A Cochrane review [Abstract] 1 included 6 studies with a total of 169 subjects. The effect of hearing protection to noise exposure of workers was studied. Personal hearing protection reduced noise exposure significantly. Hearing protection from various manufacturers showed an immediate effect of noise attenuation of around 20 dB at frequencies 0.5 kHz to 8 kHz under field conditions. However, noise attenuation ratings of hearing protection under field conditions were consistently lower than the ratings provided by the manufacturers. One high quality study showed that if workers got proper instructions in the use of earplugs, the hearing protection was larger.
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