To the Editor: Recent research shows that the prevalence of noise-induced hearing loss (NIHL) is not restricted to industry. Excessive noise levels exist in nonindustrial occupations. For example, cases of NIHL have been found in firefighters,1 hospital employees,2 musicians,3,4 and police officers (Lankford JE, West D: Hearing sensitivity of polic officers [poster session at the 1992 annual conference of the National Hearing Conservation Association, San Antonio, TX, 1996]). There is evidence that noise is widespread in educational settings as well (Jiang T: Noise measurement and analysis of the gymnasium at St. Charles Elementary School [internal report, Halifax, NS, Canada, 1996]).5-8 Poor acoustic conditions reduce speech intelligibility in classrooms. Noise makes teachers uncomfortable and can also be detrimental to their work. Furthermore, research has found that noises associated with certain educational activities, such as music teaching and vocational training, can become hazardous to the hearing of both students and teachers. In 1997, Jiang and Tompkins9 reported a case in which a young female music teacher developed NIHL from her long hours of loud music exposure.
At schools, one of the frequently reported noise sources is in gymnasia. In 1990, Hetu et al5 conducted a series of noise measurements in eight school gymnasia in Quebec, Canada. They found that the median LAeq was 83 dB, with the maximum peak levels exceeding 115 dB. In 1996, Jiang (Halifax, NS, Canada, 1996) surveyed noises in an elementary school gymnasium. The LAeq was 94.4 dB for the teacher, and the peak level reached 125 dB. The average noise levels obtained from dosimeters worn by six students varied between 88 dBA and 99 dBA.
Although there is a growing concern with noises in school gymnasia, cases in which physical education teachers are at risk of NIHL are rare. Recently, I presented a unique case of a 51-year-old physical education teacher who was diagnosed with a permanent hearing impairment. His hearing loss is believed to be caused by his 27 years of teaching at schools. For details, please refer to the Journal of the Acoustical Society of American10 and the proceedings of the 1997 NOISE-CON.11 What is worth mentioning in this letter is that besides the strong correlation between the noise data of the gymnasium (Table 1) and his hearing loss, whistle sound has been identified as a major etiological factor.
During the noise study, it was noted that blowing a whistle generated the highest noise level. Considering the fact that whistles are commonly used by physical education teachers in gymnasia, it is important to find out sound levels of whistles so that their potential risk can be accurately assessed. Interesting enough, in 1996, Nigro and Warrick12 reported a case of NIHL caused by whistles in this journal. They found that whistles generated over 125 dB peak sound pressure level at 2500 Hz in the open sound field. Because the noise sources (whistles) are very close to the ears, the actual whistle sound reaching tympanic membranes should maintain much of its energy. More importantly, because whistle sound has a very narrow bandwidth (near 3000 Hz) while entering the external ear canal, it may be further amplified by the external ear resonance effect. Thus sound field data may not be able to realistically describe the important interaction between whistle sound and the external ear canal in terms of the effects on the hearing. Therefore, in my study, a real-ear measure was conducted to record the in situ sound levels and spectral characteristics of whistles. An ACME whistle was selected because it was approved by 41 countries. A probe microphone was inserted into the external ear canal of the experimenter at 6 mm in front of the tympanic membrane. While the whistle was being blown, a real-time fast Fourier transform (FFT) analysis was performed. The results are presented in Figure 1.
Clearly, my data is consistent with that of Nigro and Warrick in that the whistle was a narrow-band sound centering at 3150 Hz. Nevertheless, the in situ peak sound pressure level was 5 dB higher than that measured in the sound field. This difference is of great significance. In acoustical terms, the energy at the tympanic membrane, in this case, has actually doubled, thus posing a much greater risk to the hearing of the whistle user. It is also worth mentioning that there appears to be a strong correlation between the spectral pattern of the whistle and the configuration of the patient's hearing loss. According to the ½-octave shift theory,13 the frequency of the hearing threshold shift tends to occur approximately ½ octave higher than that of the offending noise. In this case, the patient has a bilateral NIHL evidenced by a notch at 6000 Hz, as indicated in Figure 2. Therefore, it is reasonable to conclude that the 3000 Hz narrow-band whistle was one of the major etiological factors contributing to his 6000-Hz notched hearing loss.
Finally, it is my belief that there is an urgent need to explore this issue. A large-scale demographic study on the prevalence of NIHL among physical education teachers and other professional whistle users should be initiated. The outcomes will determine whether hearing conservation programs should be provided.
Tao Jiang, MSc
Nova Scotia Hearing and Speech Clinic; Halifax, NS, Canada
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13. Henderson D. Effects of noise on hearing. In: Feldman AS, Grimes CT, eds. Hearing Conservation in Industry.
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