Attenuation of ear muffs in Canadian mines

CIM Bulletin, Vol. 72, No. 812, 1979

M.U. SAVICH, Research Scientist, Elliot Lake Laboratory, Mining Research Laboratories, CANMET, Energy, Mines and Resources Canada, Elliot Lake, Ontario

In Canadian mines, ear muffs are now an essential part of safety equipment. Because of this, a research study was conducted to investigate their efficiency. The main characteristics of eleven commercially available ear muffs were investigated in the laboratory and analyzed by: (1) a psychophysical method; and (2) a physical method. These investigations showed the following effects:head size has a significant influence on the attenuation because of a different clamping force;the amount of hair trapped between the ear muff cushion and the head decreased ear muff attenuation; attenuation and comfort are not in a causal relationship;with the use of glasses and their adapters, attenuation decreases—the adapters are not effective sound barriers;there are no great differences in attenuation with neck movement; the efficiencies of various brands of ear muffs are not equal; ear muffs with a small cushion area start serving   their purpose   more   quickly because the force per unit area is larger; a clamping force larger than 900 g wt, in most ear muffs, does not cause an increase in attenuation; attenuation   characteristics   (ANSI Z24.22 - 1957) of ear muffs show some correlation with physical tests.Nine ear muffs out of the eleven were tested under uniform conditions in mines. Three ear muffs were found to be the best. All three ear muffs have bands passing behind the head. The ear muff with a support strap, which improves comfort and maintains a good fit during wear, showed the best attenuation. Causes of poor attenuation are numerous: bad mounting of ear muffs on helmets, improper fitting, interferen-cy by hair and glasses, improper wearing by miners, unsatisfactory enforcement by supervisory personnel, incomplete training of miners, etc.Results of this research have indicated that none of the ear muffs tested in this study contain all of the characteristics desirable in an ideal unit.Because of unsatisfactory ear muff attenuation in working conditions (15 dBA), it should be a mandatory requirement that workers wear both ear muffs and ear plugs if the noise level is higher than 105 dBA (various literature recommends 110 dBA).The key to the solution lies in the following:the foreman must be capable of helping and controlling miners in their task of wearing ear muffs properly; the program  must be  introduced to miners; and constant contact must be maintained with manufacturers.
Keywords: Underground mining, Ear muffs, Safety, Mine safety, Noise control, Attenuation.