Audibility of warning signals while wearing level dependent ear-muffs

Status:

completed 04/2002

Aims:

Hearing protectors may decrease the audibility of acoustic warning signals. Therefore the use of hearing protectors was not permitted until 1996 in Germany while steering a vehicle in road traffic. But according to the European Directive (86/188/EEC) on the "protection of workers from risks related to exposure to noise at work" the employer has to offer suitable hearing protectors for working in noise zones. Noise zones are zones where the daily personal noise exposure of a worker exceeds 85 dB(A). Vehicles are generally not noise areas when operated correctly. In some vehicles, however, especially vehicles licensed as workmachines, the daily personal noise exposure sometimes exceeds 85 dB(A). The activities within this project were limited to the use of level dependent ear-muffs in noise areas in or at road vehicles where workers drive the road vehicle. It was to be determined, to what extent level dependent ear-muffs change the audibility of warning signals at noisy work places compared to conventional ear-muffs. The target given by the German minister for labour and social affairs and the German minister for transport was to select specific suitable hearing protectors.

Activities/Methods:

Suitable sounds at workplaces were grouped, which have been recorded on DAT-tapes. Relevant acoustic warning signals were selected. The audibility of warning signals during presentation of working sounds and while wearing level-dependent hearing protectors was compared to that obtained while wearing conventional (passive attenuating) ear-muffs by hearing checks in the laboratory.

Results:

Studies performed in the course of this project together with the results of two further studies by the German Federation of Institutions for Statutory Accident Insurance and Prevention (HVBG) were summarized as follows: The use of level-dependent ear muffs leads to an improvement in signal audibility under impulsive (e.g. punch presses) and low-frequency noise conditions. Signal audibility is not generally improved by such ear muffs, and often is even impaired. A poor transfer characteristic of the electroacoustic element of the ear muffs results in a reduction in signal audibility under continuous noise conditions. The results were employed during revision of the BG Rule concerning the use of hearing protectors (BGR 194, Carl Heymanns Verlag, Cologne, Germany).

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