Document DDZx30dg8KzqbB7ORm9vOgxaQ

1967 National Safety Congress reactions to noise, because it is known that the accumulative efforts of prolonged expo sure are physiologically dangerous, through loss of sensitivity to toDCS, through deteriora tion of tho hearing function of tlio inner car, and oventually through permanont nudiometric damage. Psychological factors ajro also involved. Certainly, noise serves to distract and rcduco the effectiveness of a worker and de crease his output. Intermittent noiso is tho most obnoxious, particularly during any pe riod of adjustment to a now task or in new surroundings. Evidence indicates that, if a worker remains in a noisy situation which distracts him initially, he may eventually adapt to it, and regain his original loss of output. While this may bo so, the fact is often wrongly interpreted to mean that, in the long run, continued exposure to noise docs not have nny adverse effects. Such a generalization is definitely unjustified. Somo investigators hnvo found that tire ef fect of noise on work output depends upon the nature of the work; a long term job re quiring constant vigilance is especially sus ceptible. The effect of noise is more likely to be a higher rate of errors and accidents rather than on actual reduction in total out put. The attention of the worker wanders from the job in hand more often as tho noise level increases. Further, noise is more likely to lead to increased errors and accidents if its value exceeds 00 db., and high frequency audible noise is mono harmful in this respect than low frequency noise. Nolso and its effects have given riso to much controversy in industry. How danger ous can it be? Has it a deleterious effect upon worker performance? Does it effect certain types of work more than others? Has it a detrimental effect upon worker adjust ment? The intensity noise level is probably the most important single factor in determining the severity of exposure, but tho duration of exposure is also important Tho threshold level of noise that tho ear can withstand for some time without audiometric damage is of the order of 60 db. Since the average pneu matic percussive rock drill produces some 120-130 db., the problem is not one to be brushed aside lightly. Tho underground mining environment has become progressively so noisy that speech communication in a confined area is difficult if not impossible and, for this reason, speech interference levols arc evaluations of impor tance. Tho consonants contain most of the informative vnlucs in speech but unfortu nately thoy nro more readily masked than vowels bccauso tho consonant sounds are weaker. Noiso may therefore mask certain speech sounds nnd not others. Tho energy of tho vnrlous speech sounds is distributed over tho frequency rango of below 100 to above 10,000 c.p.s. The "s" in speech has an en ergy rango of from 4,000-8,000 c.p.s.; in contrast, most of tho "cc" in speech is dis tributed below 4000 c.p.s. Such variations in sound frequencies account for failure of speech communication in noisy environ ments. Insofar os industrial noiso is generally un pleasant, it may be assumed that its correc tion will lead to better worker morale for the same reason that any consideration for tho welfare of employees tends to produce a fnvorablo .reaction. Intermittent, high pitch, and high intensity noises ore the most dis turbing so far os emotional reactions are con cerned. Some individuals are hypersensitive to noise nnd cannot make effective adjust ment. Ear defenders will invariably serve a use ful purpose, but it is difficult always to "sell" the principle. Personalized car plugs, cast for individual cars, arc probably moro readily acceptable. Tho use of mufflers and machine enclosures have proved partially cffcctivo in reducing noise levels in practico, but the noiso surrounding evon the muffled rock drill is still dangerously high. The greatest advan tage in relation to rock drill noise abatement will probably be made through improved de sign of the equipment and the application of human factors engineering. In every mine, some staff member should be responsible for the noise hazard. He should be equipped with noise and peak level meters, an octave band nnolyzcr, and other standard equipment and he should be trained in their use and in interpreting their data. Periodical noise surveys should be car ried out nnd steps taken to mitigate this nui sance to personnel, impediment to produc tion and menace to health. In many cases, simple remedial steps are effective: others present topics for research. Of particular in terest, and something we know little about, is the influence of reverberation upon noiso levels hem machines and .at the operator's ear; this is of importance in development ends, rises and other headings. 10