Manufacturing News

Bad assumptions about hearing protection

Here are five of the most common bad assumptions about hearing protection for noise-exposed workers. Ben Elsey* reports.

WE’VE all heard the old saying about assumptions, but in the world of personal protective equipment, bad assumptions can also be hazardous and often injurious.

Perpetually unchecked, these assumptions can hamper otherwise healthy Hearing Conservation Programs [HCP] and leave the door open for further occupational hearing loss.

Assumption 1: Hearing protection is self-explanatory.

Assuming that proper use of hearing protection is fairly intuitive, many safety managers provide little or no training in how to use protection properly. Or they generously assume that workers will read the manufacturer’s instructions on the packaging.

A comprehensive study of HCPs in the UK revealed that when hearing conservation training had been provided by posters or leaflets, fewer than half of the “trained” workers could recall the content.

Repeated studies show that the most effective use of hearing protection comes after one-on-one training. Large group training in hearing protection seems to have little effect on proper usage; only individual training can be linked to high attenuation results.

Assumption 2: Any earplug in the ear is blocking some noise.

It simply isn’t true. An earplug just sitting in the outer ear, without sealing the ear canal, may appear to be used properly. However, it offers little protection from noise. In fact, attenuation measurements show that a poorly fit earplug often creates a resonance cavity in the ear canal that actually increases the noise level – amplification – by a few decibels (similar to cupping your hand around your ear to hear better).

For a safety manager who is trying to judge compliance visually, a poorly fit earplug is clearly visible protruding from the ear canal when viewed from the front, while a properly fit earplug is hardly visible.

A simple self-test for proper fit is to insert the earplugs and walk into a noisy area. With the earplugs fitted, tightly place your hand over your ears, then release. If the earplugs are properly fit, there will be very little difference in the sound of the noise when your ears are covered or uncovered.

Assumption 3: An earplug halfway in the ear blocks about half the noise.

It seems reasonable that if a well-fit earplug blocks 26dB of noise, then a half-fit earplug must block 13dB of noise. Unfortunately, the math of hearing protection does not work that way. Instead, a half-fit earplug is often providing 0dB of attenuation.

Workers in noise levels of 85-95dB are routinely offered earplugs with Class 4 or 5 designation. When worn properly, the attenuation of such hearing protectors can isolate the worker-unable to hear co-workers, warning signals, machine sounds, or important announcements – and put them at further risk.

Workers often compromise their protection for improved communication by removing their earplugs about halfway, assuming they are still adequately protected. But in noise attenuation, any small channel or leak allows the noise to enter, and the protection quickly deteriorates from ‘all’ to ‘none’. Using a properly fitted, uniform-attenuating earplug will provide protection without sacrificing communication ability.

Assumption 4. To predict real world protection, de-rate the published attenuation to half its value.

Many studies have shown that attenuation achieved in the real world can often be very different from the laboratory-based, SLC80 decibel rating for earplugs.

There are a number of good reasons for this difference: users in the real world might not receive proper training, or might adjust their hearing protectors for comfort rather than protection, or they may intentionally compromise the fit in order to hear co-workers and machine noises more clearly.

To compensate, some have promoted a 50% de-rating method to try to predict real world protection for workers in a Hearing Conservation Program. Such de-rating is arbitrary and usually wrong!

Using a fit-testing system for earplugs, the Howard Leight acoustical laboratory visited eight industrial sites and measured real world attenuation of 100 workers using earplugs from a variety of manufacturers.

The results showed that one-third of the workers achieved attenuation slightly higher than the published SLC80 decibel rating, one-third showed attenuation within 5dB below the published Class, and only about one-third showed significantly lower attenuation (anywhere from 0 to 25dB).

Assumption 5. There’s no way to measure real attenuation on a worker wearing earplugs.

There definitely are several methods of measuring real world attenuation on workers wearing earplugs. Instead of relying upon the population estimates of the SLC80 Class system, a safety manager can now use a fit-testing system like VeriPRO to document exactly how much protection a worker receives with a given earplug.

While fit-testing may not be feasible to administer on every noise-exposed worker in the facility, it is certainly feasible for new hires or workers demonstrating a degradation in hearing levels, as documented in audiometric testing. These workers need to be retrained and refit with appropriate hearing protection, and the fit-test systems available now allow employers to accomplish that very effectively.

Bad assumptions sink many well-intentioned safety initiatives. Avoiding bad assumptions can help a HCP stay on solid ground and do just what it is designed to do: prevent noise-induced hearing loss.

*Ben Elsey is hearing conservation specialist with Sperian Protection Australia 1300 139 166, www.sperianprotection.com.au.

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