Intermittent-noise effects and hygienic standards.

Effects of variable equivalent intermittent noises on hearing acuity, peripheral vascular tonus and the latent period of motor responses were studied experimentally. Two-hour exposure to noise in the form of noise intervals of rectangular shape alternating with pause intervals at ratios of 20 :5, 20 :20, 20 :30, 10 :20 and 30 :60 seconds or to nonfluctuating noise was used. In all instances the equivalent level of noise was 80 dB(A). It was found that the degree of biological effect depended on the summary duration of the noise intervals in the total exposure period. A formula for correcting noise-level safety standards in the case of intermittent noises was proposed, viz: (formula; see text) where tau = summary duration of noise intervals and T = exposure time under evaluation. The possibility of using this relation also in evaluating situations where complementary to the equivalent level also the peak level of a given noise is subject to standardization is discussed.