![]() Because of its expense, this procedure is generally limited to new construction and major renovations. To achieve higher levels of protection, the window glass must be replaced and the window frame should be reinforced. For deployed locations, removing the windows and covering them with plywood minimizes the danger. ![]() The retrofit techniques are generally thought of as providing a lower level of protection than the glazing replacement techniques. The designs for this and other types of retrofit devices are complicated and require specialized engineering-analysis tools. Another retrofit technique is to use fragment-retention film with a metal bar placed across the window. The curtains are generally used with fragment-retention film. The curtain or drape catches the glass fragments. Another retrofit approach is to install a blast curtain or a heavy drape behind the window. The glass fragments stick to the film, and the film either stays in the window frame or falls into the room in one or more large, relatively nonhazardous pieces instead of many small, lethal pieces. The film does not strengthen the glass but when the glass breaks, it keeps the fragments from spreading throughout the room. The film is a plastic (polyester) sheet that adheres to the window glass with a special adhesive. One of the most common means of decreasing the hazards from broken glass is to install fragment-retention film on the glass. There are two basic approaches to mitigating the effects of bomb blasts on glassretrofitting the windows with film or curtains and using blast-resistant glazing. Historically, glass fragments have caused about 85 percent of injuries and deaths in bomb blasts. Figure 3-4 shows common perimeter barriers for stationary or moving vehicle bombs. Spaces between barriers should be no greater than 4 feet. The cables in the reinforced fence also have to be anchored into the ground or partially buried. When barriers such as the Jersey barriers and planters are used to stop moving vehicles, they must be anchored into the ground to be effective. Barriers capable of stopping moving vehicles include chain-link fences reinforced with cable, reinforced concrete "Jersey barriers", pipe bollards, plantersditches, and berms. Aggressors driving through such barriers are likely to be noticed. Common applications include chain-link fences, hedges made of low bushes, and high (over 8 inches) curbs. Anything that presents a fixed obstacle will work for the stationary vehicle bomb. Perimeter barriers are fixed barriers placed around the entire perimeter of a standoff zone. Barriers for the moving vehicle bomb need to stop the vehicle's motion they must be much more substantial. Crashing through a barrier would be noticeable. The assumption is that the aggressor's goal in the stationary vehicle bomb is to park the vehicle and sneak away without being noticed. The goal for that barrier is to make anybody driving through the barrier noticeable. The barrier used for a stationary vehicle bomb does not have to stop a vehicle's motion. The type of barrier used for a moving vehicle bomb differs from the barrier used for a stationary vehicle bomb. Two types of vehicle barriers are used for vehicle bombsperimeter and active barriers. The nonexclusive standoff zone provides the advantages of allowing better use of the parking areas and limiting the number of vehicles that need to be searched at the outer perimeter.ģ-10. ![]() Figure 3-3 shows a nonexclusive standoff zone. Trucks cannot enter the outer perimeter, since it is established based on what they can carry. With these two perimeters, cars can enter the outer perimeter without being searched but they cannot enter the inner perimeter. The outer perimeter is set at a distance associated with the weight that can be placed in trucks (refer to TM 5-853-1). The inner perimeter is set at a distance corresponding to the weight of explosives that can be concealed in cars. Therefore, a nonexclusive standoff zone includes inner and outer perimeters. A nonexclusive standoff zone takes advantage of aggressors being able to conceal a smaller quantity of explosives in a car than they can in a truck. A nonexclusive standoff zone is established in a location having a mixture of cars and trucks (with relatively few trucks). ![]()
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