Evaluation of operator whole-body vibration and shock exposure in a South African open cast mine

Abstract

This study quantifies whole-body vibration on a range of mine machinery typically used in a South African open cast mine. The ISO 2631-1 (1997) standard was used in the computation of weighted root mean square (WRMS) and vibration dose values (VDVs) whereas the ISO 2631-5 (2004) standard was used in the computation of daily static compressive stress (Sed) and R factor values. Two methods have been used to evaluate the whole-body vibration on a wide range of equipment used in an open cast mine. There are two main parameters for each of the standards. The ISO 2631-1 (1997) standard utilises the daily exposure A(8) and VDV, whereas the new ISO 2631-5 (2004) standard methodology uses the parameters Sed and R factor. ISO 2631-1 (1997) is poor in taking account of transient shocks. This led to the development of ISO 2631-5 (2004). Signals were therefore generated in the laboratory to further explore the parameters of the two standards. Vibration signals of more-or-less steady periodic processes can be approximated by superposition of sinusoids. To investigate the effect of shocks on the WBV response parameters used in the two standards, a series of investigations were conducted using very simplified simulations to capture the essential nature of various operational conditions, and qualitatively explain the trends in the response parameters. Pure sinusoidal data was first generated without shocks and investigated. Subsequently, sinusoidal signals with higher amplitudes were generated and investigated. Sinusoidal signals with increasing shock amplitude up to and exceeding the crest factor of 9 based on ISO 2631-1 (1997) were generated and analyzed. Finally, simulated data with different shock magnitude for five typical example cases were then generated and analyzed. The pure sinusoidal data was artificially generated using the signal generator at different amplitudes and frequencies, which are similar to field observed frequencies to enable numerical investigation of parameters to be carried out. A subset of the data was selected based on frequencies and amplitudes obtained on the field so as to have a representative data set on which investigations were carried out. The two parameters of the two standard methodologies were computed using simulated sinusoidal signal data. The trends in each of the parameters corresponding to each of the standards were monitored using various scenarios obtained by varying the signal parameters and compared against each other. There was approximate proportional correlation between the two parameters (VDV and Sed) with varying degrees of slope for each scenario. The Sed and VDV parameters are plotted on the x- and y-axes respectively. The graphs with slope greater than 1 corresponded to signals with low or no shock content; whereas the graphs with slope less than 1 corresponded to high shock content. The shock parameters (VDV and Sed) corresponding to the ISO 2631-1 (1997)and ISO 2631-5 (2004) standard methodologies were computed from field data and compared to see if the same trend obtained from the numerically obtained sinusoidal signals could be validated. It was found that the there was a gradual band correlation with slope less than 1 between the VDV and Sed parameters corresponding to signals of high shock content thereby validating the numerical findings. Since little or no extensive epidemiological studies have been carried out on the new methodology; it is recommended that more epidemiological studies be done to determine the exposure action and exposure limit values with respect to shocks in the Sed parameter for the new ISO 2631-5 (2004) standard methodology. It is advisable that caution is taking when using the new ISO 2631-5 (2004) standard methodology in evaluating whole-body vibration measurements until the limits are properly established. It is suggested that the new standard be used along with the established ISO 2631-1 (1997) standard methodology. Copyright