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Noise Safety

The terms noise and sound are often used interchangeably, but the term sound is generally used to describe useful communication or a pleasant sound such as music; whereas the term noise is generally used to describe an unwanted sound which interferes with speech. Processes such as assembly equipment and air movement can generate excessive noise.

What Is Sound?
The sensation of sound is produced when pressure variations (amplitude) at a particular pitch (frequency) occur in a medium such as air or water. The quantity of the sound can be measured at the source to determine the effect on the ear.

How Is Sound Described?

The term used to describe sound pressure loudness is the decibel (dB). The higher the decibel number, the greater the sound pressure on the ear drum thus the louder the sound.
Pitch - Hertz (Hz) - a unit of measure for sound frequency. One Hz = one cycle per second. The more cycles per second, the faster the eardrum vibrates, the higher the sound pitch

How Does Hearing Work?

Sound is produced when pressure variations (amplitude or loudness) with a specific characteristic (pitch or frequency) reach the ear. The middle ear converts pressure variations into electrochemical activity in the inner ear which is transmitted, by the auditory nerve, to the brain for interpretation.

What Are The Hazards Of Noise?

Exposure to excessive noise levels can cause a number of responses from the worker including:

Irritability
Fatigue
Sleeplessness
Interference with Speech or the inability to hear alarms
Hearing Loss (Temporary, Permanent)

While irritability, fatigue and sleeplessness are indirect symptoms of exposure to excess noise which may not be readily identified by workers, interference with speech or the inability to hear alarms are symptoms more immediately noticeable to workers and thus can be identified rather quickly.
Hearing loss due to overexposure to noise can result in a ringing in the ear (tennitis) or a slight hearing loss for a short period of time (several hours) while the ear recovers. Continued over exposure to noise can result in permanent loss of hearing. The loss of hearing, whether it is temporary or permanent usually occurs at a frequency that is considered in the normal speaking / hearing range of 500 Hertz (Hz), 1000 and, 2000,4000, 6000 and 8000 Hz.

Methods to Control and Minimize Noise Exposure Hazards
Excessive noise levels can be minimized by using engineering controls, wearing some type of hearing protection, or using administrative controls.

Engineering Controls
The most desirable way to control excessive noise levels is by using engineering controls. The design of engineering controls must consider the sound pressure levels, type of noise (continuous or impact noise) and frequency of the noise. A number of applications may be considered to reduce noise levels including:

Absorption ­ Some materials, such as sponge or cork, may be porous enough to absorb noise.
Isolation - Isolating the source of noise with panels, or placing the equipment in another room to minimize the noise source.
Enclosure Barriers
Acoustic Dampening Materials - Some materials such as spray on acoustics can be applied to ceilings or walls around a piece of equipment to prevent noise from bouncing off solid surfaces and reverberating.
Replacing Equipment - Some equipment, because of its age, cannot be made quieter because noise levels were not considered during the development of the equipment thus the tool simply cannot be made quieter.
Modifying the Process - Some tools can be modified to add sound deadening insulation, or shock dampners to minimize the vibration which may cause the noise.

The advantage of applying an engineering control directly to a tool is that the one does not have to determine how to modify a room so that the noise levels can be controlled. Furthermore, applying engineering noise controls at the source removes the need for requiring workers to don protective hearing devices which when worn improperly can result in hearing loss.

Personal Protective Equipment

Hearing Protective Devices
The two types of hearing protective devices are ear muffs and ear plugs. Ear muffs fit directly over the ear and require very little adjustment. Ear plugs, on the other hand, must be properly fitted to the aural canal to be assured of a good fit. Areas requiring the use of hearing protectors must be properly marked.

Administrative Controls
This is the least desirable approach to minimize worker exposures to excess noise levels. Some administrative controls include adjusting the job schedule to minimize the time a worker is exposed to noise, or conducting the operation when other background or incidental noise is low.

Noise Exposure Criteria
SEMI S2
The SEMI S2 Guideline recommends that equipment be designed to control exposures to sound pressure levels equal to or greater than 80 dBA continuous or intermittent sound pressure level, and 120 dB instantaneous (impulse) sound pressure level.

Sound pressure levels in excess of 85 dBA requires a company to provide employees with hearing protection. In addition, audiometric testing must be performed on each of the workers who are exposed to excessive noise levels to monitor whether workers are suffering from hearing losses which is generally a progressive (chronic) problem.

OSHA Noise Standard

84 dBA or less-No hearing protection required
85-89 dBA - Hearing protection highly recommended
90 dBA or greater-Hearing protection is required at the workplace

Training
Workers who are required to wear hearing protectors must be trained how to properly wear them. In addition, workers must have a baseline audiometric test so that it can be determined if the worker is experiencing any hearing loss due to his work noise exposure. In addition, periodic monitoring of the work environment allows us to determine if the sound characteristics of the area have changed.