Hearing Loss Prevention (Noise)

Chapter 296-817, WAC

Effective Date: 08/01/03

Helpful Tools

Chapter 296-817 WAC

Helpful Tool: Eliminating Noise

How can noise be eliminated from the workplace?

When noise monitoring results indicate that workers are exposed to harmful noise levels, the best way to protect them is to eliminate the noise exposure versus using personal protective equipment. Using personal protective equipment can have many drawbacks and will not always be effective. Even small flaws in the fitting or use of hearing protection will significantly reduce its effectiveness. Sound can also be transmitted directly into the inner ear through the skull and have other effects on the body, so there are limits to the effectiveness of hearing protection. Small flaws in fitting or using an earplug or earmuff may not be apparent until a year or two after an employee starts using it, when follow-up testing is conducted. By that time irreparable hearing loss may have occurred.

Eliminating Noise at the Source

Quieting the noise source directly will often be the most efficient way to reduce exposures. Most industrial noise is not part of the work, it is due to machinery operation or materials being worked on or handled. Often small changes in equipment or processes can significantly reduce noise with little change in the efficiency or effectiveness of the work site. There are a variety of ways to reduce noises at the source:

  • Install mufflers on engines.

  • Use silencers wherever gases are being released, particularly on the exhausts from compressed air actuated equipment.

  • Be sure equipment is in good operating condition—no squeaking parts, no rattling parts, etc.

  • Be sure equipment is operating as designed—compressed air pressures are set at manufactures recommended levels, motion is within design limits and not hitting stops or other objects, impact pressure is set correctly.

  • Use the correct equipment for the work—inefficient equipment may generate more noise and will usually generate noise for a longer time.

  • Damp noise producing machine panels and materials. Some panels and materials will work like drums or bells to produce noise when they are shaken, vibrated or struck. Damping means to hold the materials tightly to prevent them from continuing to vibrate or adding materials that absorb the vibration energy.

  • Move workstations further from noise sources.

In most cases noise in the workplace is a sign of inefficiency—energy is being used to make noise rather than products to be sold. The amount of energy necessary to create a harmful exposure is not great, but may be a sign of other inefficiencies in the system. Working to eliminate noise will often have benefits in improved efficiency and more effective production. A program to regularly monitor noise levels in the workplace will not only prevent over- exposure of employees, but may have added benefits such as identifying maintenance or adjustment problems with equipment and improving plant efficiency.

Noise Enclosures and Barriers

Where noise cannot be eliminated at the source, the next form of noise control is to use engineering controls to intercept the sound as it travels from the noise source to the workers. The most effective way to do this is to create a closed box either around the equipment or the worker. Enclosing the sound source should also include adding acoustic insulation to absorb the sound being generated to make the enclosure as effective as possible. Special care must be taken to make sure materials can enter the enclosure and that cooling air and other equipment needs are accounted for without excessive openings into the enclosure. Using entry tunnels and baffles can allow full access to the machinery without compromising the effectiveness of the enclosure.

Barriers may be simple walls or curtains of acoustic materials. Barriers have limited effectiveness unless they are very near either the noise source or the employee to be protected. Otherwise the sound tends to simply travel around the barrier. Placing a barrier around a particularly noisy work area may limit the noise exposure of other workers, but will typically not reduce the exposure of workers performing the operation.

Acoustical panels or baffles
Acoustical panels or baffles are commonly installed near particularly noisy machinery, either on walls or ceilings. These can effectively cut down reflected noise, but do not address the direct noise exposure, which is usually much more significant. These panels and baffles are best suited as additions or treatments of enclosures or barriers.

Buy Quiet Programs

The engineering controls discussed above are often much more cost effective when they are planned and purchased with the equipment. Typically, the equipment will be fitted for the control system, or the controls will be installed during manufacture. This also eliminates the costs of studying and designing the noise controls. By considering noise during planning and purchasing of equipment, it is also possible to take advantage of plant layout and design to minimize noise problems. For example, if a particular machine will be the primary noise source in the plant, the production floor may be arranged to make it simpler to isolate that machine.

Administrative Controls

Another strategy to controlling noise exposures is to change work practices to minimize exposures. In some cases, simply scheduling work appropriately or moving workstations away from high noise areas can result in a significant reduction in noise exposure. Where specific tasks or machinery are the primary noise exposure for employees not working directly with those tasks, moving these employees to other locations may eliminate their noise exposure with little effect on the processes involved. Where employees must move from one location to another, paths should be provided that allow them to avoid high noise areas.

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