Page 98 - Master Handbook of Acoustics

listening. Over time, it is possible that patterns will emerge that will provide correlation. Though
correlation is desirable, critical listening plays an important role without it.

Occupational and Recreational Hearing Loss

Hearing damage is a serious occupational hazard. Factory workers, truck drivers, and many others
are subject to noise levels that are potentially harmful. Over time, with repeated exposure, hearing
loss may occur. Audiologists determine what noise exposure workers are subjected to in different
environments. This is not easy because noise levels fluctuate and workers move about; wearable
dosimeters are often used to integrate the exposure over the work day. Companies often install noise

shields around offending equipment and mandate ear plugs or ear muffs for workers.
The hearing of workers in industry is protected by law. The federal Occupational Safety and
Health Administration (OSHA) in the Department of Labor maintains noise exposure limits in the
workplace. The higher the occupational noise, the less time of exposure is allowed. Noise exposure

is measured in daily noise doses for an 8-hour day. Table 4-2 lists the permissible daily noise
exposure, measured with the slow response of a standard sound-level meter. The maximum allowed
dose is 100% of the daily limit. A dose is calculated as the time a worker is exposed to different
noise levels, relative to the maximum exposure time permitted at that level. For example, a worker
may be exposed to a maximum of a 90-dBA noise for 8 hours, a 100-dBA noise for 2 hours, or a 115-
dBA noise for 15 minutes. When the daily exposure is due to two or more noise levels, the total noise
dose is given by:

TABLE 4-2 OSHA Permissible Noise Exposure Times