Progressive noise induced hearing loss caused by hearing AIDS, a dilemma for the worker and the expert alike

Abstract

Investigating cases of noise induced hearing loss the expert is often confronted with the situation that the hearing loss is progressive although the noise exposure has been reduced to almost non-damaging levels. Other causes such as age, hereditary deafness, head injuries, blasts, internal diseases can be excluded. Hearing aids as sources of damaging noise? By consulting the protocol of the hearing-aid acoustician and by own examinations the expert should obtain the following data: loudness level that yields best discrimination score of speech; level of discomfort for tones and speech, discrimination score that is achieved under free field condition with a speech level of 65 dB, using the hearing aids. Furthermore he should explore the circumstances under which the hearing aids are used: how many hours per day, at what occasions etc.? It is likely that in using the hearing aids they are adjusted to emit an intensity level identical to the one yielding the optimal discrimination score. If this e. g. is 100 dB and the hearing aids are used for 2 hours per day this would be equivalent to an exposure to industrial noise of 94 dB (A) for 8 hours daily without ear protection. Among all individuals working under industrial noise exposure today only about 1 - 2 % having unusually vulnerable inner ears will suffer a noise induced hearing loss. On the other hand workers in industrial noise are accustomed to loud noise levels, usually have a raised threshold of discomfort and therefore are likely to adjust their hearing aids to such high intensities. The expert will have to decide whether in an individual case the industrial noise exposure or the use of the hearing aids is the dominant risk for further damage. The consequences in respect to the regulations of the workers' health insurance are discussed.