Evaluating the Quality of Hearing Conservation from Hearing Test Results

Often I am asked the question, "What information may be gleaned from the plant hearing testing that would indicate the quality of our hearing conservation program?"

It is important to separate successful hearing conservation from recording hearing loss on the OSHA 300 Log. 1910.95 requires monitoring of hearing change using a Standard Threshold Shift (STS). This is defined as a change in hearing of 10 dB average at the frequencies of 2, 3, 4 K Hz in either or both ears. Additional loss is acceptable when using the aging tables presented in the appendix of the standard. A 30-day calendar retest is allowed. If loss is confirmed with a retest, or if the 30-day period passes without a retest, then the loss is considered confirmed. The occurrence of an STS triggers a set of actions by the company commonly called "STS follow-up". This consists of notifying the employee in writing of the change, recalculating the attenuation of their hearing protectors to be sure they have adequate protection, fitting and/or refitting hearing protection, and enforcement of wearing hearing protection.

In a separate regulation, OSHA recently (January 1, 2003) defined the criteria and procedures for identifying and entering changes in hearing on the OSHA 300 Log. They tied the change in hearing to the occurrence of an STS as defined in 1910.95. However, several additional qualifiers were added. The change is not recordable if the loss is within the range of normal hearing. Nor is the loss recordable if an audiologist or physician determines on a case-by-case basis that the change is non-occupational.

Three types of identified changes
Therefore, within the hearing test data there are three types of identified changes. 1) An STS defined as a 10 dB average change at 2, 3, 4 K Hz without aging. This is called an Early Warning Shift. 2) An STS with aging, which is used to initiate an STS follow-up. 3) An STS that qualifies as an OSHA Loggable.

Best program quality indicator
The best indicator for the quality of the hearing conservation program in terms of preserving hearing is the Early Warning Shift. This measure is sensitive to changes of a total of 30 dB at the frequencies of 2, 3, 4 K Hz. It will identify employees with a minimal change. By monitoring these employees to be sure they are wearing hearing protection and wearing it correctly, the company may prevent noise induced hearing loss and avoid future STS’s with aging and OSHA recordable shifts. It should be noted that in a plant with an aging population (50 plus), the Early Warning Shift goals may not be possible to meet. Certainly that does not mean we should not try and work more diligently with this vulnerable population.

If the only cause of hearing loss was noise or aging, the task would be easy. However, hearing loss may occur for many different reasons. Every cause of hearing loss is present in the general population and testing employees in a plant constitutes testing the general population. It is expected that some 3% of the population will have significant change in hearing without noise. Age is the biggest agent, however the Standard adequately allows for aging changes by adding to the 10 dB average change from the aging charts presented in the Standard. Noise is another significant agent and plant workers are at high risk for noise exposure. In most cases it is possible to determine if a work-related or non-work related change has occurred, and therefore determine that the employee’s change is not loggable, however, it is impossible to determine in every case of change that noise did not aggravate, contribute or cause an individuals hearing loss.

The table below may be healthful in assisting plant safety managers and management in determining the success of their program.

Expectations for the hearing conservation program should be realistic and obtainable. Ideally, no hearing loss resulting from noise exposure is acceptable, however, it would be rare not have any STSs or Loggables in a plant of 200 employees. A 1% change would be 1 person out of 100.

Many times our attention is on the wrong end of the process. Rather than committing a great deal of time and money towards efforts to prevent possible OSHA recordables from being recorded, program focus is better spent on identifying the Early Warning Shift and monitoring their noise exposure and the wearing of hearing protection. With good testing, audiological review, availability of properly fitted hearing protection, enforcement of wearing hearing protection, and hearing conservation education, the recordable loss issues will diminish significantly.