By Zalewski, Edwin
Occupational Hazards , Vol. 68, No. 9
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. …