Investigation of intermittency in the noise exposure pattern of longwall coal miners

Abstract

It is generally recognized that intermittent exposures to noise are less hazardous than continuous exposures with the same energy. This effect has been accounted for in the USA with the use of a 5-dB exchange rate, instead of the 3-dB rate associated with the equal energy principle. However, the appropriateness of the 5-dB exchange rate for assessing the risk of noise exposures in mining has never been examined closely. The authors have previously reported the results of a worker noise exposure survey conducted at six longwall coal mines [R. C. Bartholomae and J. A. Burks, Proceedings: NOISE-CON ’94, 1017–1022 (1994)]; the time-resolved dosimeter data from that study were reanalyzed to determine if the noise exposure pattern of longwall miners can be categorized as intermittent. For this purpose effective quiet is defined to be a period of time in which the sound level is less than 75 dBA [W. Melnick, J. Acoust. Soc. Am. 90, 147–154 (1991)] for 10 s or longer [K. D. Kryter, The Effects of Noise of Man (1985), p. 273]. It is found that the miners experience an average of 125 periods of effective quiet and an average total quiet time of 1.7 h on a daily basis.