Industrial impulse noise, crest factor and the effect of earmuffs.

Abstract

Noise measurements were taken inside and outside earmuffs worn by 238 workers at 21 industrial plants in order to evaluate exposure to noise and to measure the attenuation by earmuffs used at workplaces. The means of the equivalent noise levels were 93 dB outside the earmuffs and 76 dB inside them. The mean earmuff attenuation was 17 dB. The standard deviations of each of these three values was 6 dB. Thus 90% of the employees wearing earmuffs experienced equivalent noise levels of lower than 85 dB(A) inside the earmuffs. In addition to equivalent noise level, the impulsiveness of the noise was determined based on the cumulative distribution of the crest factor of the signal. The impulse percentage F15 denotes the percentage of the total measurement time when the peak level exceeds the rms level by at least 15 dB. The mean impulse percentage F15 was 1.6% outside earmuffs and 0.8% inside earmuffs. The results showed that earmuffs also attenuated the impulsiveness of noise. The shipyard noise had the highest impulse percentage; the noise in printing plants and papermills had the lowest impulse percentage.