Occupational noise

Any loud sound, whether from music, firearms or tools and machinery can damage hearing, particularly if exposure occurs regularly. The risk of hearing loss from noise—noise-induced hearing loss (NIHL)—is high for mine workers as a lot of mining equipment is large and noisy. Long work shifts result in prolonged noise exposure with insufficient time for sensitive parts of the ear to recover before the next shift.

A US survey of coal mine workers found that by age 50, around 90% of workers had some hearing loss compared to just 10% of males of the same age not exposed to occupational noise. NIHL gradually worsens with continuing exposure to noise and most workers are unaware of their hearing loss until it becomes obvious to other people, and by then the hearing loss is severe.

Sometimes hearing loss is detected only because the worker complains of a loud ringing or hissing noise in their ears. This condition, known as tinnitus, is often associated with NIHL. Sufferers sometimes find the constant noise almost unbearable, particularly when background sounds are low at night.

The only good thing about NIHL is that it is entirely preventable.

Preventing noise induced hearing loss - employers

Employers in noisy industries should develop effective hearing conservation programs for their workers which involve:

Noise level monitoring

• Monitor workplace personal noise dose (adjust exposure standard for 12 hour shifts)
• Develop workplace noise maps by area monitoring
• Install appropriate signage in noisy areas
• Convey results to workers.

Training and education

• Develop a noise training and awareness program
• Involve management and supervisors
• Undertake personal counselling for workers with difficulties (e.g. compliance or personal health issues such as ear canal infection)
• Evaluate the program.

Controlling noise

Apply appropriate noise control measures. (The standard hierarchy of controls applies):

• Elimination - Redesign work and workflow to eliminate noisy jobs
• Substitution - Replace noisy machines/processes with quieter alternatives
• Engineering
  • Separate noisy machines and people - enclose noisy machinery where possible or enclose personnel in noise reduction cabs or control booths
  • Dampen noise transmission and reflectance pathways e.g. stiffen vibrating structures, fit rubber mounting on machinery and apply sound absorbent materials on noise reflecting surfaces
• Administrative
  • Minimise exposure of personnel with job rotation, rostering etc
  • Provide low noise crib rooms
  • Shorten shift lengths (remember 12 hour shifts require appropriate adjustment (lowering) of the exposure standard)
  • Create a purchasing policy requirement for quieter equipment.
• Personal protective equipment
  • Offer choice of PPE (plugs, muffs)
  • Provide training on fitting, use and maintenance
  • Evaluate effectiveness and compliance
  • Provide a PPE maintenance program
  • Develop an enforcement policy
  • Ensure supervisors/managers set a good example, especially in noisy areas.

Audiometry

• Provide audiometry on entry to company
• Provide audiometry at regular intervals depending on exposure (measured by personal noise dose monitoring)
• Document follow-up actions and
• Keep good records

Program evaluation

Evaluate performance of the program and of key personnel on an annual basis.

Preventing noise induced hearing loss – workers

As a rough guide, if you must raise your voice to communicate with someone standing a metre away, the noise level is almost certainly too high and may be damaging your hearing. Hearing protection, which can be plugs or ear muffs, (both provide adequate protection for most noisy situations if correctly worn), should be used until other measures can be considered.

While hearing loss is permanent, it will not worsen over time if further exposure to excessive noise is avoided. Therefore it is important that everyone, even those with some hearing loss already, take all possible care to avoid excessive noise exposure.

Insertion and use of ear plugs

Ear plugs can't provide sufficient protection if only partially inserted, so it's important they're inserted correctly. This reduces the risk of ear canal infections. New plugs should be used after each crib or other rest break:

1. To prevent ear infection, ensure that hands are clean to avoid introducing dirt and grease into the ear canal.
2. Roll the plug into a thinner cylinder and with the opposite arm over the top of the head, pull the ear backwards to straighten the ear canal.
3. Insert the rolled plug well into the ear canal and hold in place for 30 seconds. The plug will expand to its former size, forming an effective seal. Repeat with the opposite side. Only the tip of the plug should be visible.
4. Remove ear plugs during rest breaks in quiet areas so the ear canal can lose accumulated moisture.

Other hearing protection

Ear muffs are as effective as ear plugs and the choice should be left to the individual worker. Ear muffs should be comfortable, not too tight, and must provide sufficient noise reduction to below the safe exposure level. Avoid excessive hearing protection as it may cause communication issues.

Ear muffs should form an effective seal around the ear. Thick hair or the temple pieces (arms) of glasses can prevent a proper seal.

When not in use, store earmuffs somewhere clean and dust free to help prevent ear infection.

Like ear plugs, ear muffs should be removed during breaks in quiet areas to allow the ear canal to lose accumulated moisture. Ear drops used to prevent "swimmers' ear" infection may help prevent recurrent ear canal infections in hot conditions.

How does the ear detect sound?

Sound is caused by air pressure waves from a vibrating object funnelling into the ear drum which vibrates at the same frequency.

Three tiny bones attached to the inside of the ear drum, called the hammer, anvil and stirrup, carry the vibrations across the air–filled space known as the middle ear, to the inner ear and the organ of hearing, the cochlea.

The cochlea is a spiral shaped hollow, filled with fluid. It contains many specialised hair cells that detect vibrations arriving from the ear drum. The hair cells convert the fluid vibration into nerve impulses which pass to the brain, which detects them as sound.

How does noise damage hearing?

NIHL occurs when sensitive hair cells of the cochlea are damaged by loud noise. Hearing will recover at first, but with regular loud noise exposure, the hair cells may die, resulting in serious and irreversible deafness.

Noise levels are measured in decibels (dB). Levels averaging above 85dB for an 8 hour shift, or 82dB for a 12 hour shift, can cause hearing loss. Damaging noise energy doubles for every 3 decibel rise, e.g. 86dB represents twice the sound energy of 83dB.

How much noise is damaging?

The amount of noise energy entering a person's ear over a work shift determines how much hearing damage results. Very high noise energy (loud noise) can deliver as much noise energy over a few minutes as a much quieter sound over several hours.

Therefore, the louder the average noise experienced by the worker, the shorter the maximum permitted exposure time should be before there is a risk of hearing damage. As shown on the graph below, by the time the average noise level reaches 100dB (A), the maximum permissible exposure is only 15 minutes.

How does the hearing test work?

A hearing test is part of every coal mine worker's full medical assessment. It detects how sensitive the person's ears are to sounds at different frequencies. For a worker with hearing loss already, the sound must be louder before it is heard, so the increase in loudness required reflects the amount of hearing loss. The result is recorded on a graph called an audiogram.

What does the hearing test show for a person with NIHL?

For NIHL, the main hearing loss occurs at around 4000 hertz frequency at first (3-9 years), which shows as a V shaped 'notch' in the audiogram. With further noise exposure, the loss worsens and frequencies above and below 4000 hertz can also be affected. Ultimately, if there is inadequate protection against further noise, the hearing loss can involve the speech frequencies below 3000 hertz, making conversation difficult to understand and impacting seriously on the person's ability to communicate.

Authorised by Stewart Bell - Deputy Director-General and Commissioner for Mine Safety and Health, DNRM

Contact: minesafetyandhealth@dnrm.qld.gov.au

Issued by Queensland Department of Natural Resources and Mines