Prevention of noise-induced hearing loss in the Canadian military.

A prospective study was undertaken to investigate the development of noise-induced hearing loss in Canadian military recruits, and to assess the effectiveness of the hearing conservation program currently in place. The participants were 134 men and women, 20 to 30 years of age, employed in four trades, three of these (infantry, artillery, and armour) associated with high noise levels. The data comprised audiometric measurements made at the time of entry and after 3 years of employment, and responses to a questionnaire mainly relating to noise exposure in the workplace and during leisure activities, and the utilization of personal hearing protective devices. The findings showed that group audiograms at entry and at the 3-year recall were characterized by a 6-kHz notch that was indicative of noise-induced hearing loss, although mean threshold values were within normal limits. By the 3-year recall, 11% of the infantry had sustained a mild-to-moderate hearing loss in the left ear, greater than 25-dB HL, that was consistent with the use of small-calibre weapons. Responses to the questionnaire indicated that, while subjects appreciated the potential benefit of wearing hearing protectors, instructions in their proper use and education on the hazards of noise exposure were poor. The results suggested methods to strengthen the existing scheme for hearing conservation to further minimize risk.