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Exposure limits for airborne sound of very high frequency and ultrasonic frequency

This document considers the subjective and auditory effects of audible sound in the very high frequency range (10-20 kHz) and also in the inaudible ultrasonic range (greater than 20 kHz). A number of Damage Risk Criteria and Maximum Permissible Levels were first recommended by individual researchers in the 1960s. These provisional recommendations, supported by limited experimental and survey data, were then adopted by national and international bodies. The exposure limits were published with the intent of avoiding any subjective effects and any auditory effects, in any exposed individuals. At present, the exposure limits lack the sophistication to predict hearing damage and adverse subjective effects caused by sounds outside the customary frequency range for occupational noise exposure assessments.