NOIRS 1997 Abstracts of the National Occupational Injury Research Symposium 1997. Washington, DC: National Institute for Occupational Safety and Health, 1997 Oct; :62
While the effects of either mining height or mine employment size on injury rates in underground coal mines have been examined separately, the present study attempts to examine the joint contribution of these two variables to the risk of injury to an underground miner. Using the mine- level employment and injury data reported to the Mine Safety and Health Administration (MSHA), mines were stratified by average coal seam height (<43 inches, 43-60 inches, and >60 inches) and by the average number of employees working at the mine (<20 employees, 20-49 employees, 50-99 employees and 100+ employees). The employment data show that as the number of employees increases, the proportion of hours worked in low seams decreases substantially. Additionally, miners injured in small low seam mines are, on average, younger and less experienced than miners injured in large high seam mines. Nonfatal and fatal injury rates were computed within each category of employment size and seam height for the major types of accidents (ground falls, powered haulage equipment, machinery, handling materials, slips and falls, hand tools). To reduce the confounding effects of mining method on injury rates, mines using longwall mining methods were identified and excluded from analysis. Results suggest that, regardless of the employment size, as mining height increases, miners are at increasingly higher risk of injury from accidents involving shuttle cars and falls of ground. Conversely, as mining height decreases, miners are at higher risk of injury from accidents involving roofbolting machines, load-haul-dump types of powered haulage equipment, personnel carriers, and powered haulage conveyors. On the other hand, regardless of the height of the coal seam, miners working in large underground mines have higher rates of injuries resulting from accidents involving handling materials and nonpowered hand tools, but lower rates of injury from accidents involving continuous mining machines and from fatal accidents involving falls of supported mine roof. As expected, injury rates for accidents involving a slip or fall increase as the seam height increases. However, the rate of injuries due to slips or falls also increases as the employment size increases. Finally, miners working at small mines in low or medium seams are at higher risk of being fatally injured by a fall of unsupported mine roof. These results suggest the importance of considering the working height of the mine as the well as the employment size of the mining operation when developing intervention strategies to reduce injury risk to underground coal miners. Results also identify the need to further explore how mining height contributes to the frequency and severity of injuries.