Guidelines for environmental impact statements on noise (airblast)

Guidelines for preparing environmental impact statements on noise were recently assembled and submitted for agency reviews. Acousticians have made considerable progress in unifying their concepts for prediction, measurement, and assessment of injury and annoyance resulting from many kinds of continuous tone noises. There have also been numerous attempts to transform impulse type noise parameters into regular acoustic terms, particularly for evaluating explosion waves and sonic booms. For low overpressures from explosions, well below the eardrum injury threshold of 35kPa (5 psi), environmental concern is primarily with minor damage thresholds, rather than annoyance from single events or events widely spaced in time. Low frequency components cannot be ignored in this context, so a compromise has been reached in the guidelines. Blast wave analyses, rather than acoustic analyses, will be made when sound pressure levels above 140dB (200Pa, 0.03 psi overpressures) are expected. A conservative evaluation, relating an explosion yield limit to exposed population and distance, has been developed to allow simple decision-making, regarding the analysis system to be used. This paper describes the derivation of this yield-limit relationship.