Noise control strategies are the first line of defense against excessive noise exposure. The use of these controls should aim to reduce, eliminate, or replace the sources of excessive noise and to reduce exposure to noise hazards to the point the risk to hearing is eliminated or minimized.
With the reduction of even a few decibels, the hazard to hearing is reduced, communication is improved, and noise-related annoyance is reduced. There are several ways to control and reduce worker exposure to noise in the workplace.
OSHA's hierarchy of controls for noise can be summarized as:
This hierarchy highlights the principle that the best prevention strategy is to eliminate the source of hazardous noise levels, and if that is not successful, manage exposure to those hazards through scheduling and the use of PPE. When it is not possible to eliminate the noise hazard or relocate the worker to a safe area, the worker must be protected with personal protective equipment.
The use of these controls should reduce hazardous exposure to the point where the risk to hearing is eliminated or at least more manageable.
For hearing loss prevention purposes, "engineering controls" is defined as any modification or replacement of equipment, or related physical change at the noise source or along the transmission path (with the exception of hearing protectors), that reduces the noise level at the employee's ear.
Typical engineering controls involve:
Simple engineering noise control solutions can reduce the noise hazard to the extent that audiometric testing, a hearing conservation program, and the use of hearing protectors are not necessary. Examples of inexpensive, effective engineering controls that can be applied include:
The diagram to the right shows how installing softer bends in the pipe and increasing the distance between the valves will reduce the turbulence in the line and, consequently, reduce the noise generated. Often, large pressure drops across valves, which cause noise, can be prevented with in-line diffuser silencers, which reduce the pressure upstream of the valve. Installing a muffler on the end of the nozzle is another option. All these methods can help reduce noise from compressed air sources.
Common examples of the implementation of such controls are:
Administrative controls, defined as "management involvement, training of workers, and changes in the work schedule or operations that reduce noise exposure," may also effectively reduce noise exposure for workers. Examples include:
Controlling noise exposure through distance is often an effective, yet simple and inexpensive administrative control. This control may be applicable when workers are present but are not actually working with a noise source or equipment. In open space, for every doubling of the distance between the source of noise and the worker, the sound level of the noise is decreased by 6.02 decibels. No matter what the scale of measurement, you will get a 6.02 decibels sound level drop for every doubling of distance.
Hearing protection devices (HPDs) are considered the last option to control exposures to noise. HPDs are generally used in conjunction with other hazard controls.
It is essential to the success of the program to have someone responsible for the selection of hearing protection devices and the supervision of their use. They must be able to evaluate and select appropriate devices for each employee, based on proper fit, the employee's noise exposure, hearing ability, communication needs, personal preferences, and other constraints imposed by job tasks or work environment.
Earplugs, earmuffs, or hearing bands alone might not provide sufficient protection from significantly high noise levels. In this case, workers should wear double hearing protection-earmuffs with earplugs. Avoid corded earplugs, as the cord would interfere with the muff seal. Additionally, hearing bands cannot be worn with earplugs or earmuffs, as the connected band would interfere with the muff seal, and there is no room to insert earplugs at the same time.
When fitting hearing protectors, attention needs to be given to each ear. It is not uncommon for a person to have right and left ear canals that are different sizes and must, therefore, be fitted with earplugs that are separately sized for each ear.
Ear canals should be inspected to assure that no physical problems, such as infections or excessive ear wax, will compromise or complicate the use of hearing protectors. Other employer requirements for providing hearing protection include:
Program implementers should be alert for common pitfalls associated with use and care of hearing protectors. For example, motorcycle helmets, personal stereo headsets, swimmer's earplugs, and hearing aids cannot be substituted for hearing protectors. Program implementers should be proactive in working with employees to avoid such pitfalls.
Attenuation refers to the damping or decrease of noise levels as a result of wearing HPDs. All hearing protectors are provided with an Noise Reduction Rating (NRR). Although earplugs can offer protection against the harmful effects of impulse noise, and some earplugs are designed specifically to reduce this type of noise, the NRR is based on the attenuation of continuous noise and may not be an accurate indicator of the protection attainable against impulse noise. Earplugs are better suited for warm and/or humid environments, such as foundries, smelters, glass works, and outside construction in the summer. Requirements related to attenuation include:
The employer must institute a training program for all employees with noise exposures at or above the action level and ensure employee participation.
Cultivate a vigilant attitude about hearing protection: Employees should expect their hearing protectors to slip or work lose over a period of time. Throughout their work shift, employees must periodically check to see if they need to readjust or refit their protector in order to maintain a reliable fit.
Guard against acquiring a false sense of safety: As the discussion and figures in this section have illustrated, it is easy to misuse hearing protectors and greatly reduce their effectiveness. Employees can be effectively protected from hearing health hazards if they:
Hearing protectors break and become worn: Employees also need to check their protector regularly and to seek repair or replacement whenever necessary. Lastly, they can help each other by encouraging their co-workers to use hearing protectors and to seek help when they have problems.
An effective hearing conservation program can prevent hearing loss, improve employee morale and a general feeling of well-being, increase quality of production, and reduce the incidence of stress-related disease.
The employer should administer a continuing, effective hearing conservation program whenever employee noise exposures are at or above an eight hour time-weighted average (TWA) sound level of 85 decibels or, equivalently, a dose of 50 percent.
As detailed in OSHA’s 1910.95 rule, the elements of an effective hearing conservation program are:
Employees who operate or maintain and repair the equipment are often the ones who know most about the processes involved. They need to express their concerns and ideas to management, the program implementer, or the noise-control engineer so that the noise-control devices will be as practical and effective as possible.
Sound levels often increase when equipment begins to wear or fails to receive appropriate maintenance. Also, changes in equipment placement may cause unintended effects on sound levels.
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