Published in September 2009 Australian Longwall Magazine

The most recent data from the Australian Safety and Compensation Council, from 2006-07, shows coal mining as the worst mining sector for this health issue.

The national compensation data had the coal sector accounting for 17% of claims for long-term exposure to noise, compared with 9% for the whole mining industry.

Coal also accounted for 17% of claims for deafness.

Coal Services Health manager Mark O’Neill said analysis of the Coal Mines Insurance scheme indicated the number of claims for hearing loss was on the increase in New South Wales.

“In the 2008-09 accident year approximately 42 per cent of all hearing loss claims were for workers in longwall mines. This is up from 38 per cent the previous year,” he said.

Outside of the scheme, O’Neill said 33% of all claims for hearing loss in the state came from the underground mining sector while 25% came from surface mining.

CS Health assessed 7768 coal miners in the state during the 2008-09 financial year.

The data revealed 89% of the workforce had 0-5.99% hearing loss in one or both ears, while 8% had 6-15.34% hearing loss and 3% exceeded 15.34% hearing loss.

“When comparing this to the age demographic for workers, we find that 9 per cent of workers at the age of 35 can have a level of hearing loss greater than 6 per cent,” O’Neill said.

“This moves to 16 per cent at age 45, and 44 per cent at age 55.”

In comparison to the general population, O’Neill said in 2005 there was an estimated 3.55 million Australians with hearing loss in at least one ear, with 64% aged over 60 and 37% aged over 70.

Sifting through the recent data, O’Neill isolated the youngest claimant for occupational hearing loss, a 35-year-old employee of a contractor and labour hire company.

The level for compensable hearing loss is 6% and above, while this employee had confirmed hearing loss of 10.2% after seven years in the mining industry.

“Occupational hearing loss is irreversible and impacts drastically on the quality of life one may expect to enjoy,” O’Neill said.

While NSW is trending for the worse for noise-induced hearing loss claims, the most recent data for Queensland reveals there were 24 NIHL workers compensation claims in the 2007-08 financial year, almost half the 46 claims in the previous year.

In longwall mining, the main sources of noise come from shearer operation, coal transport along the AFC, the BSL-mounted crusher and coal transport in the maingate along with pneumatic tools used for maintenance.

The whole process of longwall mining is inherently noisy and with steel on steel machinery involved, OEMs are yet to engineer out this hazard.

Peter Tiernan, manager of the Queensland government’s Health Surveillance Unit, which operates under the Department of Employment, Economic Development and Innovation, is well aware of the health issue.

“The problem with noise-induced hearing loss is that it is so insidious – you have no idea it is happening until it is too late,” he said.

Hearing damage can occur when noise exceeds 85-90 decibels “A” scale.

While average noise levels of 92-100dBA and peak levels of 133-143dB “C” scale were typically encountered on the longwall face, Tiernan said good-quality ear plugs fitted correctly and worn continuously provided adequate protection.

He said a decrease of 3dBA in the level of noise reaching the ear represented a 50% reduction in acoustic energy, lessening damage to the worker’s hearing.

Off-the-shelf ear plugs are used at most sites rather than moulded ones, but Tiernan warned that headband earplugs, used to avoid dirt contamination from the fingers, usually did not provide the same level of hearing protection.

“To counter this issue, plugs are available that are inserted by holding a shaft instead of rolling the ear plug and which will provide adequate attenuation,” Tiernan said.

“Contamination from fingers is always an issue with ear plugs although it is not a medical problem as the dirt does not go past the eardrum where it can cause infection.”

As the longwall sector relied on personal protective equipment to combat hearing loss, Tiernan noted it was often left up to individuals to make sure they always wore protection.

The protection provided by ear plugs or ear muffs varies widely depending on how well they fit and the length of time they are worn.

CS Health statistics support the widespread use of PPE with 88% of the 7768 miners assessed in 2007-08 using full hearing protection and less than 1% with “poor” hearing protection use.

Of those miners only occasionally wearing hearing protection, O’Neill said most were in the 50-54 age group.

But Tiernan said PPE did not remove the hazard and was regarded as a soft barrier.

“A major challenge exists to identify more robust higher-level control measures.

“Noise limitations are being written into specifications for longwall purchases and equipment suppliers are addressing how to comply with the new limitations.”

He said more work needed to be done with original equipment manufacturers to design and implement engineering solutions to reduce noise, or isolate the process as in automation.

The US National Institute of Occupational Safety and Health has been studying the use of acoustic insulation to cover the undersides of the shields, shearer body and shield supports.

The research indicates a 2-3dB reduction between the shearer drums and a 4-5.5dB attenuation upwind of the headgate drum can be achieved.

Tiernan said this attenuation reduced noise to between one-quarter and half of the original level.

Automation is the other key area of research into minimising hearing loss in longwall mining, with shearer operation taking place remotely and safely away from the face, but the technology still needs more development.

To help reduce hearing damage the Health Surveillance Unit has a number of recommendations for longwall operations.

A baseline noise exposure should be established for each site by measuring levels, with further noise surveys to be undertaken when sound levels from equipment increase or process changes and at least every five years.

HSU recommends specific action to be taken when workers are exposed to an average noise level of more than 85dBA for an eight-hour shift or a peak noise level exceeding 140dBC.

“When shifts longer than eight hours are worked, the exposure levels measured must be adjusted for comparison with the eight-hour limit,” Tiernan said.

“A company may adopt internal management action levels below these limits and the Health Surveillance Unit would encourage such an approach.”

HSU also recommends sites use the Cirrus CR:110ASIS doseBadge personal noise meter to measure noise levels, as it has been certified intrinsically safe for use underground.

“These devices also measure peak exposures accurately, which was always a problem with past noise meters,” Tiernan said.

Overall, Tiernan said there should be an emphasis on engineering controls to reduce noise, followed by a decrease in exposure time.

Looking at NSW longwall mines, O’Neill said some operators were monitoring noise on an infrequent basis.

“Some are conducting noise monitoring on an ongoing basis utilising a similar exposure group-based system,” he said.

“The majority, though, continue to take a watchful, waiting attitude while not implementing any specific monitoring programs.”

While wanting to see a greater focus on education, awareness and control measures, O’Neill said there was also scope for large mining companies to work together with OEMs to improve research and development on noise mitigation for mining equipment.

As well as NIHL, excess noise can lead to distractions, an inability to hear warnings or alarms, and noise-induced fatigue.

The Queensland Mining Health Improvement Awareness Committee, comprising government safety officials, mining unions and industry organisations, discussed NIHL prevention at its September quarterly meeting.

The Queensland Mines Inspectorate and the state’s mining industry also addressed the issue at their September 17 seminar on strategies to reduce NIHL risks and will share the outcome.

With some research indicating that workers are more likely to use hearing protection because of exposure to loud noise, rather than awareness programs, Tiernan said it seemed the message might not be getting through.

Two websites offer hearing loss self-tests are www.cdc.gov/niosh/blog/nsb051208_quickfit.html and www.cdc.gov/niosh/mining/products/product47.htm