Forensic Acoustics Case Study

INITIAL INVESTIGATION

Measurements of sound in the areas where the employees transacted their business and waited for the truck loading to be completed revealed levels in the mid- to high 70 dB(A) range. The employees spend approximately two hours at this location before leaving on deliveries.

The relatively low level of the noise exposure prompted us to ask for a sample of audiograms of the claimants for further analysis. As the noise exposures were so low, we wanted to know hat thresholds were shown by some of the claimants. The attorneys provided a sample of eighty audiograms.

Conparison of Hearing Threshold with Standard
The second figure shows a comparison of the threshold of an employee in this case with the thresholds predicted for the population by the standards. We found that the hearing levels claimed by the employees did not all show a typical 3KHz notch pattern for NIHL were substantially more severe than would be predicted for the measured noise exposures.

Distribution of Hearing Levels
A further discrepancy was found in the hearing thresholds themselves. The employees ranged in age from 26 years to over 70 years old. All the hearing thresholds however, fell within approximately 10 dB of one another. For this range of ages, considering different sensitivities of individuals to noise and different rates of development of presbycusis, a range of 40 dB would be more typical.