 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
 |
 |
|
||||||||||||||||||||
 |
|
||||||||||||||||||||||
 |
 |
|
|||||||||||||||||||||
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
|
|||||||||||||
 |
 |
|
|||||||||||||||||||||
|
|||||||||||||||||||||||
 |
 |
|
|||||||||||||||||||||
 |
|
||||||||||||||||||||||
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
|
|||||||||
 |
|
||||||||||||||||||||||
 |
 |
|
|||||||||||||||||||||
Hearing Conservation
What are the effects of noise?
Hearing loss from noise causes the deterioration of hair cells within the inner ear (cochlea). Chronic noise exposure will cause irreversible and generally medically untreatable hearing loss. Sometimes an acute noise impact or blast injury will recover to some degree. The high frequency sounds are affected first, and this usually can be seen at 4000 Hz on audiometric studies. If noise exposure continues withouds it appropriate protection, both high and low frequencies will be affected. The high frequencies are significant for speech understanding, and contain soft consonants of speech; some examples are “sh,” “th,” “p,” “t,” and “k”. Low frequency sounds include “g,” “m,” “b,” and the vowels. Speech discrimination (word understanding) will therefore be gradually affected from chronic noise exposure.
With exposure of loud sounds (like a concert) some people can experience a temporary threshold shift (TTS). This is a feeling of diminished hearing and it is usually associated with aural (ear) fullness and tinnitus. Typically, the symptoms resolve by the following day. Repeated exposures, however, may result in a permanent hearing loss with tinnitus.
Evidence has also demonstrated that a number of chemical agents used in industry are toxic to the hair cells. They may even be more dangerous when they occur in combination with noise. For example, some of these substances include toluene, chlorine gas, trichloroethylene, and carbon dioxide.
Elements of a Hearing Conservation Program
One of the most important aspects of a hearing conservation program in the workplace is the measurement of noise in the environment in which employees are placed. It determines the level of noise to which employees are exposed and whether they need to be enrolled in the Hearing Conservation Program. It is important to determine if a hearing loss exists prior to an employee beginning work, and if a loss is present, to establish a cause. As the employee continues to work in a hazardous industrial noise environment, audiograms need to monitor the hearing level annually. The annual audiograms are the basis for determining if any hearing has been lost while employed. The patterns of the loss can also determine the work relatedness of the loss. Therefore soon after beginning employment, the employee needs to have a valid baseline audiogram against which subsequent audiograms can be compared. The baseline testing should be performed only after the employee has been in a noise free environment at least 14 hours. At least annually, after obtaining a baseline audiogram, the employee will need a follow up hearing test if exposed at or above a noise level of 85 dB SPL for an 8-hour day. If the annual audiogram demonstrates an employee has lost hearing, usually a retest is performed within 30 days. Further evaluation is often required to determine if the loss is caused by occupational noise, or unrelated to the workplace. If a unilateral loss has occurred, further testing is required to rule out other causes for the progressive hearing loss occurring in only one ear.
The employer is required to provide the employee with:
- a copy of the requirements for hearing conservation
- the baseline audiogram and the most recent hearing test
- measurements of background sound pressure levels in the audiometric test room
- a record of audiometer calibrations
If the follow up hearing test demonstrates a standard threshold shift, the employee:
- if not wearing hearing protection will be fitted with hearing protectors and trained in usage.
- if already using hearing protectors, will be refitted and retrained, and given protectors with greater attenuation if needed
- will be referred for an otological examination, if addition testing and evaluation is necessary