Hearing impairment calculator

Screenshot of the Software

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Screenshot of the Software
Source: IFA

ISO 1999 provides an algebraic model for estimating the hearing impairment of populations due to threshold shift associated with age or in addition due to noise exposure of that populations when uniformly exposed.

For the calculation the following input is used:

  1. the A-weighted noise exposure level
  2. the exposure time in years
  3. the age in years and
  4. the sex.

The estimations of the model are limited to populations without any hearing impairment due to non-job related exposure.

The calculation results in hearing threshold shifts for frequencies 0.5; 1; 2; 3; 4; 6 kHz and for fractiles 0.05 to 0.95. The fractile 0.05 means for example, that 5% of the noise exposed individuals are expected to show a hearing threshold shift, which is equal to or larger than the value read off at the y-axis of the diagram at 0.05 fractile.

The PTS (permanent threshold shift) is composed of two parts:

  1. one part associated with age (that part complies exactly with curve "75 dB(A)"), which is also observed without noise exposure, and
  2. a noise-induced part, which is responsible for the deviation from the "75 dB(A)"-curve towards higher PTS.


The hearing impairment calculator may be used for the purpose of workers' protection. Commercial use is not permitted.


The hearing impairment calculator has been produced and tested applying a maximum of care. Nevertheless, DGUV cannot for whatever reason be made liable for accuracy of the results.


Dr Martin Liedtke

Division 4: Ergonomics, Physical environmental factors

Tel: +49 2241 231-2600
Fax: +49 2241 2234