Understanding noise in the workplace

Noise-induced hearing loss (NIHL) is, needless to say, prevalent in loud work environments. Among those industries posing the highest risk for NIHL is the manufacturing industry.

Noise-induced hearing loss (NIHL) is, needless to say, prevalent in loud work environments. Among those industries posing the highest risk for NIHL is the manufacturing industry.

Metal stamping and grinding are among the activities most hazardous to process workers’ hearing health.

Metal stamping machines emit short, high-level noise at intervals, with quiet periods in between. This means operators tend not to wear ear protection because noise isn’t constant.

However, the noise levels in stamping plants typically reach between 100 to 110dB. It’s not uncommon for people working in these conditions to experience ringing in their ears at the end of a day.

Ringing is an indicator of damage to the microscopic hair cells or hearing nerves within the inner ear – once these cells die they never replenish. In other words, hearing damage is irreversible.

An exacerbating factor for the growing instances of work-related hearing damage is that it’s accumulative. Employees are often unaware that they are being affected until it’s too late.

It generally takes between six and ten years for someone suffering hearing loss to visit an audiologist, during which time they continue to expose themselves to harmful volumes.

Calculating how long it might take to contract NIHL in the workplace is not an exact science. Current guidelines assume a constant and invariable exposure to sound.

There are two main factors that go towards making noise harmful: volume and length of exposure.

Taking these into consideration, it is generally accepted that noise starts to become harmful at around 85 decibels (dB), which is equivalent to the noise from heavy traffic.

In Australia, NOHSC defines specific noise management guidelines for organisations within the following documents downloadable from the www.safeworkaustralia.gov.au website: National Standard for Occupational Noise; and National Code of Practice for Management and Protection of Hearing at Work.

Essentially in line with Europe, the national standard for exposure to noise in occupational environments in Australia is an average daily exposure level of 85dB.

This is based on scientific research revealing that exposure levels above 85dB represent an unacceptable risk to hearing. The longer the exposure the greater the risk, and for each 3dB increase the allowed exposure time is halved.

This means if you work in an environment where you are exposed to 100dB the allowed exposure time is 15 minutes.

Where to start?

A good practice for companies is annual audiograms to monitor employees within loud industrial environments for signs of hearing loss.

Current industry advice dictates that if an employee shows hearing loss of 10dB or more, that person must be informed and also required to wear ear protection at all times.

The primary problem with this approach is that it’s reactive, only working to prevent further hearing damage once a certain level of damage has already occurred.

A more effective approach is for employers to enforce the wearing of hearing protection as a preventative measure, providing all staff with earplugs or earmuffs.

However, unless hearing protection devices are both effective and convenient, they will simply be abandoned.

Many people assume that earmuffs block more sound than earplugs, but it’s more to do with achieving a good fit in the ear. An earmuff or plug with an NRR (Noise Reduction Rating) of 30 might in fact only reduce the sound impact on the ear by 20dB if not a good fit.

If specific fit data is not available, NIOSH (National Institute for Occupational Safety & Health) recommends de-rating hearing protectors by a factor that corresponds to the available real-world data, e.g:

* Earmuffs – Subtract 25% from the manufacturer’s labelled NRR;

* Formable earplugs – Subtract 50% from the manufacturer’s labelled NRR;

* Other earplugs – Subtract 70% from the manufacturers labelled NRR.

Repeated studies show that individual training is fundamental to the proper use of earplugs. Group training in earplug use tends to be ineffective, with workers using the plugs incorrectly afterwards, compared with the far more positive result of one-on-one training by a safety professional.

For earmuffs, comfort as well as fit is paramount. The key is to opt for adjustable, comfortable earmuffs – this can make all the difference between whether employees keep them on or not.

The ideal scenario is to find hearing protection capable of safeguarding the wearer’s hearing during times of high noise, without isolating them during quiet times.

One option is to use noise cancelling protectors that assess noise levels via a microphone positioned near to the ear, and generate an ‘anti-noise’ sound wave to reduce unwanted ambient noise.

However they work best for continuous sounds and are less effective against intermittent audio signals.

A safer option for effectively addressing sound attenuation and presenting the lowest inconvenience factor is the level-dependent earmuff or earplug device.

These relatively new innovations in hearing protection technology feature a number of tiny microphones feeding sound signals back to an amplifying circuit with a built-in limiter.

Speech patterns are picked out from general noise and elevated so that wearers experience crystal clarity in listening to conversation. All other noise is suppressed down to a safe level of 82dB.

This is especially valuable in a loud manufacturing environment, where process workers can be effectively protected from hearing damage without being isolated from verbal instructions and general communication.

*Justin Miller is CEO of Sensear, 08 9277 7332, www.sensear.com

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