On a daily basis, workers are surrounded by sounds and noises. These exposures may be harmless, but long term exposure to loud noises may permanently damage hearing. Chain saws typically are measured at 125 decibels (dBA) and heavy equipment at 95-110 decibels (dBA). Continuous exposure to these levels may exceed the permissible amount allowed in Table G-16 of OSHA's Occupational Noise Exposure Standard [1910.95]. Even short term exposures to these levels can cause hearing loss.
Muffling and distortion of sounds and speech in a noisy environment.
Feeling of fullness in the ear.
Ringing in the ears (tinnitus).
A need to turn up the television.
Finding it difficult to talk on the phone.
Asking people to speak up when talking to you, and then complaining that they are shouting.
A need to look at a person while they are speaking (reading lips).
Engineering controls are the best long-term solution to the occupational noise problem. As required by 1910.95(b)(1), feasible engineering or administrative controls must be utilized whenever employees are subjected to noise exceeding the levels listed in Table G-16.
Noise problems can be divided according to three traditional methods of control:
Other approaches to noise control include:
After engineering controls have been installed, the noise reduction that was obtained should be quantified. This evaluation may be necessary to show compliance and may be useful in solving future noise problems.
The preferred method of engineering control is noise reduction at the source.
Methods of machine control include:
- isolating it to prevent the radiation of vibration,
- putting on a muffler,
- reducing the driving force, response, and area of the vibrating surface, and
redesigning the machine or work process.
Design for quiet can be built into a company's specifications for new machinery, avoiding the trouble and expense of retrofitting old equipment.
Source control may eliminate the requirements of hearing protection, audiometric testing, and/or limitation of exposure time.
Controlling the source may also improve speech communication and reduce annoyance.
High frequency noise is very directional and is relatively easily reflected or blocked by any type of barrier.
The wavelength of a 16-kHz tone, for example, is about ¾ inch, so a barrier of 1 to 2 inches higher than the source is generally sufficient to reflect noise of approximately the same frequency away from a nearby worker.
Methods of controlling the transmission (or path) of sound include:
- using mufflers,
- placing absorbent material on the ceilings,
- erecting barriers, and
- hanging lead curtains around a noisy area.
The method of controlling nose exposure at the receiving end usually means removing the affected person from the sound field. However, treating the receiver's immediate environment may also involve:
- erecting an enclosure or control booth around the employee, and
- implementing hearing protection devices such as ear muffs or ear plugs.
In a practical approach, the following items must be determined successively to accomplish noise control:
Noise criteria for each occupied space.
Sound power level of the noise produced by each source.
Noise levels at typical employee positions in that space.
Attenuation of the noise by walls, ducts, etc., between each source and the space in question.
Required additional attenuation (item 3 minus item 1).
Identify major noise sources and select noise control treatment.
Any special mounting of the devices necessary to control flanking noise.
Any vibrating elements whose movements may be transmitted to some other component, causing it to become a noise radiator.
Another approach to noise control, one that OSHA give equal status with engineering controls, is the use of administrative controls. An administrative control may include rotating workers between noisy and quiet jobs (or more often noisy and less noisy jobs).
- This practice is not as widely used as engineering controls.
The final result tends to be that many workers develop small hearing losses rather than a few workers developing big ones.
One thing employers can do to diminish the problem (although it is not a complete solution) is to provide workers with rest and lunch areas that are sufficiently acoustically treated to provide the ears with enough quiet to provide some recovery from temporary threshold shifts (TTS).
The only completely satisfactory solution is to reduce exposures to safe levels (8-hour time-weighted average levels below 85 dB).
The general industry noise standard states that the employer must administer a continuing, effective hearing conservation program whenever employee noise exposures are at or above an 8-hour time-weighted average (TWA) of 85 dBA or, equivalently, a dose of 50%. [1910.95(c)(1)]
- This measure is referred to as the action level. [1910.95(c)(2)]
- Employee noise exposures do not consider any attenuation provided by the use of hearing protection.
Refer to 1910.95 Appendix A for instructions and additional information on computing employee noise exposures.
The function of the hearing conservation program is to protect workers with significant occupational noise exposures from suffering material hearing impairment, even if they are subject to such noise exposures over their entire working lifetimes.
An effective hearing conservation program can do more than prevent hearing loss. It can improve employee morale and general feeling of well-being, increase quality of production, and reduce the incidence of stress-related disease. It is important for workers to understand the reasons for the hearing conservation program's requirements, as well as the need to protect their hearing, in order to increase the likelihood that they will become motivated to participate actively in the program.