Noise-induced hearing loss is the gradual loss of hearing that may occur on long or repeated exposure to intense noise. Such damage occurs at the organ of Corti in the inner ear and may become permanent. There is no known medical treatment to correct such hearing loss - emphasizing the importance of prevention. One of the first symptoms of noise-induced hearing loss is loss of hearing at the higher frequencies including 4000 Hz. The MSHA standard, or maximum allowable level, for noise exposure of miners is 90 dBA for 8 hours.
Most noise exposures at mining operations vary in level and frequency during a working shift.
MSHA measures personal noise exposure by means of a noise dosimeter which contains a microphone worn on the shoulder by the miner for a full shift. In addition to the use of a noise dosimeter, an MSHA inspector may make additional measurements with a sound level meter. The sound level meter allows the inspector to determine noise levels at specific locations at a given time. Such measurements are useful in locating excessively noisy areas, in determining which machines are the primary noise sources, and also in checking on there liability of personal noise dosimeter measurements. When an MSHA inspector places a noise dosimeter on a miner, it is important that the miner perform his work in the ordinary way, and that he not tamper with the device or create abnormal noises, either accidentally or intentionally.