A study conducted in 1979 found that most of the 150 Virginia bank customers surveyed did not mind the presence of protective barriers. In addition, bank tellers who worked behind the barriers felt safer with the barriers. The survey found that banks protected by bullet-resistant barriers figure in less than 3 percent of all bank robberies in the United States and that barriers are more cost-effective than armed guards. These and other statistics indicate the utility of these barriers. Companies planning installation of barriers should consult security managers in the area to determine the level of threat and what weapons barriers need to resist. The security manager should approach manufacturers of bullet-resistant barriers and gather information about their products. Features to be evaluated include ballistic resistance (weight and velocity of bullet and number of impacts) and resistance to temperature change. Companies should also check into the product's performance in these areas: spalling, (disintegration or fragmentation on the side opposite the impact of the bullet) maintenance, light transmission, weight, cost, frequency of replacement, ease of installation, resistance to fire, ventilation, acoustics, and lighting requirements. Security managers should ask for test results of the materials being considered. Available testing standards include those prepared by the Law Enforcement Standards Laboratory of the National Bureau of Standards and the British Standards prepared by the British Standards Institution.