Noise In Many N.Z. Factories “Deafening”

Press, Volume CII, Issue 30126, 9 May 1963, Page 20

Noise In Many N.Z. Factories “Deafening”

The noise level in many New Zealand factories is such that many workers become deafened. After 15 to 20 years in the factories, they rely mainly on lipreading. Mr M. Rodda, of the applied psychology unit of the University of Canterbury, said this yesterday when asked to enlarge on an article which he and his coworkers, Messrs L. J. Smith and G. D. Wilson, wrote for the “New Zealand Medical Journal.”

‘ ‘These factory workers often do not realise they are lip-reading, but if they cannot see one’s lips they just cannot hear,” said Mr Rodda. “Something should be done to improve the position,” he said. “The noise should be cut down at its source, or the workers should be given ear-plugs or ear-muffs to protect their hearing. Both measures can be used.”

Ear-plugs were often satisfactory provided they were fitted satisfactorily to start with, and provided the workers Were instructed properly

in their use, Mr Rodda said. Advice on how to cut down noise at its source could be obtained from an acoustic engineer.

The results of a survey of most of the workers in two Canterbury weaving mills, reported in the “Medical Journal,” indicated that for the average worker of more than 15 years’ service the loss in the higher speech frequencies was such that the aural nerves were affected as well as the conducting apparatus of the ear, Mr Rodda said. “And I have reason to believe, from confidential information, that many other factories in this city and elsewhere in New Zealand have a noise level as high as or higher than in the factories where we took our tests,” he added. The average noise levels in the working areas of the two mills were, respectively, about 109 and 107 decibels. The maximum recommended by the Health Department is about 85 decibels, the exact level depending on the frequency.

The tests showed that the average worker with from 15 to 20 years’ service in the mills had a hearing-loss of about 70 decibels at 4000 cycles a second, with a 40decibel loss at 1000 cycles, 55 decibels at 2000 cycles, 65 decibels at 3000 cycles, and 45 decibels loss at 6000 cycles. The range 1000 to 4000 cycles represented the important speech frequencies. For comparison, it was routine for a person with a 30-decibel loss to be considered for a hearing-aid, while anyone with a loss of more than 60 decibels was reckoned very hard of hearing. Sixty decibels represented about the maximum of conducting

loss; anything above this indicated nerve-deafness, which could not usually be rectified by a hearing-aid. “When nerve-deafness is present, there is a loss not only of hearing but of ability to discriminate between sounds. A person who is nerve-deaf presumably hears just a jumble which doesn't make sense,” Mr Rodda explained. The experiments in the two Christchurch factories indicated that the average hearing loss at the lower range of frequencies was considerably less than in the 1000 to 4000 cycle range. Asked if this meant that the effects of the high-range loss might be mitigated to a large extent by compensation from the lower range, Mr Rodda said he did not think so. because what was lost in the upper range was discrimination as well as amplitude. Workers with more than 25 years’ service in the mills tended to have a smaller loss in the speech-frequency range than those with shorter service. Mr Rodda and his co-authors suggest this was because workers susceptible to a greater loss in the speech-range tended to find the noise unbearable and eventually changed their occupations.