Predictions of health risks associated with the operation of load-haul-dump mining vehicles: Part 1—Analysis of whole-body vibration exposure using ISO 2631-1 and ISO-2631-5 standards

Abstract

Predicted health risks, associated with the operation of load-haul-dump (LHD) vehicles, based on ISO 2631-1 criteria are limited and have not yet been determined according to ISO 2631-5 criteria. Therefore, health risks predicted by ISO 2631-1 and 2631-5 criteria are reported and compared in this paper. Whole-body vibration (WBV) exposure was measured according to procedures established in ISO 2631-1. A tri-axial seat pad accelerometer was used to measure vibration exposure at the operator/seat interface. According to ISO 2631-1 criteria, calculated 8-h equivalent vibration dose values placed three of the seven LHD operators above the health guidance caution zone (HGCZ) boundaries and four LHD operators within the HGCZ. However, health risks predicted by the ISO 2631-5 criteria were always lower than the risks predicted by ISO 2631-1 criteria.

Relevance to industry

In 2004, ISO released a new standard for the evaluation of WBV, ISO-2631-5. The boundaries for probable health effects were established using the best guidance at the time; however, they have not been epidemiologically validated and very few studies have reported health risks based on ISO 2631-5 criteria. This study provides a comparison of predicted health risks based on ISO 2631-1 and ISO 2631-5 and provides data that could suggest the ISO 2631-5 boundaries for probable health effects may be set too high. Alternatively, the data presented in this paper suggests more dialogue is required to identify the appropriate application of ISO 2631-1 and 2631-5 given the different health risks predicted for a data set with high shock content.

Introduction

Operators of load-haul-dump (LHD) mining vehicles are exposed to whole-body vibration (WBV) and shocks during the course of their work (Eger et al., 2006a; Village et al., 1989). Exposure levels previously reported for LHD vehicle operators are limited, but they do suggest vibration frequencies are in a range that is harmful to human health (Eger et al., 2006a; Village et al., 1989). Most vibration frequencies are attenuated by the body; however, frequencies between 1 and 20 Hz can cause the body, including spinal column, pelvis, internal organs and soft tissues, to resonate (Kitazaki and Griffin, 1998; Thalheimer, 1996). Negative health outcomes include: lower-back pain, spinal degeneration, gastro-intestinal track problems, sleep problems, headaches, neck problems, and autonomic nervous system dysfunction (Scutter et al., 1997; Seidel, 1993, Seidel, 2005; Thalheimer, 1996). Although epidemiological studies are limited, several researchers have reported elevated rates of low back injury and neck injury amongst LHD operators when compared to other underground mine workers who do not operate mobile equipment (Eger et al., 2006a; Village et al., 1989). Therefore, vibration exposure levels are likely contributing to the development of back and neck injuries amongst LHD operators.

In order to prevent negative health outcomes associated with WBV exposure, a risk assessment, based on published standards, can be conducted. The most widely accepted standard for measurement and evaluation of human exposure to WBV and subsequent prediction of health risks is the International Organization of Standards (1997) report entitled ISO 2631-1: Mechanical vibration and shock—Evaluation of human exposure to whole-body vibration, Part 1—General requirements. This standard provides guidance on the quantification of WBV in relation to human health and comfort, the probability of vibration perception, and incidence of motion sickness. In 2004 the International Organization for Standardization introduced a new standard for the evaluation of human exposure to WBV that contains multiple shocks, called ISO 2631-5: Mechanical vibration and shock—Evaluation of human exposure to whole-body vibration, Part 5—Method for evaluation of vibration containing multiple shocks. The foundation for the new standard was laid by a series of research reports commissioned by the United States Army Aeromedical Research Laboratory between 1991 and 1997 (Cameron et al., 1996, Cameron et al., 1998; Morrison et al., 1998; Roddan et al., 1995; Village et al., 1995a, Village et al., 1995b). The new ISO standard was established to quantify health risks specifically to the lumbar spine and the vertebral endplates as a result of WBV exposures containing multiple shocks. This is important as driving machinery over rough terrain, such as a LHD vehicle in an underground mining environment, is likely to expose workers to vibration with repeated high shock components.

Previous evaluations of WBV exposure associated with the operation of LHD vehicles have not included an ISO 2631-5 analysis. The 1989 study conducted by Village and colleagues was completed over 15 years ago under procedures established in ISO 2631/1 (1985). As a result, the weighting factors used in the calculation of the frequency-weighted acceleration values were different than the weighting factors used in the current 1997 ISO 2631-1 standard while the ISO 2631-5 standard did not exist at that time. The 2006(a) study conducted by Eger and colleagues only examined three LHD vehicles (as part of a larger evaluation of 15 different types of mining vehicles) and comments on health risks were based on ISO 2631-1 health guidance caution zone (HGCZ) limits. The recent study by Salmoni and colleagues (2006) was more comprehensive; however, health risks based on the ISO 2631-5 standard were not reported.

Given the short period of time since the conception of ISO 2631-5, very few studies have been reported in peer-reviewed publications or published conference proceedings. In 2005, Alem discussed the suitability of ISO 2631-5 for the evaluation of repeated shocks during operation of different army vehicles. He compared health risks predicted by frequency-weighted r.m.s. acceleration values (ISO 2631-1), vibration dose values (VDV) (ISO 2631-1), and daily equivalent static compression dose (S_ed) values (ISO 2631-5). He selected 40 ride profiles with high shock content for analysis from a United States army database and found a high probability of risk to the spinal system was indicated by the calculated S_ed value. Health risks predicted by the ISO 2631-1 variable, VDV, were lower than the health risks predicted by the S_ed variable from ISO 2631-5. However, Johanning et al. (2006) and Cooperrider and Gordon (2006) reported low health risks for locomotive operators based on ISO 2631-5 criteria and higher health risks based on an ISO 2631-1 analysis. Therefore, given the limited number of published reports that compared ISO 2631-1 and ISO 2631-5 standards and the differing outcomes in these reports, additional research is warranted.

The present study had three objectives. First, given the limited information regarding the characteristics of WBV exposure associated with the operation of LHD vehicles, a description of vibration measured at the operator/seat interface is reported. Second, predicted health risks associated with the operation of a LHD vehicle, based on criteria established in ISO 2631-1 and ISO 2631-5, are reported. Third, predicted health risks suggested by ISO 2631-1 variables (VDV_total; A(8)) and ISO 2631-5 variables (S_ed; R factor) are compared in an effort to determine if the two approaches predict similar health risks.