Hearing protectors: correction values bridge the gap between laboratory testing and the field

Hearing protectors frequently attain lower sound-attenuation levels in industrial use than in the type test performed in accordance with the standard. This has been demonstrated by a study conducted by the BGIA Institute for Occupational Safety and Health of the DGUV (BGIA Report 4/2009, “Schalldämmung von Gehörschützern in der betrieblichen Praxis – Studie von 2005 bis 2007“). Correction values for the sound-attenuation values measured in the laboratory are intended to support the user in the fi eld in selecting hearing protector products. Standards may also provide assistance in reducing the discrepancy between the laboratory and the field.

The EU Personal Protective Equipment Directive, 89/686/EEC, requires that prior to hearing protectors being placed upon the market, an independent third party (notified body) must test whether they satisfy the essential health and safety requirements of the directive. In a laboratory measurement, the sound-attenuation values which can be attained under standardized ideal conditions are determined for each product. The manufacturer is obliged to indicate the measured sound-attenuation values on the packaging. These provide the user with a basis for selecting hearing protectors suitable for the noise situation concerned, and thus for observance of the maximum permissible exposure values stated by the 2003/10/EC EU Noise Directive.

In the fi eld, however, the sound attenuation is generally substantially lower than that measured in the laboratory. The following technical aspects may influence the protective action:

• Ageing or storage (earplugs are no longer suffi ciently fl exible to adjust to the ear canal; the sealing cushions of ear muffs may be indented or the headband bent)
• Problems with use together with other forms of PPE (helmets, goggles, etc.)
• Absence of marking (confusion of left and right)

A further essential cause is the incorrect use of the PPE (incorrect size or wearing position; errors when inserting the earplugs). The physical characteristics of the user may also be a factor (e.g. very dense hair; the particular geometry of the wearer‘s ear canal).

In order to ensure that the maximum permissible exposure values are observed, users require reliable information on sound attenuation. For this reason, the BGIA, in conjunction with several BGs (institutions for statutory accident insurance and prevention), measured the sound attenuation of the hearing protectors used in a range of industrial areas under the wear conditions encountered there. Over 800 data records were obtained for over 20 models. The measurement method was based as far as possible upon the laboratory type test to ISO 4869-1: “Acoustics; hearing protectors; subjective method for the measurement of sound attenuation“.

The study shows that the deviations between the values measured in the laboratory Hearing protectors: correction values bridge the gap between laboratory testing and the field SPECIAL and in the field vary according to the hearing protector type. The greatest deviation, of almost 8 dB, was observed with earplugs which must be shaped prior to use. Pre-shaped earplugs for example exhibited a substantially lower deviation; the mean value in this case was 4.4 dB.

Based upon the results of the study, the “Personal protective equipment“ expert committee defined concrete reductions for each hearing protector type by which the sound-attenuation values stated by the manufacturer can be adjusted for practical application. The correction values have already been adopted in publications issued by the accident insurance institutions (BG Rule 194, BG Information 5024 and 8621).

Approaches in standardization

Test codes have the function of making different products comparable by means of standardized test conditions. Deviations between the test conditions and those in industrial use are unavoidable, but are to be reduced to a minimum by test conditions for hearing protectors which most closely resemble the conditions in practice. It is important for users to be adequately informed of the issue.

The technical causes of the deviations which have been detected are to be eliminated primarily by suitable provisions in product standards. The standards are to be extended to cover aspects such as deterioration in the protective action as a result of ageing or storage (See also KAN Report 39 "Consideration of time-related performance characteristics of PPE in standards (pdf)), and are to require appropriate marking of the products. In addition, requirements governing the information for use to be provided by the manufacturer are to ensure that the user receives adequate information on proper use of the hearing protectors. This information could also indicate that the sound-attenuating effect stated was measured under laboratory conditions, and may be lower in practice.

 Dr. Sandra Dantscher
sandra.dantscher@dguv.de