To develop realistic requirements for impulse noise measurement at the job site, surveys were conducted to determine the contributions of the impulsive component to total exposure for a worker. At 15 facilities engaged in processes producing impulse noise, surveys included measurement with ban widths from 10 Hertz (Hz) to 40 kiloHertz (kHz) with a dynamic range of minus 72 decibels (dB). This was done by direct digital recording of the waveform. Peak and equivalent noise levels, the power spectrum, and dose were analyzed over several repetitions of the process cycle. Intervals containing the impulse noises were compared to the total duration of exposure and the total dose. All processes examined exhibited power spectra with dominant low frequency energy below 12kHz, and usually below 2kHz. The equivalent levels for the impulsive noise, measured over several process cycles, was within 35dB of the peak levels. For a 5dB exchange rate, noise intervals contributing to impulse noise often contributed less than 20 percent of the total duration of the exposure while providing 50 percent of the total dose. At a 3dB exchange rate, the relative contributions were even more disproportionate. The author concludes that the noise is adequately classified by the peak of its amplitude distribution. Until impulse noise is classified according to industry and hazard, a 3dB integration with a 5dB correction factor is an appropriate and conservative figure.
Division of Biomedical and Behavioral Science, NIOSH, U.S. Department of Health and Human Services, Cincinnati, Ohio, 8 pages