Exposure to Steady‐State Noise and Impairment of Hearing

A damage risk criterion for exposure to noise is specified primarily in terms of the impairment of speech communication as the result of noise‐induced deafness. The criterion allows as permissible any noise exposure that, on the average, causes a temporary threshold shift measured 2 min after exposure, in the average normal ear, of no more than 10 dB at 1000 cps or below; 15 dB at 2000 cps; or 20 dB at 3000 cps or above. It is held that after 10 years of near daily exposure to such a noise, the average person will have a stable hearing level, relative to present‐day audiometric zero, of a similar magnitude. To determine what kinds of sounds and durations of exposure would meet this criterion, twelve ears were exposed to bands of filtered, random noise for durations ranging from 3 min to 8 h. Temporary threshold shifts for pure tones were obtained by comparing pre‐ and post‐exposure audiograms. From these data functions were obtained which show the sound‐pressure level, durations, bandwidth, and center fre...