Temporaty Threshold Shift from Impulse

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Abstract
The need for a hearing damage risk criterion for repetitive discrete impulses of a type which occur widely in industry is discussed. The extension of the National Research Council Committee on Hearing, Bioacoustics and Biomechanics (CHABA, 1968) criterion to noises of this type leads to a discrepancy between the theoretical allowable limits of exposure and the experimental data, based on temporary threshold shift (TTS) studies. A laboratory experiment is described in which is considered the relationship between TTS and the exposure time, the number of impulses presented, and the pulse rate, using impulses of 127 dB peak sound pressure level and duration about 20 msec at pulse rates of 1·6, 3·2 and 6·4/sec. The growth of TTS, both with exposure time and number of impulses, is between logarithmic and linear, whilst change in pulse rate affects individuals differently, depending on their noise susceptibility. For the most susceptible persons the amount of TTS appeared to be dependent on the pulse rate, whilst for the less susceptible persons, TTS was largely independent of pulse rate for the particular rates used in this study.

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