The prediction of underground drilling noise

The current exposure limits of mineworkers to physical pollutants, under the Mine Health and Safety Act3 is 85 dB LAeq,8h, with a peak sound pressure level of 135 dB(A). However, the sound pressure level (SPL) of machines is generally determined according to the methods and procedures defined in SABS-ISO 3744 under free field conditions as defined in Appendix 3 of the same standard. While SPL and sound spectrum data obtained by this method are extremely useful for sound engineering purposes and direct comparison between different machines, the results can be considered only as an indication of the SPL level that any machine may produce during operation in an underground environment. In particular, the limitations of the free field method of SPL prediction of an expected SPL in the underground environment are as follows: