Risk of hearing loss caused by impulse noise

Status:

completed 08/1988

Aims:

The method employed until 1989 in accordance with the German accident prevention regulation (UVV) "Noise" to assess impulse noise at the workplace implied an impulse coefficient with respect to the equivalent permanent sound level. In the revised UVV "Noise" as of 1st January 1990, which was intended to transpose the European Directive 86/188/EEC on noise protection at the workplace into German law, this coefficient is missing. Since, as a result, the assessment levels of workplaces with exposure to impulse noise are reduced by about 3 to 10 dB(A), the problem is to know whether the latest findings on the effects of impulse noise justify the abandonment of the impulse coefficient, and which measure is best suited to describe the risk of hearing loss related to impulse noise exposure.

Activities/Methods:

Once the most important studies on temporary threshold shift (TTS) and the results obtained from animal tests had been viewed, the activities focussed on retrospective studies into permanent threshold shift (PTS). In addition, a new PTS-study was conducted by the BIA which included four building professions: masons, concrete workers, carpenters and pipe fitters. On the basis of the hearing loss model described in ISO 1999 "Acoustics; determination of occupational noise exposure and estimation of noise-induced hearing impairment", the hearing impairment data available for these persons were used to calculate the corresponding sound levels. The thus obtained impairment-equivalent level L* was then compared to the actually measured energy-equivalent sound levels.

Results:

In the majority of studies, the equivalent permanent noise level without additional impulse coefficient turned out to be a useful measure for the assessment of impulse noise, too. Only a few studies speak of small coefficients of not more than 5 dB(A). BIA's own study in the building sector showed that the use of an impulse coefficient leads to an enormous overestimation of the hearing impairment risk compared to a level-equivalent permanent noise exposure. Against the background of these findings, the modified measuring method in the revised UVV "Noise" - based on the equivalent permanent noise level - appears justified. To protect the hearing against extremely high, hazardous impulse noise, it is nevertherless necessary to take also account of the simultaneously introduced limit value for peak sound pressure levels which was fixed at 140 dB.

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