EPG but at a rate undesirable for rescue work. It has been reported that rotary bit tools work well for removing polycarbonate automobile glazing. For this reason one tool that cut polycarbonate efficiently was also used to test its EPG-cutting capabilities. Having a universal cutting tool was the goal of the test team.
BENEFITS OF EPG
It should be apparent to a responder confronted with EPG that it is not tempered safety glass; it will not shatter when hit with a striking tool or a spring-loaded center punch. EPG may be identified by the EPGAA label. Any tool currently used for cutting laminated windshield glass can be used to cut EPG, including the flathead ax. If possible, leave the glazing in place or roll down the window inside the frame as required.
EPG will not shatter into small pellets, so there will be less concern for flying fragments than with tempered safety glass. However, when removing any glazing, wear proper personal protective equipment, including eyewear and a dust mask. Shield victims with a protective covering. With overturned vehicles, it may be beneficial to leave EPG intact and in place; this can reduce the total extrication time by allowing responders to move on to the next task. Responders must decide whether to cut or remove the EPG.
Currently, almost all U.S. and foreign vehicles come equipped with the standard tempered safety glass. During a rollover, unrestrained occupants can be ejected as the tempered glass shatters. The glass pellets and fragmentation from tempered glass can cause soft tissue injuries to the body and eyes, unlike EPG. It is clear that EPG will reduce the risk of soft tissue injury. Also, EPG has the benefit of increased structural strength and may help prevent the occupants from being ejected during a rollover. Vandals, thieves, and carjackers may also be deterred or at least slowed down in their efforts. Windows designed with EPG reduce the outside noise by as much as three to four decibels. Also, EPG
OTHER NEW GLAZING MATERIALS
EPG is now in competition with polycarbonate glazing for passenger vehicles. However, at the present time polycarbonate glazing cannot be used in movable windows. There are two inherent problems with polycarbonate. Although polycarbonate is extremely strong, it scratches easily. Scratching is an undesirable trait in glazing used for movable windows. Also, because of polycarbonate’s ability to flex, the glazing may flutter if the window is left partially open while traveling at highway speeds. To avoid flexing, the manufacturer could thicken the edge by blowing a gas bead into the leading edge of the glazing. However, this is not desirable, since the industry is already tooled for the current thickness. Increasing the thickness would now cause the industry to retool for the polycarbonate. This could be disastrous if the industry decided to stop production and revert to glass. At the same thickness, polycarbonate is much stronger than glass and has not broken during crash tests. It keeps the occupants inside the vehicle with no soft tissue cuts from the glazing, which may occur with glass windows.
BMW has used a resistive glazing with seven layers of laminated material, which contains a polycarbonate interlayer. This product is even more resistive to vandals than the featured glazing, but the same tools currently used for cutting EPG and laminated windshield glass may be used.
The presence of EPG may actually decrease the time required to perform vehicle extrication. When responders are properly trained in its removal, EPG will prove to be no more restrictive than ordinary windshield material. The EPGAA will soon release an EPG training program for first responders. For more information, visit the EPG Web site at http://www.epg.com.
RONALD E. SHAW is a lieutenant in the Plymouth (MA) Fire Department and a fire service instructor. He is the founder of Extrication.Com, an on-line resource for vehicle extrication specialists.
JAMES ONDER, Ph.D., is a vehicle safety specialist and communications instructor in Washington, D.C. He is also an instructor with Extrication.Com.
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