Abstract : The U.S. Army needs realistic safe limits for exposure to impulse noise produced by heavy weapons. Impulse noise limits, based on data from small arms, may be overly conservative. In order to define new limits for heavy weapons, this systematic 5-year study of the effects of high-intensity impulse noise on human volunteers was undertaken. The number of impulses, the peak pressure levels, and spectral distributions of energy of heavy weapon-like impulses were varied systematically. Five major groups of 273 volunteers were given a series of exposures to one of three impulse types and to three types of hearing protection. The impulse spectrum was varied by changing the distance between the volunteer and an explosive detonation. The peak pressure level was varied in 3-dB steps by changing the weight of the explosive charge. The number of impulses per day was 6, 12, 25, 50, or 100. Volunteers wore hearing protection for all exposures. After each exposure, the amount of TTS, if any, was determined. Each volunteer started with an exposure of six impulses at the lowest intensity. If the TTS was less than 15 dB, the subject received six impulses at the next higher level the next day. Noise induced hearing loss, Temporary threshold shift of hearing(TTS), RA III, Volunteers.