Audiometric studies versus predictions of drastic deteriorations of hearing protectors' noise attenuation due to reduced wearing time: Misjudgments by standards based on the energy-equivalence principle.

Background: International standards based on the energy-equivalence principle predict a drastic deterioration of hearing protectors' noise attenuation if the protector is not worn for only brief time periods.

Objective: Therefore, studies in a laboratory setting were carried out to examine whether corresponding temporary threshold shifts (TTS) due to realistic noise exposures can be found.

Methods: Ten test subjects (Ss) were exposed to two reference exposures of 94 dB (A) for 1 h and 97 dB (A) for 1/2 h. Subsequently, they were exposed to noise of 106 dB (A) for 1/2 h on two additional days. With the exception of a 3 3/4 min-period, in these tests the Ss wore hearing protectors with noise attenuation of 20 dB and 30 dB, respectively. The resulting noise exposure was energetically identical to the reference exposures as well as to 85 dB (A)/8 h. If the equal-energy rule - which is used in the standards to predict the protection losses - is indeed valid, all 4 tests should result in almost identical threshold shifts.

Results: The experimental results do not confirm, but rather contradict the predicted drastic deterioration in attenuation. Particularly, the hearing protector with a noise attenuation of 30 dB performs much better in real-life situations than the theoretical assessment indicates.

Conlusions: With minimally reduced wearing time of hearing protectors the protection losses which are prognosticated by national and international standards are not associated. Instead, the energy equivalence principle applied in the standards leads to heavy misjudgments.