Looking for information on basic audiology terms? We've put together a simple glossary of basic terms.
When a shift in hearing occurs, it is not immediately known whether that shift is due to noise exposure, normal age-related hearing loss, disease or even wax blockage. In many ways, age-related hearing loss mimics noise-induced hearing loss: it is painless, gradual in progression and affects high frequencies. To help differentiate the effects of aging from noise, OSHA published age correction tables within its Hearing Conservation Amendment. These age correction tables [one for males, one for females] show relative age correction values between to ages. Use of age corrections is optional for Hearing Conservation Program managers, but their use definitely helps differentiate the contributions of aging from noise in a hearing loss.
A standardized hearing test. According to regulations, workers in a Hearing Conservation Program are required to receive an audiogram on a periodic basis. This hearing test is compared to the worker’s baseline audiogram to determine if a significant decline in hearing has occurred.
The baseline hearing test to which all successive hearing tests are compared. A worker’s first hearing test is usually his reference audiogram. But in some cases, the medical professional reviewing the audiograms may revise the reference, by designating a later hearing test to be more indicative of stable hearing levels. A reference audiogram might be revised due to improved thresholds [if the employee undergoes corrective surgery, for example, for a physical disorder in the ear] or due to worse thresholds.
Permanent loss of hearing due to overexposure to noise. NIHL is marked by a decline in high-frequency hearing sensitivity [often beginning around 3000-4000 Hz] regardless of the noise source, usually bilateral [affecting both ears], and usually slow in progression – NIHL often takes years to develop, not days or weeks. NIHL is often accompanied by tinnitus [ringing in the ears], but is not typically accompanied by other symptoms such as pain, fullness, or drainage from the ears. NIHL is permanent, painless, progressive, but also very preventable when hearing protectors are properly used 100% of the exposure time.
A permanent decline in hearing following overexposure to noise. PTS usually occurs after repeated exposures to loud noise, but can also occur after only one traumatic exposure to noise. Most workers experience a Temporary Threshold Shift in hearing prior to a Permanent Threshold Shift. But because of individual variations in tolerance to noise, there is no way to predict when a shift in hearing will become permanent. Therefore, hearing protection is critical for all loud noise exposures.
The amount of decline in hearing that triggers required reporting on OSHA health and safety records. Current criteria for recordability on OSHA’s Log of Work-Related Injuries and Illnesses [OSHA Form 300] define a hearing loss as recordable when any work-related Standard Threshold Shift occurs, and when the resulting average hearing thresholds are 25 dB HL or higher at the STS frequencies in that ear [2000, 3000 and 4000 Hz on the audiogram]. This means a hearing loss is recordable when a significant noise-induced shift in hearing occurs, and when that shift is out of the normal range of hearing.
OSHA Form 300: http://www.osha.gov/pls/publications/pubindex.list#300
A significant change in hearing thresholds, defined by OSHA as an average decline of 10 dB or more at 2000, 3000, and 4000 Hz in a given ear, relative to a baseline audiogram. A Standard Threshold Shift can only be determined when at least two audiograms for the same worker are compared – the baseline and the annual audiograms. Optional age corrections can be applied when determining whether an STS has occurred. When an STS occurs, employers are obligated under OSHA regulations to inform the worker, and carry out a series of preventive measures to reduce the employee’s noise exposure and refit/retrain the worker in hearing protection.
Initial overexposures to noise cause a temporary decline in hearing, which may last for a few minutes or hours. A worker with a Temporary Threshold Shift will perceive incoming sound as being muffled, or not as sharp; but once the ear has rested for some time, hearing recovers to normal levels. Physiologists believe the receptor cells in the ear fatigue with loud noise exposures, and require several hours of relative quiet to return to their normal state. Repeated overexposures to loud noise, however, cause permanent damage, from which the ear cannot recover [see Permanent Threshold Shift]. Since different people have varying tolerance for TTS, there is no way to predict when a temporary shift in hearing starts to become permanent.
Persistent ringing in the ears. Tinnitus is a common aftermath of receptor cell damage in the inner ear due to overexposure to noise. In response to that damage, the brain generates its own sounds, which are routed back to the ear and perceived as ringing [or sometimes as hissing or buzzing]. Tinnitus in its earliest stages may be seen as a warning sign of overexposure to noise. In its later stages, it is annoying and disturbing, and though treatment options are limited, sufferers should seek medical advice for possible help from an audiologist or physician.