Signal audibility when wearing hearing protectors

Grafic: Car wearing hearing protection equipment

Public road transport vehicle drivers are subject to special hearing protection requirements
Source: DGUV(detail of title page of BIA Report 5/97)

Users of hearing protectors at workplaces may need to be able to hear signals from the work environment. The essential aspects for selection of a hearing protector suitable for this purpose are the audibility of warning signals and sounds containing information in the work environment, and the comprehension of speech at the workplace. The IFA list of approved products (list of all hearing protectors with EC type examination certificate reported to the IFA) assists in selection by stating supplementary codes indicating the signal audibility. The codes are determined by the IFA from the mean values for the sound attenuation measured during the type examination of the hearing protectors.

The significance of the codes is as follows:

  • W: The test criteria of "signal audibility (general)", "speech intelligibility", and "perception of informative operating sounds" are satisfied. The maximum mean increase in the mean values for the octave band sound attenuation is 3.6 dB/octave.
  • X: Hearing protector with an extremely flat attenuation curve. This is suitable for persons with impaired hearing, and may also be suitable for musicians. The maximum mean increase in the mean values for the octave band sound attenuation is 2 dB/octave. A flat attenuation curve means that the increase in sound attenuation from low to high frequencies is low. The greater the difference in sound attenuation in the different frequency ranges, the greater the change in perceived hearing compared to the unprotected ear. This can cause problems during demanding hearing tasks such as the recognition of signals or for particular groups of persons such as musicians. For this reason, a hearing protector with a frequency-independent sound attenuation characteristic (code W, or better still code X) should be selected in such cases.
  • S: Signals are audible during work on the permanent way.
  • V: Signals are audible for drivers of vehicles in public road traffic.
  • E1, E2 and E3: Signals are audible for engine drivers and shunters in railway operations in the following qualities: E1 = very suitable, E2 = suitable, E3 = partly suitable.

The codes W and X take account only of the sound attenuation values of the hearing protectors. Hearing protectors marked in this way are therefore suitable for the majority of workplaces. The three other codes, i.e. S, V and Ex (x = 1 to 3), also include the spectra of signals and background noises at the specific workplaces stated. In Germany, the responsible authorities impose particular requirements upon the signal audibility when hearing protectors are worn in these three areas of work. These requirements are met when a suitably marked hearing protector is selected and its suitability for use at the workplace can be demonstrated by means of a personal hearing test. Procedures for the hearing test can be found in the publications of the accident insurance institutions concerning the relevant areas of work.

The IFA has issued a series of publications on the special requirements in Germany concerning signal audibility when using hearing protectors. They have been gathered in a list (PDF, 180 kB) containing links to the abstracts and in some cases to the full texts.

A list of hearing protectors that are suitable for use in railway operation (engine drivers and engine driver/shunters) can be downloaded here.

A web application can be used to obtain a prognosis of the perceptibility of warning signals for a hearing protector (codes W, X, S, V and Ex in the IFA's list of approved products). The prognosis is based upon sound attenuation values from the type examination of the hearing protector.


Prognosis calculator

Contact

Dr Martin Liedtke

Division 4: Ergonomics, Physical environmental factors

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


Dr Sandra Dantscher

Division 4: Ergonomics, Physical environmental factors

Tel: +49 2241 231-2613
Fax: +49 2241 231-2234