Aim: For the workplace conditions leading to
occupational hearing impairment, publications
– for example the German occupational
disease bulletin BK-2301 (BMGS 2008) – specify
the required exposure duration at a daily
noise exposure level of 90 dB(A) or 85 dB(A)
only imprecisely as “long-term” or “for some
years”. For the purposes of occupational medical
care, such information is not adequate for
the prediction of noise-induced aggravation
of already existing hearing loss. Therefore,
occupational medical care and assessment
of work-related criteria within the scope of
the appraisal require an Effective Noise Dose
to express the life-time occupational noise
dose determined on an acknowledged scientific
basis from the data for existing exposure
periods or expected future periods. Then this
noise dose would only have to be compared
with a threshold value.
Methods: Noise-induced equivalent hearing
threshold shift curves are calculated on the basis
of ISO 1999:1990. An Effective Noise Dose
is developed to express the occupational
noise dose in a form which allows the noise
exposures during all periods to be taken into
account hearing threshold shift equivalently.
Results: It is demonstrated that the equivalent
hearing threshold shift curves are independent
of sex, age and of fractile for the
fractiles Q < 0.50. The Effective Noise Dose is
calculated using the given mathematical formulae
and algorithms.
Conclusions: For occupational medical care
purposes the noise-induced equivalent hearing
threshold shift curves can be consulted to
assess the risks of future exposure – for example
in regard to additional measures within
further employment in a noisy environment of
persons suffering from hearing deterioration.
Based on the procedure presented here,
adapted from ISO 1999, an Effective Noise
Dose is deduced for an individual of that half
of the population which is most sensitive to
hearing loss or hearing impairment; this Effective
Noise Dose is valid for the working life
exposure of that individual.
