Rigor Required for a Re-Examination of Exchange Rate for Occupational Noise Measurements Re : Dobie , R . A .

488 The recent article by Dobie and Clark (2014) on “Exchange rates for intermittent and fluctuating occupational noise: A systematic review of studies of human permanent threshold shift” aimed to compare the suitability of a 3-dB versus 5-dB exchange rate (ER) in predicting hearing loss from nonimpulsive intermittent or fluctuating noise exposures by reviewing studies of human noise-induced permanent threshold shift. The authors concluded that 3-dB ER systematically overestimates the risk of noiseinduced hearing loss for intermittent or fluctuating noise. We contend that the authors did not arrive at their conclusions through an appropriate investigation. The article used flawed methodologies in the treatment and analysis of the data/studies and drew conclusions that were not substantiated by the cited data. The authors indicated that their review did not aim to make recommendations for the regulation of occupational noise but suggested that their review provided evidence for a re-examination of recommendations in their concluding remarks. The National Institute for Occupational Safety and Health (NIOSH) maintains its recommendation of the 3-dB ER to provide sufficient protection for the many variations of continuous, intermittent, and fluctuating noise exposure scenarios encountered in the workplace. In view of the advances in noise measurement and the studies’ other weaknesses, we question the suitability of revisiting a narrow segment of the human evidence (excluding robust animal studies and temporary threshold shift studies) based on outdated methodologies to address such an important issue. The most appropriate ER for predicting hearing loss from noise exposure varies based on the level and duration of the noise. In fact, the 1966 and the 1993 reports by the National Research Council Committee on Hearing, Bioacoustics, and Biomechanics (CHABA) on damage-risk criteria for noise observed that ERs from 0 to 11 dB best fit the damage caused by longversus short-duration exposures. In addition, exposures of higher frequency spectra necessitated smaller ERs (Kryter et al. 1966; National Research Council [NRC] 1993). Fluctuating and intermittent noise exposures have long been recognized as producing less hearing loss due to the physiological recovery of the auditory mechanism during quiet periods; however, a correction for intermittency has been difficult to define because the protective effect varies based on a number of variables including the spectral content of the noise, the noise level during the “quiet” period, and the interval between exposures (Suter 1992). None of these variables were available in the studies selected by Dobie and Clark nor are we aware of any studies that have sufficiently evaluated the interaction of these variables.