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September 13, 2004

Earplugs vs. earmuffs

Study evaluates hearing protection in the workplace

BY GRANT CAMERON

STAFF WRITER

What’s better—earplugs or earmuffs?

Well, if you work in a place with low-frequency sounds, it might be wiser to use earplugs.

And if you work in a place with higher-frequency sounds, earmuffs are the answer.

Those were some of the findings, at least, in a study that examined whether hearing protection provided by earmuffs would be reduced by wearing them in combination with other devices such as hardhats, safety glasses and respirators.

The study was funded by the Workplace Safety and Insurance Board (WSIB) and sponsored by Mount Sinai Hospital in Toronto.

The principal investigator was Dr. Sharon Abel, formerly of Mount Sinai and now with Defence Research and Development Canada. Co-investigator was Andrea Sass- Korstak of the University of Toronto.

The results of the study were summed up recently in a report released by the Research Advisory Council of the WSIB, which highlighted a number of projects that have been completed over the last five years.

Seventy-two working age subjects (36 men and 36 women) were included in the study.

Two kinds of tests were performed on each subject. The ability to hear sounds was determined by measuring diffuse field hearing thresholds in quiet, and at eight different frequencies ranging from 0.25 kHz to 8.0 kHz. A second test measured the ability to discriminate consonants in quiet and in the presence of background noise.

The two tests were performed on each subject five times:

• With earmuffs mounted on a hardhat; ❑With earmuffs on the hardhat and with safety glasses;

• With earmuffs mounted on a hardhat and with a respirator;

• With earmuffs on the hardhat with both the glasses and respirator; and

• With no earmuffs, glasses or respirator.

The results showed that for each of the conditions, the noise reduction provided by earmuffs increases as frequency increases from 0.25 kHz to 1 kHz, after which there was no further increase.

The greatest noise reduction occurred with the muff on the hardhat alone, and the least noise reduction occurred with the muff on the hardhat used in combination with the safety glasses and the respirator.

The investigators concluded that wearing other protective safety gear around the head could interfere with the hearing protection provided by earmuffs.

The Advisory Council report says it has long been known that the protection against high-level noise provided by earmuffs generally falls short of manufacturers’ specifications.

However, what had not been studied previously is whether earmuff protection would be compromised further if the earmuffs were worn in combination with other devices.

Dr. Abel concluded that under all conditions Class A earmuffs protected workers best against higher frequency sounds. They were also more effective for men than women.

On the basis of the findings, Dr. Abel recommended that:

• Because earmuffs protect least against lower-frequency sounds, it may be better, in workplaces in which low-frequency sounds are the concern, to use earplugs instead of earmuffs, since plugs provide better low frequency protection than muffs and fit well regardless of other safety gear worn about the head.

• Attention should be paid to the sizing and fit of earmuffs, especially for women, whom protective devices tend to fit less well than men, and in situations in which muffs are worn in combination with other devices.

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