Comparison of noise reduction of earplugs between fit test and coal mine work and observed variability of real-time noise reduction in coal mine work.

BACKGROUND: The coal mining industry relies heavily on a hearing protector (HP) for noise protection. Researchers suggested that individual HP fit tests be conducted to estimate the noise attenuation.

OBJECTIVE: This study examined whether individual fit tests accurately predicted workers' ear plug noise protection while working and whether the real-time noise reduction (NR) remained constant in mining work while an ear plug was worn.

METHODS: A total of 11 subjects from 3 coal mines each was fit tested using the microphone-in-real-ear (MIRE) technique on their E-A-Rtrademark earplugs in a typical mine office. The same fit tested miners each wore the same type of earplugs in his usual manner doing his normal work. The minute-by-minute real-time NRwork values were determined continuously during full shifts of work.

RESULTS AND CONCLUSIONS: Results showed there was a modest prediction relationship (R2 = 0.53) between NRfit and NRwork. NRwork values of each miner's earplug fluctuated over 20 dBA while the earplug was worn. However, each was still able to achieve an average NRwork of more than 10 dBA, indicating the earplug was somewhat effective in reducing noise, if worn. Refitting was an important cause of the low NRwork values. Low-frequency noise sources might be also important causes.