Critique of "An Analysis of the Blast Overpressure Study Data Comparing Three Exposure Criteria", by Murphy, Khan, and Shaw

Report No. ARL-CR-657
Authors: G. Richard Price
Date/Pages: August 2010; 36 pages
Abstract: Murphy et al. analyzed the performance of MIL-STD-1747D, LAEQ8, and the Auditory Hazard Assessment Algorithm for Humans (AHAAH) model as they predicted outcomes on the Albuquerque studies (AS) data set. Unfortunately, they erred in several invalidating ways. First, they overlooked underlying nonlinearities in the hearing protector (which rendered the AS data set unique, the use of MIL-STD-1474D invalid, and the LAEQ8 calculations useless outside the data set). They overlooked the nonlinear conductive path of the ear that, at the very high intensities, greatly affected the energy reaching the cochlea (which implies that their LAEQ8 analyses measured under the muff cannot be usefully extrapolated outside the data set). Their analysis of LAEQ8 under the protector did establish that a criterion level of 110-dB LAEQ8 fits the data, but they failed to comment on the discrepancy between this level and the 85-dB LAEQ8 criterion that is traditionally used. Further, they misapplied the AHAAH model in using the "unwarned" calculation and overlooked the model's capacity to predict the effect on different percentiles of the population. Their analysis indicated that the "warned" calculation with the AHAAH model did rank hazard acceptably for the 95th percentile ear, and we note that it did so for small arms fire as well, all without adjustment. More research in the pressure regime between 115 and 160 dB is needed for the development of a comprehensive damage risk criterion for intense noise.
Distribution: Approved for public release
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Last Update / Reviewed: August 3, 2011