噪音劑量與暫時性聽力閾值變化之關係探討

The Dose-Response Relationship with Noise-Induced Temporary Threshold Shift(NITTS)

本研究係採取實驗室設計來比較美國職業安全衛生署（OSHA）和國際標準組織（ISO）不同噪音曝露進階何者較能預測國人聽覺特性。本研究所選取之研究對象為31位聽力正常之大學生，使其重複曝露於80-95 dB SPL工廠噪音。每次曝露時間為30分鐘，並且於曝露前先測其聽覺閾值，作為基線值。再於每次曝露後2分鐘始測其聽覺閾值（即TTS2）。另外，在恢復時間方面（recovery time），是測95 dB音量30分鐘曝露後2、40、60、80分鐘，觀察聽力恢復的情形。在結果可看出OSHA和ISO隨音壓位準的增加，聽力在高頻（4000，6000 Hz）損失有逐漸增加，且呈現V字型，4000 Hz為最低點。在恢復時間方面，語音頻恢復較快，聽力在4、6K Hz恢復較慢，曝露後2分鐘聽力損失達到最大，80分鐘時才恢復至基線值。依據Reed-Muench method計算ED50值，做為曝露音量預測聽力損失系統所需之理論發展與實驗數據。由本研究可知在OSHA標諄聽力在4000 Hz只要83.8 dB就有一半的人暫時性聽力損失10 dB或以上，所以短期高噪音的曝露也是不可忽視的影響。本研究計算出critical level為77.9 dB SPL，其實並非要高噪音量才會造成聽力損失，最好能在critical level應實施勞工聽力保護教育，並能盡量避免噪音曝露。在ISO標準和OSHA標準的比較方面，本研究結果是比較符合ISO標準，聽力傷害是與所接受聲音能量的作用成比例。本研究能量加倍時，聽力損失是呈現比例性增加。

The 3 dB Rule and 5 dB Rule were evaluated for different sound pressure levels of noise. The noise utilized in this study was exposed to 30 mins broadband noise with four intensity level in 5 dB Rule (80, 85, 90, 95 dB) and 3 dB Rule(84, 87, 90, 93 dB). Audiograms were taken on 31 normal healthy men before and after 2 min exposure to noise (TTS2). Recovery from temporary threshold shift (TTS) was measured at various time (2, 20, 40, 60, 80 min) after a 30 min exposure to a broadband noise at 95dB. The results were as follows: With increasing sound pressured level noise, the hearing loss increased in the high frequency range. The hearing loss revealed a V-shaped cure at 4 kHz. The recovery of TTS was faster in the low and speech frequency range (0.5, 1, 2 kHz), whereas that in the high frequency range recovers much more slowly. The Reed-Muench method was used to calculate ED50 of noise exposure. The hearing loss equal to or more than 10 dB were defined as noise-induced TTS. ED50 was 83.81 dB SPL in 4kHz of 5 dB Rule. Comparing the prediction of hearing loss by using two rules (3 dB Rule and 5 dB Rule). In this study, the results tended to support the 3dB Rule. The Hearing loss increased proportionally to the noise energy.