Sound Off

Preventing Hearing Loss in the Mining Industry

Of our five traditional senses, one that many of us take for granted is our ability to hear. We recognise the importance of wearing protective lenses to shield our eyes when using power tools, or putting on a mask while working around mould and dust, yet hearing protection, it seems, often takes a backseat to our other senses.

In extremely loud areas, such as airports, factories and mine sites, a lapse in the proper use of ear protection can have potentially devastating results, from a temporary ringing in the ears to permanent hearing loss.

Worldwide, men and women working in the mining industry remain especially vulnerable to noise-induced hearing loss, and sites in Australia are no exception. Over the decades, countless miners have lost their hearing, some of them temporarily, many permanently. In the United States, it is believed that over 75 per cent of coal miners have impaired hearing from exposure to noise by age 60, and it is estimated that 90 per cent of coal miners will have hearing loss by the time they retire.

Hearing loss does not discriminate between young and old, male and female. While some people with minor hearing loss can still benefit from mechanical amplification, others are considered profoundly deaf and beyond mechanical help. There are four types of hearing loss: conductive, mixed, central, and the last, sensorineural, which comes from damage to the tiny sensory hair cells and/or the nerves in the inner ear. Although there is promising research in mice around the sensory hair cells of inner ear these hairs, once damaged by drugs or frequent exposure to noise levels exceeding 85 dB, do not repair themselves in humans as they do in amphibians and birds. The damage ranges from mild hearing loss to deafness so severe that not even a hearing aid will work.

The Challenges of Hearing Loss

In the mining industry, hearing loss due to excessive noise is a challenge. It is estimated that one out of every four mine workers worldwide has a serious hearing problem, with miners being exposed to the greatest amount of hazardous noise of all major industries, according to the Office of Mine Safety and Health Research (OMSHR) in the United States. The culprit: noise-induced hearing loss, or NIHL, which affects miners working both above and below ground. Those with NIHL can be affected in a number of ways, from experiencing annoying buzzing or ringing sounds known as tinnitus to permanent hearing loss.

NIHL affects mine workers worldwide. According to Hearing Loss in Australia – a report from Australian Hearing – “The most significant cause of hearing loss in Australia is exposure to loud noise. 37 per cent of heading loss is due to excessive noise exposure.” The personal cost of hearing loss, which can result in depression from being unable to communicate with friends and family, feelings of isolation, stress, accidents, reduced productivity and fatigue, also has dire economic consequences. In mining, hearing loss presents a number of risks, from being unable to communicate with other workers to the inability to hear machines or alarms. Most of us hear sounds in the 20 to 20,000 Hertz (Hz) range; individuals suffering from NIHL will initially have difficulty hearing in the 4,000 to 6,000 Hz range, where higher-pitched sounds, such as the voices of children, are hard to hear and understand.

Reducing the Noise

Worldwide, occupational hearing loss remains one of the most common work-related illnesses, costing those who suffer from it anguish, and the industry hundreds of millions of dollars in compensation claims. Miners in particular are not only exposed to noise 85 dB and greater from pneumatic percussion drills, screens, crushers, ventilation fans and blowers, cutting heads, conveyor systems, shovels, engines, blasting and other sources, but are often exposed to the sounds for longer periods of time than workers in other industries. In some cases, the peak exposure is 140 dB in mines. In mines, there is also the issue of background noise or “masking” which interferes with a worker and his or her ability to process one sound due to the presence of a second sound. The greater the degree of background noise the harder it is to comprehend speech, which can lead to dangerous situations in mines where one worker cannot understand warnings from another.

Fortunately, quieter gear drives, better mechanical designs which reduce impact points, remote controlled percussion drills, and other technologies are evolving to help reduce noise at mine sites. The most immediate, and in many ways the least expensive solution, is to control noise at the source. This includes regularly scheduled maintenance and lubrication of equipment and replacement of worn parts, repairing or replacing mufflers, maintaining fan silencers, custom-moulded earplugs, and the proper use of hearing protective devices, or HPDs. To be effective, HPDs must not only be a proper fit for the wearer, but must offer sufficient hearing protection for the mining environment in which they are used. In Australia, manufacturers have created relocatable soundproof panels which can be used to cordon off loud areas to protect workers, along with acoustic enclosures which can be used in the mining and manufacturing industries.

Worldwide, there have been a number of other innovations developed to reduce the amount of noise that reaches the ears of miners. These include a dual-sprocket continuous mining machine which reduces sound levels by two to three dB at the ear of the operator; a drill bit isolator which reduces noise by two to five dB; and a dual-sprocket urethane-coated continuous mining machine chain, which reduces noise at the ear of the operator by five to seven dB. Despite these and many other recent engineering advancements to suppress excessive noise, Australian miners still depend on HPDs to protect their hearing, which have a number of disadvantages. While conventional ear-covering HPDs help to guard against mine site noise, they also make it difficult for one worker to understand what another is saying, which can result in staff taking off their HPD to communicate, defeating the purpose of the hearing protectors.

Although the Mines Safety and Inspection Act (1994) outlines measures to ensure safe working environments, the best option remains avoiding excessive noise (administrative controls) whenever possible. Since this is not always possible when working with cutting and drilling tools or around loud dust suppression and ventilation equipment, HPDs such as muffs and/or plugs are necessary, but can be cumbersome. Fortunately, new electronic technology allows some “passively attenuated sounds” to pass through the HPD, and the selective restoration of some of these sounds comes through sound restoration hearing protection devices, or SRHPDs.

Excessive noise affects all miners, from those working on the surface to workers toiling deep underground. Along with technological improvements, there are other ways the mining industry can address NIHL, such as efficient noise controls for mining equipment in the short and long-term, and implementing these controls across the entire industry. From acoustic screens to improved HPDs, controls to reduce noise from roof bolting machines, and rigorous ongoing maintenance of existing machinery and equipment, it is possible to reduce excessive noise to improve safety, efficiency, and productivity on all mine sites. Targeting excessive noise at the source by implementing engineering controls such as collapsible drill enclosures, urethane coatings on flight bar chains and dual-sprocket chains help reduce noise for machinery operators and those working around them.

According to Australia’s Workplace Health and Safety Regulation (2008), ‘excessive noise’ is considered to be a) an eight hour equivalent continuous sound pressure of 85 dB or b) a peak sound pressure level of 140 dB. Over time, exposure to excessive noise can result in irreversible hearing loss. Fortunately, NIHL can often be prevented through analysis of noise in a work environment and preventative steps taken to reduce exposure to excessive noise. Evaluation of the cause of the noise is critical, as it will help to evaluate the extent of the problem and determine the best approach to take. Tables exist which detail the maximum allowable duration in hours and the sound level in dB. Barriers which are impervious to sound can be used to decrease excessive noise. Still, the best solution of all remains to decrease the volume of excessive noise at the source.

In the future, as quieter machines are engineered and better protection evolves to filter out harmful noises but still allow Australia’s mine workers to communicate with one another, it is hoped that hearing loss will become a thing of the past.

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July 26, 2017, 12:29 PM AEST