An OSHA inspection at an Atlanta steel mill resulted in a citation for failure to reduce sound levels that could damage employees' hearing. The noise exposures for an 8-hour day were between 91 and 94 decibels (dB).
An expert witness testified that a three-sided booth built around the noisy equipment would reduce the noise level by 7 to 10 dB, and a fourth side would provide another 5 to 7 dB reduction. Other proposals to reduce noise included replacing cooling fans with larger, slower fans and enclosing the employees' break area to block noise from workers on break.
Actions that reduce the amount of noise, like replacing a fan and building enclosures around equipment, are called engineering controls. Replacing the fan would be a "source control" because it removes a source of noise, and the enclosure would be a "path control" because it blocks the sound from reaching employees' ears. Administrative controls also can reduce noise exposure by moving employees to quieter areas, or operating noisy equipment on different shifts.
Although OSHA requires employers to evaluate engineering and administrative controls before using personal protective equipment, most people first think of earplugs when they need to protect workers' hearing in a noisy workplace.
Source and path controls are an essential part of an effective hearing loss prevention program. Reducing noise levels can save money because fewer employees require annual hearing tests. Controlling noise even can reduce worker stress and improve morale. Of course, reduced noise levels also help protect employees' hearing.
The hazard from noise depends on the volume (intensity) and duration of exposure. The louder the noise and the longer the exposure, the greater the potential for hearing loss. The risk also builds over a single workday.
Engineering and administrative controls can be thought of as "removing the hazard" and "removing the worker." Source and path controls are the most effective because they reduce the amount of noise produced or the intensity of noise that reaches employees. After examining these control options, move on to administrative controls, and consider hearing protection as the final line of defense.
To get started, you first need to identify the sources of noise and evaluate your workers' exposure.
Evaluate Noise Exposure
A plant-wide survey can identify operations or areas where noise levels are hazardous. Problem areas include places where talking in a normal voice is difficult, or where workers have ringing in their ears after working several hours in that area.
To thoroughly define the noise problem, you need to:
- Measure noise levels;
- Develop information on employee exposure; and
- Evaluate the need for noise reduction.
Identify individual noise sources, examine how sound is transmitted to the room or amplified through vibration and determine how much these sources contribute to the overall noise levels. Noise sources can include motors, gears, belts and pulleys, points of operation where blades touch wood and other moving parts. Transmitters include equipment frames, footings and housings.
Finally, evaluate potential controls. The methods chosen will depend on the amount of noise reduction needed, as well as the costs of purchasing, operating and maintaining the system.
Reduce Noise at the Source
Source controls include equipment modifications to reduce the noise generated. In some cases, a relatively simple solution reduces noise enough that hearing tests and hearing protection are no longer needed. In other cases, the solution requires several stages of installation over a period of time.
Each reduction of a few decibels reduces the hazard and reduces noise-related annoyance, which can boost productivity as the workplace becomes more comfortable. Examples of source controls include:
- Placing noisy machinery in a separate area away from as many workers as possible;
- Maintaining equipment in top operating condition through lubrication and cleaning, replacing worn parts, maintaining proper belt tensions and properly balancing pulleys, blades and other rotating parts;
- Reducing the speed of operation to the slowest level consistent with product quantity and quality goals;
- Moving power equipment out of wooden or steel-frame buildings and into stone, cement or brick structures;
- Reducing vibration by ensuring equipment frames are rigid and equipment is firmly seated on a solid floor (preferably cement) and is not in contact with other equipment or with walls;
- Isolating noisy equipment using rubber footings, springs or other forms of damping to reduce vibration that could radiate or amplify the noise; and
- Applying damping materials to vibrating surfaces and constructing sound-absorbent hoods around points of operation.
You may want to consult an acoustical specialist to help evaluate and install vibration isolators and damping material. Properly applying damping material is a complicated process that considers the sound frequency, the noise reduction desired and the weight and size of the machine. Generally, the damping layer should be the same thickness as the surface being treated.
Another solution is to begin a "buy quiet" program and specify low noise levels when purchasing new equipment. Many types of noisy equipment are available in noise-controlled versions, and a "buy quiet" policy can reduce noise levels as older equipment gets replaced with newer, quieter models.
Stop Noise from Reaching Workers
Path controls involve isolating, blocking, diverting, absorbing or otherwise reducing noise intensity before it reaches employees' ears. Some equipment, like saws and punch presses, can't be made to run any quieter. Noise exposure to non-operators can be reduced by absorbing the noise or installing barriers to block the noise. Examples of path controls include:
- Using sound-absorbing acoustical tiles and blankets on floors, walls and ceilings;
- Enclosing equipment within barriers designed to absorb noise or reflect it in harmless directions, such as toward ceilings covered with sound-absorbent material; and
- Moving noise-producing equipment away from employees, since noise intensity decreases with distance. Surfaces such as metal walls that reflect sound back toward employees will limit the noise reduction achieved by this method.
Other factors need to be considered when path controls such as enclosures or reflecting walls are used. For example, lighting and ventilation need to ensure comfort, and reflecting walls should not interfere with fire sprinklers. Also, path controls should not interfere with equipment operation or maintenance.
Employees who work with the equipment can provide guidance on matters such as the position of controls, lubrication and servicing points and the location of access doors for maintenance.
Remove the Worker
Administrative controls involve changing work schedules or operations to reduce exposure. Examples include operating noisy machines on the second or third shift when fewer people are exposed, or shifting an employee to a less-noisy job partway through a work shift. These controls are often not practical for reducing noise exposure for two reasons:
1. You may not have enough employees trained in a particular task to allow for job rotation.
2. Rotating employees between quiet and noisy jobs may reduce the risk of severe hearing loss in a few workers, but increase the risk of small hearing loss for many workers.
If you consider arranging work schedules to reduce noise exposure, keep these concerns in mind and evaluate the potential impact on all affected workers.
One practical solution that removes the worker from the hazard is to provide quiet areas for relief from noise. Designate break and lunch areas away from noise or isolate them with sound barriers. This will reduce total noise exposure over the working day.
Hearing protection becomes necessary when other controls cannot reduce noise to a safe level. Hearing protection is effective and, compared to other controls, relatively inexpensive.
Although wearing earplugs can protect hearing, the protection does nothing to reduce stress or discomfort from excessive noise exposure. Also, a hearing protection program requires ongoing effort and commitment. Specifically designed protection is required, depending on the type of noise and the employee's condition.
Using more than one protective device seems a logical response for high noise exposure. Some employers assume that wearing an earmuff with a noise reduction rating (NRR) of 28 dB combined with an earplug having an NRR of 24 dB would provide a total reduction of 52 dB. Unfortunately, this is not accurate. High noise levels bypass the outer and middle ear and stimulate the inner ear through a process called "bone conduction." Therefore, dual protection only adds an additional 5 to 10 dB of noise reduction.
Benefits of Noise Reduction
A hearing loss prevention program is good business, and it protects employees' hearing and ability to communicate. With no cure for noise-induced hearing loss, preventing exposure is the only way to avoid hearing damage. Because hearing loss creeps up slowly, many individuals are not aware of the damage until it is too late. Long-term noise exposure also may contribute to stress-related disease, especially cardiovascular disease.
Noise also can affect productivity. Studies show that employees in effective hearing loss prevention programs generally feel less tired and irritable. They report that they sleep better, and do not experience temporary hearing reductions at the end of the day or ringing in the ears that often precedes hearing loss. Companies with effective hearing loss prevention programs also showed reduced accident rates, illnesses and lost time.
In short, a good hearing loss prevention program is good for worker health and good for business. The company benefits from reduced workers' compensation payments and medical expenses, and a reduced likelihood of an OSHA citation.
Hearing loss prevention programs should extend beyond the workplace. Encourage employees to take earplugs home to wear during woodworking, target practice or other noisy activities to reduce the chances of questionable work-related claims. Employees who work for 35 or 40 years deserve to enjoy retirement. They should be able to socialize with family and friends, and listen to music and the sounds of nature.
Edwin Zalewski is an associate editor with J. J. Keller & Associates Inc. He has more than 10 years of experience working on environmental and safety compliance issues.