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Making assumptions can be dangerous!

Published:  10 September, 2014

Unfortunately, despite increasing levels of regulation aimed at safeguarding workers against hazards, some persistent bad assumptions still remain in place – particularly when it comes to noise risks and hearing conservation. Left unchecked, these assumptions can undermine all the good work of an otherwise healthy hearing conservation programme and leave the door open for hearing loss.

Assumption 1: Hearing protection is self-explanatory.

On the surface hearing protection may seem an intuitive thing – you just put it in or over your ears. As a result, one of the most common assumptions is that people know how to use hearing protection and basic training is therefore overlooked. Worse still it can be wrongly assumed that workers will read the manufacturer’s instructions on the packaging.

However, a comprehensive study of hearing conservation programmes (HCPs) in the United Kingdom revealed that when hearing conservation training had been provided by posters or leaflets, less than half of the “trained” workers could recall the content. But 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.

When it comes to properly fitting foam ear plugs a simple three-step process can be promoted to great effect: Roll, Pull, and Hold. Roll down a foam earplug into a small crease-free cylinder, pull the outer ear up and back to open the ear canal, insert the earplug and hold in place while it expands.

For proper fit of earmuffs, hair should be moved aside, and the earmuff seated so that it encloses the entire ear. Safety glasses with thick temple bars at the frames should be avoided, however, safety eyewear or prescription glasses with a thin frame cause no significant decline in attenuation. Safety eyewear with wider frames can cause noticeable gaps in the cushion seal, resulting in a potential attenuation loss of 5-10 dB and so should not be used.

Assumption 2: Any earplug in the ear is blocking some noise. It simply isn’t true. An earplug just sitting in the bowl of the outer ear, without sealing the ear canal, is simply nice ear decor — offering little protection from noise. In fact, attenuation measurements show that poorly-fit earplugs often create a resonance cavity in the ear canal, actually increasing the noise level by a few decibels (similar to cupping your hand around your ear to hear better).

This can be a major problem for a safety manager who is trying to judge compliance visually. He/she might assume that any earplug that can be seen in a worker’s ear must be doing some good, and focus more on the workers who are wearing no protection at all. In reality, a poorly-fit earplug offers no protection so training from the outset to ensure proper fitting takes place is essential, as is regular compliance monitoring.

One visual cue of a properly fitting earplug is that it is hardly visible when looking in a mirror straight ahead, or when looking at a co-worker face-to-face. A poorly-fit earplug on the other hand is clearly visible protruding from the ear canal.

For the user, a good self-test of proper fitting earplugs is easily performed. Prior to inserting the earplugs, they should press the palms of their hands tightly against their ears, and say some words out loud. Their own voice sounds louder and deeper when their ears are covered. Now they should insert the earplugs, and repeat that voice check. If the earplugs are properly fitted, there will be very little difference in the sound of their voice when they cover and uncover their ears with their hands.

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

It seems plausible that if a well-fitted earplug blocks 30 dB of noise, then a half-fitted earplug must block 15 dB of noise. Unfortunately hearing protection doesn’t work that way. Instead, a half-fitted earplug is often providing 0 dB of attenuation.

However, a properly fitted earplug can sometimes make the worker feel isolated — unable to hear warning signals, co-workers, machine maintenance sounds, or communication radios. Where this is the case some workers opt to remove their earplugs to 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.

In a series of research studies designed to find out why workers do not use their earplugs more consistently, the National Institute for Occupational Safety and Health (NIOSH) in the US reports that the predominant reasons are inability to communicate and interference with job performance. The ideal hearing protector should not block all sound (overprotection), but rather reduce hazardous noise levels while still allowing a worker to hear the sounds that are critical to the job: co-workers, warning signals and equipment maintenance sounds.

While there is no magic valve in hearing protectors that lets ‘good’ sounds in and keeps ‘bad’ sounds out, there are some hearing protectors that are more speech-friendly than others. These uniform attenuation hearing protectors attenuate all frequencies fairly equally, meaning speech and warning signals will sound more natural, rather than inaudible or distorted. Many users of uniform attenuation earplugs, for example, report they can still hear what they need to hear for their job performance.

Assumption 4. Cut the SNR in half to predict real-world protection. Many studies have shown that attenuation achieved in the real-world is sometimes far below the laboratory Single Number Rating (SNR). 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.

A study carried out - by the hearing conservation team at Honeywell Safety Products using a fit-testing system for earplugs, saw them visit eight industrial sites, measuring real world attenuation of 100 workers using earplugs from a variety of manufacturers.

Workers were instructed to fit their earplugs as they would usually. A Personal Attenuation Rating (PAR) was then measured on each ear. The PAR results showed that one-third of the workers achieved attenuation slightly higher than the published SNR, one-third of workers showed attenuation within 5 dB below the published SNR, and about one-third showed significantly lower attenuation (anywhere from 0 to 25 dB).

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

There are several methods of measuring real-world attenuation on workers wearing earplugs. Instead of relying upon the population estimates of the SNR, the latest testing methods enable safety managers to measure each worker’s individual protection level. Employees are given a special listening test without their earplugs, and then with them in. The difference in the results indicates how much protection is being offered by the earplugs. The safety manager can then ascertain whether more training is required on how to fit the earplugs or whether a different earplug should be tried. In a field study of real-world fit, many workers received 20-30 decibels more protection simply by trying a different earplug.

By using these latest earplug fit testing methods to verify an individual’s attenuation, a safety manager can document exactly how much protection a worker receives with a given earplug. The result is a Personal Attenuation Rating (PAR).

Assumption 6. There’s no way to measure the noise dose of a worker under the hearing protectors throughout their workday.

Noise dosimetry is typically measured by clipping a microphone on the collar of a noise-exposed worker. The dosimeter samples the noise levels throughout the day, and accurately gives a reading at end of shift showing the noise dose of the worker for that day. A dose over 100% exceeds the permissible exposure Limit of 87 dB outlined in EU Directive 2003/10/EC. But such ambient dosimetry measurements tell us nothing about the noise level reaching the eardrum under the hearing protectors.

Ideally, the best way to know if a worker is protected from hazardous noise therefore is to use in-ear dosimetry technology. This uses miniature microphones, inserted under the earplug or earmuff, to measure the noise dose at the eardrum. If a worker has properly fitting hearing protectors, the noise dose will be safe — under 50% for the work shift. But if the worker has an inadequate fit, or removes the protectors repeatedly during high noise, the resulting noise dose at the end of the shift will be excessive. This immediate feedback gives the worker (and safety manager) the critical information to make immediate corrections.

In a typical hearing conservation programme, it takes several years of audiometric testing to ascertain whether a worker has lost hearing due to workplace noise. But by using in-ear dosimetry, any worker can know immediately and precisely whether hazardous noise levels are reaching their eardrum. Stop the noise exposure at the eardrum, and you stop the hearing loss.

Bad assumptions sink many well-intentioned safety initiatives. But avoiding these simple bad assumptions about hearing protection will help a hearing conservation programme stay on solid ground, and do just what it is designed to do: prevent noise-induced hearing loss.

For further information please visit: www.honeywellsafety.com