Occupational safety and health

Many miners are exposed to one of the most insidious work-related diseases in the industry - that of noise-induced hearing loss (NIHL).

"The worst thing is that they don't know it's happening until it's too late," says Tsedi Taela, head of the audiology department at AngloGold Health Service's West Vaal Occupational Health Centre. "That's because the tiny hair cells in the ear, which send signals to the brain alerting us to sounds, get worn out gradually by long periods of loud sounds, or short blasts of extremely loud sounds. The result is that the signals don't reach the brain and sounds become imperceptible. This all happens without the noise-exposed employee noticing. Unfortunately, the hair cells are not replaceable so any hearing damage is permanent."

AngloGold Ashanti's approach to the challenge of NIHL is to firstly address the problem at source by muffling rockdrills, fans and other noisy underground equipment, and secondly to ensure that appropriate hearing protection devices are worn by those employees who are still exposed to excessive noise levels. Audiologists monitoring hearing at AngloGold Ashanti's Vaal River operations have recently embarked on research which they hope will provide some solution to early intervention, which, coupled with individual responsibility, should lead to more successful hearing conservation programmes.

Instead of testing in an audio booth at the Occupational Health Centre where employees would only visit once or twice a year, they decided to test a sample group closer to the workplace, and set up the audio booth at the point where miners exit the mine after work.

"Before one suffers any permanent hearing loss, exposure to high levels of noise may result in a temporary threshold shift (TTS), which recovers over the next 16 hours," says audiologist Anita Edwards, explaining why hearing loss can remain undetected. "Changes in hearing are small but they all mount up," she continues. Eventually they result in a permanent threshold shift (PTS), that is, permanent hearing loss.

By moving closer to the workplace, Edwards and Taela were hoping to measure the TTS. Their initial research findings have, however, shown unexpected results and are directing the audiologists into other areas of research in an effort to obtain greater accuracy and a more sensitive means of early identification of NIHL.

They will now test a larger sample group who are exposed to noise levels exceeding 85 dBA and they will move the test booth even closer to the workplace to reduce the time lapse between noise exposure and testing.

Taela and Edwards are also looking at audio testing using distortion product otoacoustic emission (DPOAE), an objective test, which can tell whether the function of the outer hair cells is damaged. The audiologists are hopeful that this will provide them with the information they require to successfully intervene earlier and thus prevent cumulative hearing loss.

But Edwards says that much of the responsibility for hearing conservation also lies with the employer and employee. "It's a mindset change. Employees need to take cognisance of the importance of wearing HPDs and be aware of the risks, and employers have a responsibility to their employees' health by muffling noisy equipment and by providing effective ear protection along with education on hearing loss prevention."