Author(s)Riach, Douglas A.
Noise and hearing.
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AbstractThe purpose of this thesis was to critically investigate the noise produced by the sirens fitted to South Australian Police general patrol vehicles and calculate if this noise was of an intensity to cause noise induced hearing loss. Previous studies in Western Australia and in South Australia examined noise emissions from emergency vehicle sirens for the purpose of selecting the most suitable siren for emergency vehicles, this being the siren emitting the greatest intensity of sound. This study has researched emergency vehicle sirens from the perspective of employee exposure to siren noise. Noise levels were recorded from inside the police vehicles using a hand held digital sound level meter while the vehicle was driven under driving conditions of stationary, 60 km/h, 80 km/h and 100 km/h. Noise level readings were taken with the front windows closed and open . South Australian police sirens have three distinct settings with differing noise outputs. The change in vehicle speed was found to affect the noise intensity within the vehicle for all 3 siren types. The peak noise level recorded was with the windows open and the vehicle travelling at 100 km/h ( 95, 94 and 97 dB(A) for the three sirens respectively). Closing of the front windows when stationary and when driving at was found to reduce the noise intensity within the vehicle. The greatest reduction from closing the windows was recorded at 100 km/h. This reduction was 11, 9 and 7 dB(A) respectively for the three siren types. Siren type one was the siren normally used by the South Australian police, consequently the majority of exposure by South Australian police employees is to siren type one. These sirens produced a peak internal vehicle noise Intensity of 95 dB(A) at 100 km/h with the windows open and 84 dB(A) at 100 Km/h with the windows closed . The reading of 95 dB(A) is greater that the 90 dB(A) eight hour continuous exposure limit set by the South Australian Occupational Health Safety and Welfare Act of 1986. The maximum exposure time for unprotected ears using the 90 dB(A) eight hour equivalent continuous A weighted sound pressure level (Laeq,8h) would be 2 hours and 30 minutes (150 minutes) . The assumption of this study was that noise intensity levels in excess of 90 dB(A) Laeq,8h will cause noise induced hearing loss. Therefore the noise intensity recorded from the vehicle siren tests at 100 km/h with the windows open have the potential to cause hearing loss if the duration exceeds 150 minutes. The review of existing records of vehicle pursuits showed that between January 1 1998 and December 31 2001, there were three instances where the exposure to siren noise exceeded the 150 minute exposure period. This study found the closing of the windows to reduce the noise intensity at all speeds and all sirens types to below the 90 dB(A) Laeq,8h. It is therefore recommended that all police vehicles whilst using the sirens close all windows to reduce the noise intensity within the vehicle.