Stop that noise!
The annoyance of noise has no doubt plagued man since the beginning of time. Can you imagine a caveman grunting at a something-or-other-saurus for disturbing his sleep? JACO DE KLERK discovers annoyance is the least of man’s noisy problems
It’s Sunday morning and you get to sleep in. Blissful. You may slip in and out of consciousness, images of kittens, unicorns, rainbows and fairies filling your early morning dreams. If life was a musical, this is where you’d break into song: … The hills are alive with the sound of … – weed-eaters? Seriously? You’re catapulted back to reality. You leap out of bed, knock over a lamp and trip over the dog before realisssssing that your neighbour is tending his garden.
Noise. Can’t live with it, can’t live without it; rules and regulations have been the order of the day for centuries.
In ancient Rome, the noise made by iron-wheeled wagons as they pummelled the cobblestones was regulated to ensure that sleeping Romans were not disturbed. Several Medieval European cities, meanwhile, prohibited night-time carriages and horseback riding to make sure residents got a peaceful night’s sleep. Such noise problems seem insignificant compared to those of modern society – trucks, aircraft, trains, power tools, heavy machinery, weed-eaters and hair dryers – that interrupt our leisure time and relaxation. But that’s the least of our problems. It’s been proved that ongoing high noise levels could damage the hearing of an entire workforce.
Dangers of noise
Noise-induced hearing loss (NIHL) is the impairment of someone’s hearing, usually resulting from exposure to excessive occupational noise and generally over an extended period of time – some months or years. Such hazardous noises can damage hair cells situated in the inner ear that convert sound energy into electrical signals that travel to the brain. Once damaged, these small sensory cells can’t grow back. NIHL can also be caused by acoustic trauma – for example, a single exposure to an intense sound, such as an explosion.
Sound is measured in decibels (dB), with an increase of 10 on the decibel scale meaning a sound is 10 times more powerful and sounds twice as loud to your ears. That puts things into perspective if you consider the humming of a refrigerator is 45 dB, normal conversation approximately 60 dB and dense city traffic up to 85 dB – which could cause hearing loss with continuous exposure. As a rule of thumb, if you experience any difficulty hearing a normal conversation two metres away from the speaker, the surrounding noise levels are probably above 80 dB.
Noise doesn’t only have a physiological effect on a workforce but can also have a psychological one, such as stress, reduced processing capacity and post-work irritability – which makes it extremely difficult for employees to relax and unwind. That will, in turn, affect the duration a worker spends on a specific task; by placing greater demands on a worker’s attention, which can affect concentration, noise can effectively increase the cost of doing a job. High noise levels can also interfere with communication in the workplace, leading to an increased risk of accidents, since it will be more difficult to hear approaching dangers and warnings.
Protecting the workforce
Impala Platinum developed a hearing conservation programme to protect its employees and contractors against this danger. The programme ensures noise is reduced – anywhere underground or on the surface – where levels exceed 85 dB and has been created in accordance with the Mine Health and Safety Act, 29 of 1996, and the Minerals Act (Act 50 of 1991, Chapter 34). These Acts makes mines’ conservation programmes legally binding, and a punishable offence if not complied with, guaranteeing the protection of the workforce against hazardous instructions – such as being told that to work while there’s excessive noise nearby. Impala acknowledges that its hearing conservation programme is only an outline of the minimum requirements for the safety of its workers, and implements further safety measures as needed.
The mine has also employed mandatory routine audiometric examinations (tests that measure the sharpness and acuity of an employee’s hearing over time) for all employees who are – or may be – exposed to dangerous levels of noise. These tests are carried out on all pre-employed staff to establish a baseline level, and again when an employee leaves. The tests are also conducted on workers who have experienced an acoustic trauma. To facilitate this process – protecting the workforce and the mine – Impala requires each employee to furnish an exit medical examination certificate before they receive their final payment.
Impala manages excessive sound by buying less noisy equipment, or muffling and silencing machinery that doesn’t have a quieter alternative. Instances where such measures are employed include:
• Boiler exhausts, where high pressure steam is vented through a large pipe several times a day, producing low-frequency noise at high levels. This problem was dealt with by fitting a perforated cone diffuser to existing ventilation pipes – splitting the single exhausts jets into many smaller ones, which lowers the velocity and reduces the noise. This apparatus also transforms the noise frequency from low to high – making it easier to muffle. An absorbent attenuator is added to further reduce the noise emissions – achieving an overall noise reduction of up to 40 dB without any loss of performance.
• Compressed air cleaning guns generate violent air turbulence and produce unacceptable noise levels at the outlet. Impala addressed this problem by replacing the single-jet nozzles with compound ones, producing a ring-shaped air stream at lower speeds around the main high-speed one. This smoothes the transition of the high-speed stream into the surrounding still air, reducing the noise by 20 dB.
• High-velocity exhaust air emitted from the handle of a hand-held pneumatic grinder causes turbulence and noise in the surrounding air. The mine solved the problem by stuffing the handle with steel wool to distribute the exhaust air and reduce the velocity, resulting in a noise reduction between of 15 and 20 dB.
• Sharp bends, closely spaced control valves and internal build up of scale (a hard greyish-white substance sometimes found inside water pipes and water heating containers) creates turbulence in pipes and ducts, which hinders the flow of the material being conveyed and generates noise. Impala installed smoother bends to reduce turbulence and increased the distance between control valves to stabilise the material before it reached the next valve, decreasing noise levels and improving the performance of pumps.
To further reduce incidents of NIHL, Impala implemented a noise-related training programme for all its employees. When new staff, contractors or personnel returning from leave arrive on the mine, they have to report to the training centre for training or refresher courses, which cover all relevant aspects of hearing conservation. Impala is also taking measures to prevent employees who have NIHL from being further exposed to damaging noise levels by transferring them to other tasks or to areas where there’s less noise.
Harmony, AngloGold-Ashanti and the Aquarius Group have implemented noise management strategies similar to Impala’s. The aim is to limit dangerous noise levels by installing machinery that emits lower levels of noise or by using silencing equipment if quieter machinery isn’t available. Those mines are furthermore complying with the requirements of the Mine Health and Safety Council through their commitment to industry targets – ensuring employees’ hearing ability doesn’t deteriorate by more than 10 percent due to occupational NIHL – and by installing equipment that doesn’t exceed sound levels of 110 dB in the workplace. Harmony, Ashanti and Aquarius are also conducting audiograms of all occupationally noise-exposed employees when they join the company and annually thereafter.
The mines use hearing protection products to further guard their workforce. Companies may use basic earplugs in areas where noise levels aren’t too excessive for employees’ safety. Low foam earplugs can be used if staff have to wear such equipment for long periods, as they place less pressure on the ear canal. When noise levels climb above the 85 dB mark, mines rely on earmuffs for noise protection. Earmuffs can drown out loud noises, but should be cautiously selected, as over-protection can occur. Where too much sound is blocked out, workers won’t be attuned to their environment and possible approaching dangers. Mines can deal with that by purchasing earmuffs that block out loud noises – above 85 dB – but allow softer sound – below 75 dB – to be heard, thus enabling employees to hear warnings and speak to one another.
Keeping more than just the ears covered
NIHL is one of the most common health risks the mining industry is beset with and is covered by Rand Mutual Assurance (RMA), as it’s a scheduled compensable disease in terms of Schedule 3 of the Compensation of Occupational Injuries and Diseases Act. This form of hearing loss is responsible for roughly 15 percent of all the claims submitted to RMA and accounts for approximately 45 percent of the costs paid out by the company to claimants.
RMA also covers deafness due to trauma – for example, a head injury – and acoustic trauma. However, an employee’s right to benefits lapse if not brought to the attention of the employer, Compensation Commissioner or the RMA within 12 months of onset of the problem. The date the ailment starts is the date of the first audiogram that shows a hearing loss of 10 percent or more than the initial audiogram the employee took. HIV, Aids and Highly Active Anti-retroviral Therapy may also cause hearing damage, which can’t easily be distinguished from NIHL. This and other non-work related hearing loss, such as ageing, may hamper employees’ compensation – and the fight against NIHL itself.
So the next Sunday morning when you have the blissful chance to sleep in and your mind fills with everything sparkly and wonderful and the hills start to roar with the sound of weed-eaters… put in some earplugs or have a long talk with your neighbour. Annoyance is perhaps the mildest of mankind’s noise-related problems.