Testing procedure for communication ear plugs

Status:

completed 12/2010

Aims:

In accordance with Directive 89/686/EEC, hearing protectors constitute Category II personal protective equipment, and must pass an EU type examination. This examination is conducted by an independent body ("notified body") such as the Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA). Harmonized test standards or recognized test procedures are employed for this purpose. Before now, a test procedure did not exist for communication ear plugs. Manufacturers have now developed prototypes and applied to the IFA for testing. Various proposals exist for the testing of products of this kind. Experience has however not yet been gained with testing. Since the integral speakers in these products generate sound of their own which, at high levels, could damage the hearing, a suitable test is indispensable for their safe use.

Activities/Methods:

A standard (EN 352-7) for the testing of ear plugs with level-dependent attenuation already exists; it has so far failed to meet with acceptance, however. From an acoustic perspective, the test arrangement used in the standard is only a compromise for the testing of ear plugs with level-dependent attenuation. The arrangement in EN 352-7 could however be used for the testing of communication ear plugs. Owing to the simpler test conditions of other test arrangements (couplers), such as the KEMAR test system (with the IEC 711 coupler), it was however anticipated that these arrangements would be even more suitable for the test procedure which is to be developed. The project was to examine the suitability of a number of test arrangements. The experience gained in the process was also useful in resolving the issues associated with the procedure set out in EN 352-7.

Results:

A number of test arrangements, i.e. artificial heads with test ears, were compared. In addition, tests were performed on test persons: in these tests, the noise level produced by an ear plug with communication facility was measured by means of a small microphone in the ear canal. Comparison of the results with those from measurements performed on the artificial head revealed that on a random sample of test persons, the ear simulator (coupler) in accordance with IEC 711 reproduces the average noise level in the ear canal faithfully. A new artificial head was procured which combines a coupler in accordance with IEC 711 with adequate inherent noise damping and can therefore also be used to test ear plugs with level-dependent damping to EN 352-7.
Testing of communication ear plugs should be based closely upon the procedure employed for the testing of ear-muffs with electrical audio input described in EN 352-6. In this procedure, eight test samples are each measured twice on the artificial head, resulting in values for 16 ears (eight test persons), from which the mean value and standard deviation are then calculated.
In addition to these measured values, however, consideration must be given to the scatter in the noise level which results from the differences in wearers' anatomy (i.e. the geometry and dimensions of the ear canal). For this purpose, the relevant values for various products were measured in the ear canal by means of microphones. As expected, the scatter in this case is considerably greater than that measured on the artificial head, and replaces the latter for further analysis. A reliable estimation of the resulting noise exposure can therefore be anticipated.
The test procedure is to be harmonized at European level with the other test bodies in order to assure a uniform procedure.

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