KANBrief 4/24
ISO 1999, Acoustics – Estimation of noise-induced hearing loss, last amended in 2013, is currently undergoing revision. Since some of the proposed amendments are not scientifically correct, KAN has commented on the revised draft.
ISO 1999 describes a mathematical model that can be used to calculate the anticipated hearing loss in persons who are exposed to noise and those who are not. The model requires knowledge of age-related hearing loss in groups of persons not exposed to noise, and of hearing loss in comparable groups of persons who have been exposed to noise and have never used hearing protection. These values were determined statistically for the model from a number of studies. Up to and including the current version of ISO 1999, published in 2013, the model drew upon hearing loss data for groups of persons not exposed to noise from ISO 7029:1984, Acoustics – Threshold of hearing by air conduction as a function of age and sex for otologically normal persons. This standard is based on data in a number of published studies, which was thoroughly reviewed. By use of this study data, ISO 1999 was able, almost 35 years ago, to describe the effect solely due to noise in the model, thereby enabling it also to be predicted for groups exposed to noise.
During the current revision of ISO 1999, reference was made to data from only two studies for the age-related hearing loss. In KAN’s view, however, this data is unsuitable: the new model is based on a natural hearing loss for groups of persons not exposed to noise that is lower than that assumed in the past. The calculation described in the new ISO 1999 draft standard thus results in the estimated effect of noise upon human hearing in groups of persons exposed to noise being higher than that estimated by the current model. According to the new estimation, groups exposed over many years to noise at 80 dB would undergo additional hearing loss. Other studies, however, have shown that noise at or below 80 dB(A) does not lead to any perceptible shift in the hearing threshold, even after many years’ exposure.
Above certain exposure limits and action values, employers are required to take protective measures. When determining these values for European Directive 2003/10/EC regarding the exposure of workers to the risks arising from physical agents (noise), the European Commission drew upon the 1990 version of ISO 1999. If the current draft were to be published as a standard and subsequently considered during a revision of the directive, this could result in the exposure limit values and action values being lowered significantly. At present, a mean daily noise exposure level of 85 dB triggers a requirement for protective measures for employees. The new draft standard would require protective measures to be taken at values as low as 77 dB, even though no validated scientific evidence exists for this requirement. Under certain circumstances, this value may be exceeded even during use of a vacuum cleaner, or in an aircraft cabin. Should no other measures be possible, employees would then have to wear hearing protectors.
Lowering of the values could therefore lead to protective measures being taken that from a scientific perspective are unnecessary. This has repercussions for several parties involved:
Employers must assess the hazards to workers at work and determine suitable measures. Measures must be reasonable, necessary and proportionate. The changes to the standard would result in the measures no longer satisfying this principle.
In summer 2024, KAN submitted a comment to DIN opposing the current draft of ISO 1999. In September 2024, the national mirror committee opposed the current draft of the standard, and DIN voted at ISO accordingly. The result of the ISO vote was that the present draft was rejected. However, discussions at international level are still in progress and it remains to be seen whether, and if so in what form, a revised draft will be published.
Dr Anna Dammann
dammann@kan.de