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NCJ Number
Law Enforcement Technology Volume: 20 Issue: 9 Dated: (September 1993) Pages: 38-41
M C Savine
Date Published
4 pages
This article reports on a study of the threats of roof- mounted police sirens to driver hearing and to audible radio communications and then offers recommendations.
In 1990, the author conducted noise-emission tests on police vehicles from seven police agencies in New York State. The tests were designed to determine whether or not the vehicle sirens were in compliance with the Federal noise-exposure regulations. A Metrosonics db 308 dosimeter, or sound measuring device with internal logic, was used to measure low, average, and maximum noise exposure levels at the driver's position. A total of 750 noise measurements were taken on 50 randomly selected vehicles. The study found that with the vehicle windows closed, sound pressure levels at the driver position did not exceed Federal safety regulations and thus did not pose a health concern; however, with the windows open, sound pressure levels above 115 decibels, which exceed Federal limits, were recorded in a small percentage of the vehicles. Even more disturbing, however, was the finding that even with the windows closed, the amplitudes of the roof-mounted sirens in 70 percent of the tests were so loud that it was difficult to hear tactical radio transmissions. The author recommends mounting sirens in vehicle grills, insulating the passenger compartment, using vibration isolation mounts, using noise- cancelling microphones, equipping vehicles with electric windows and functional air-conditioning units so car windows can remain closed, and documenting hearing exams for officers.