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.
