Ergonomic Assessment of Work Posture and Evaluation of Hand-Arm Vibrations In Underground Mines

Abstract

The Indian mining industry is transforming highly mechanized operations by deploying Mobile Mining Equipment (MME) to increase production. The regular usage of MMEs comes up with a cost to the health of the operators in the form of increased risk for musculoskeletal disorders (MSDs). Several factors contribute to MSDs, including physical and psychosocial factors as well as organisational, interpersonal, and individual factors. These physical risk factors include vibrations, repetitive actions, heavy lifting or transporting, awkward postures, and intense exertions. The Directorate General of Mine Safety (DGMS), in its 11th Conference on Safety of Mines, has recommended conducting an ergonomic assessment of all the latest machines as per ISO standards. It is evident from the available literature that there is a significant research gap in this regard. Hence, there is an immediate need for ergonomic assessment of working postures and evaluation of hand-arm vibrations of miners working in Indian underground metal mines, along with the evaluation of acceptable workloads. This study was carried out in an underground metal mine in western India. Forty MMEs and their operators are used in underground mines for handling ore, and waste/overburden, such as Low Profile Dump Trucks (LPDTs) and Load haul Dumpers (LHDs), transporting personnel, explosive charging, scaling, breakdown rescue, and other multi-utility activities were involved in studying the workloads, working postures and the Hand Arm Vibration (HAV) exposure among the operators. Henceforth, the present study has five objectives. The study's first objective was to find the Aerobic Strain among MME operators due to the fact that the maximum aerobic capacity and relative aerobic strain could be employed as indicators to establish a balance between work and individuals. Unfortunately, information about the physiological demands of Mobile Mine equipment operators working in underground mines is nearly nonexistent. The present research aimed to determine the Mobile Mine equipment operators' maximum aerobic capacity and relative aerobic strain and assess their relationship with their age and Body Mass Index. Forty vioperators involved in transporting ore, overburden, mine personnel, explosives, repair material and etc., were examined. The maximum aerobic capacity was determined indirectly using the heart rate of the operators. The mean aerobic capacity of the operators was 38.75 mL/kg/min, and the lowest mean aerobic capacity was found in LHD operators, 37.98  3.93 mL/kg/min. The maximum aerobic capacity was negatively correlated with age and Body Mass Index. 11 out of 40 operators had relative aerobic strain exceeding 50% of the maximum aerobic capacity. The mean relative aerobic strain was 46.9  5.54, and the highest mean relative aerobic strain of 49.37  5.55 was found among LHD operators. The relative aerobic strain had a positive correlation with age and BMI. The study's second objective was to assess the work postures of the MME operators using the Rapid Upper Limb Assessment (RULA) method. The working posture of the operators was recorded with the aid of a digital camera. The frequently adapted posture by the operators was identified by analyzing the video graph and converted into a static image for the RULA. The RULA was performed using CREO-26 software by creating digital human models of the operators. The results from the study show that the MME operators frequently adapt postures that put them into the medium-risk category. Also, two operators adapted awkward postures with a RULA grand score of 7, representing the high-risk category. The statistical assessment carried out to find the association between awkward postures and MSDs of the upper extremities was significant, with a p-value of 0.06, implying that awkward posture was a significant factor in causing MSDs at the workplace. The third objective of the study was to evaluate the Hand-Arm Vibrations (HAVs) of LHD and LPDT operators based on different components of a job cycle. The study involved 12 LPDTs and eight LHDs. HTV readings were measured at the interface between the hand and the steering device using the SV 105B triaxial hand accelerometer connected to the SV106 human vibration analyzer adhering to the guidelines set by ISO 5349:200. The results from the study show that the z-axis was the dominant axis of viivibrations while performing hauling tasks. The empty hauling operations had the highest contribution towards total daily exposure A(8) in LPDTs. In the case of LHDs, high- vibration responses were recorded during the mucking operations with the x-axis as the dominant axis. The results also showed that six LPDTs and three LHDs were producing vibrations exceeding the stipulated Exposure Action Value (EAV) of 2.5m/s2. The fourth objective of the study was to assess the risk of the MSDs of the upper extremities of MME operators exposed to HAVs with a case-control approach. The study was carried out involving 80 male workers at the same mine. The research enrolled MME operators, office employees, supervisors, engineers, mechanical engineering, and logistics personnel. The case group consisted of 40 MME operators exposed to HTVs regularly, and the control group consisted of the remaining participants without any exposure to vibrations. Twenty-eight out of the 40 MMEs generated HTVs exceeding the stipulated daily vibration limits, putting 70% of the operators at increased risk for developing MSDs. The case group was found to have an elevated risk of exposure with an odds ratio (OR) of 7.56 (95% confidence interval (CI), 1.159, 49.39) and OR 12.80 (95% CI, 2.436, 67.285) times more likely than the control group to suffer discomfort in the left shoulder and left wrist, respectively, indicating an increased risk of exposure to HTV. Additionally, cases had elevated risk associated with exposure to tobacco, OR 9.35 (95% CI, 1.856, 47.129) compared to those who did not use tobacco. MSDs were more prevalent in the case group compared to the control group. The field investigations and the responses of MME operators to the questionnaires validated this observation.