Health Hazard Assessment for Blast Overpressure Exposures Subtitle - Evaluation of Impulse Noise Criteria Using Human Volunteer Data

摘要

The evaluation of impulse noise criteria is becoming more critical as many new weapons exceed exposure levels for single hearing protection set forth by the MIL-STD-1474D. Previous man-rating studies have consistently shown that auditory injury does not occur at these levels. Consequently, there is general belief that the current standards under predict the threshold at which injury occurs. Four impulse noise auditory injury criteria adopted by NATO countries, namely, the MIL-STD-1474D (USA), Pfander (Germany), Smoorenburg (Netherlands), and L(Aeq8) (France), are evaluated against human volunteer data. Four data sets from subjects wearing single hearing protection exposed to increasing blast overpressure effects were obtained from tests sponsored by the US Army Medical Research and Materiel Command. Two data sets were obtained from free field and bunker tests using RACAL earmuffs modified to simulate poor fitting. Two other data sets came from the M198 howitzer and Viper man-rating studies using EAR earplugs. Injury threshold was taken as a temporary threshold shift (TTS) >/- 25 (3) at any frequency. Using logistic regression, the four criteria were each correlated with the test data. The analysis shows that all four criteria are overly conservative by 4-12 (3). The MIL-STD-1474D for single hearing protection is 9.9 lower than the 95% protection at 95% confidence band for this particular group of subjects. Similarly, the thresholds for 95% protection at 95% confidence for Pfander, Smoorenburg and L(Aeq8) are 195.9, 203.2 and 114.7 (3) respectively with single hearing protection. These results can help guide a revision of the criteria for impulse auditory injury.