Document MooBnrnKRx2Xjm7RpQQaRQmXa

INDUSTRIAL NOISE sure time are continuous Continuous ex posure should not produce the same effect as when the exposure is interrupted by rest periods For example, the effects to the ear of four hours of continuous exposure to 110 db are considerably different than those from eight hours of exposure to the same level with varied rest periods between the exposure periods, even though the total en ergy may be the same in both cases The ear that has had a chance to rest between exposures is probably more resistant to per manent loss than the ear that has been ex posed continuously without intermittent rest periods Effects of noise-exposure At first glance the problem of evaluating the effects of noise-exposure may appear to be deceptively simple Measurements of noise are fairly standard physical measure ments, lengths of exposure periods can be read from a clock, and the biologic effects of noise on man can be measured But-- which of the myriad noise-exposures should we measure? Which methods of measure ment should be used? Which of the many effects of noise-exposure do we wish to evaluate? Which parameters of noise-ex posure are responsible for which biologic effects? In what order of importance to the community and to the individual should these biologic effects be studied? Thus an evaluation of the effects of noise-exposure involves many arbitrary decisions and pre supposes the existence of information, often m fact nonexistent, about many related is sues Although ultimately safety men would like to be able to predict and control the effects of any noise-exposure on any indi vidual or group of individuals, the chance of being able to do so is very small, not so much because of the difficulty of measuring noise-exposure, but because of the wide variation of human responses to noise While the measurement of intermittent and irregular noise-exposure does pose some dif ficult problems, once techniques of measure ment have been developed, they probabfy can be measured with reasonable accuracy There is not as much optimism about measuring the effects of noise-exposure. In dividual responses to noise-exposure are highly variable, and measurement of these individual responses necessarily encompasses a wide range of values There are many causes of tlus variability including, among others, individual differences in susceptibili ty to noise-induced hearing loss, differences m total tame spent in industrial work, fre quent changes of type of occupation, nonoccupabonal disease, and nonoccupationallyinduced changes in hearing that accompany advancing age. There are so many different possible in dividual responses to a given noise-expo sure, that all that can be said with certainty is what responses will occur on the overage. The concept of a statistical average implies the existence of persons whose responses are not average and whose behavior, there fore, may differ widely from that of the average group This means that damage risk criteria correction factors for nonoccupational hearing loss that accompanies age (so-called "presbycusis corrections") or rating scales for establishing compensation payments that will "fit" everyone cannot be established whenever it is necessary to set standards for any effects of noise-exposure, these standards will be determined from the average response and not from the individual response In spite of the many difficulties that beset the study of the effects of noise-exposure on man some headway is being made. With the urgent need for a solution to many of the problems caused by noise, further ad vances should be forthcoming in the im mediate future The known effects of noise-exposure are of two types nonauditory effects which cause interference with communication by speech or which otherwise influence be haviour and auditory effects which consist of temporary hearing loss and permanent hearing loss Consider first the nonauditory effects of noise-exposure. Nonauditory effects Speech interference Perhaps the best understood nonauditory effect is speech in terference Noises that are not intense enough to cause a hearing loss may inter fere seriously with communication by speech. In checking a noise the average of the sound pressure levels in three octave bands, 300 to 600, 600 to 1,200 and 1,200 to 2,400 c, is a good indicator of the amount of interference that noise will have on 43-10