Many governments require or mandate hearing conservation programs for workers in industries and in other occupations in which hazardous noise conditions exist. Hearing conservation programs are designed to protect workers from the effects of hazardous noise environments.
Most nations have dictated specific obligations at an action level which corresponds to a dose of 50% of the PEL. Therefore, the OSHA TWA A‐weighted action level is 85 dB [31]. The equivalent NIOSH A‐weighted action level is 82 dB [22].
At these action levels, regulations require implementing hearing conservation programs.
In general, a hearing conservation program will have at least the following components: noise measurements, the use and care of hearing protection devices, audiometric testing, employee training and education, and record keeping.
Hearing evaluation through audiometric testing is a key component of a hearing conservation program. If employees are working in areas with intense noise levels, it is necessary to monitor their hearing regularly. These hearing tests will help in determining whether or not the administrative and engineering controls and ear protection devices are being adhered to or effectively used. The OSHA 90 dB eight‐hour workday limit for the A‐weighted sound pressure level only protects a certain percentage of workers (about 93%). Since people’s ears are different, some workers (about 77%) will still be suffering appreciable hearing damage in these conditions. Through audiogram results it may be possible to identify individuals with higher than average susceptibility to noise‐induced hearing loss (those with “tender” ears). An individual could adhere to the limits of the more conservative occupational noise recommendations and still develop hearing loss due to individual risk factors.
In fact, NIOSH recommendations for a hearing loss prevention program make it mandatory to conduct audiometric tests periodically on all individuals whose A‐weighted exposures equal or exceed 85 dB as an eight‐hour TWA. It is recommended that the tests should be conducted annually and baseline audiometric tests shall be conducted before employment (conducted upon the initiation of noise exposure) or within 30 days of employment for all workers who must be enrolled in the hearing conservation program [22].
It is extremely helpful to use an educational program to teach management at all levels and all shop personnel an industrial plant the facts concerning occupational hearing loss, noise control, and ear protection devices. With the commitment and example of management, after introducing such a program, the majority of shop personnel will cooperate with a hearing conservation program.
More stringent occupational noise legislations establish that if action levels are exceeded, immediate engineering noise control measures must be implemented within a 6–12 month period as part of a hearing conservation program.
Protection can be provided not only by use of engineering controls designed to reduce the emission of noise sources, control of noise and vibration paths, labeling of noisy areas, and the provision of HPDs, but by the limitation of personnel exposure to noise as well. For instance, arranging for a machine to be monitored with a control panel that is located at some distance from a machine, instead of right next to it, can reduce personnel noise exposure. The rotation of personnel between locations with different noise levels during a workday can ensure that one person does not stay in the same high noise level throughout the workday. Reference [43] describes hearing conservation programs and, in addition, some legal issues including torts, liabilities, and occupational injury compensation.
EXAMPLE 5.6
As part of a hearing conservation program following the OSHA criteria, we need to determine the maximum time for which a worker may spend in a particular workshop where the A‐weighted noise level is 105 dB without using HPD. The rest of the eight‐hour working shift the worker is subjected to a constant A‐weighted level of 85 dB.
SOLUTION
According to Table 5.3 or Eq. (5.3) the exposure to A‐weighted sound pressure levels of 105 and 85 dB is allowed for 1 and 16 hours, respectively. Since the total dose must be less than 100% and if the worker is exposed to 105 dB for t hours and 85 dB for (8‐t) hours, then, 1 = t + (8‐t)/16. Solving for t, we obtain t = 0.53 hours or 32 minutes. Therefore, as an administrative measure, the worker should be allowed to work less than 32 minutes in the workshop with high noise level to comply with OSHA.
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