Effectiveness of hearing protection devices in the hazard reduction of noise from used tractors

摘要

Old and worn agricultural tractors show typically high noise levels, due to the natural deterioration of the engine, the gearbox and other components of the machine (tyres, exhaust). Despite the limit of technical obsolescence of tractors being commonly fixed at 0 yr, a large number of older machines are still in use in Italy. The noise produced by 60 used old tractors, working in farms located in Northern Italy, was recorded with the aim of ascertaining to what extent the use of the hearing protection devices (HPD) could significantly reduce the noise perceived by the driver. The performance, in terms of noise reduction rating and single number rating of 40 earmuffs, 54 earplugs and 27 ear canal caps was examined. For every tractor, the use of all 121 HPDs was simulated, to determine both the best and the worst conditions. Considering the Occupational Safety Health Administration and National Institute for Occupational Safety and Health recommendations for decreasing the laboratory noise reduction ratings (to take into account the “real-world" attenuation), it can be concluded that, on average, 10 dB(A) of attenuation can be achieved. As the average noise level found at the tractor driver's ear was about 87-88 dB(A), with a maximum of 101 dB(A), this means that using the HPDs the noise could be reduced to 77-78 dB(A), up to 90-91 dB(A). This may be considered a fairly good result, but it should be recognized that the effectiveness of HPDs may vary widely from worker to worker, depending on correct wearing and wearing time.