The effectiveness of hearing protectors in practice.
A series of workmen being evaluated for pensions for occupational hearing loss were asked to bring their own hearing protectors from work, to fit them themselves, following which attenuation studies were made. The muffs and most earplugs produced similar attenuation levels at high frequencies, although the muffs produced less attenuation at low frequencies. In all cases the mean attenuation was significantly lower than optimum figures suggested in the literature, and the standard deviation was relatively high. Personally molded earplugs were significantly less effective than other plugs used. Reasons are discussed for the relatively poor performance of these devices and the concept of assumed protection, i.e. mean minus one standard deviation, is discussed. There is need for better instruction on how to use hearing protectors if they are to be effective.