Measuring mining safety with injury statistics: Lost workdays as indicators of risk

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Abstract

Problem

Mining in the United States remains one of the most hazardous industries, despite significant reductions in fatal injury rates over the last century. Coal mine fatality rates, for example, have dropped almost a thousand-fold since their peak in 1908. While incidence rates are very important indicators, lost worktime measures offer an alternative metric for evaluating job safety and health performance. The first objective of this study examined the distributions and summary statistics of all injuries reported to the Mine Safety and Health Administration from 1983 through 2004. Over the period studied (1983–2004), there were 31,515,368 lost workdays associated with mining injuries, for an equivalent of 5,700 person-years lost annually. The second objective addressed the problem of comparing safety program performance in mines for situations where denominator data were lacking. By examining the consequences of injuries, comparisons can be made between disparate operations without the need for denominators. Total risk in the form of lost workday sums can help to distinguish between lower- and higher-risk operations or time periods.

Method

Our method was to use a beta distribution to model the losses and to compare underground coal mining to underground metal/nonmetal mining from 2000 to 2004.

Results

Our results showed the probability of an injury having 10 or more lost workdays was 0.52 for coal mine cases versus 0.35 for metal/nonmetal mine cases. In addition, a comparison of injuries involving continuous mining machines over 2001–2002 versus 2003–2004 showed that the ratio of average losses in the later period to those in the earlier period was approximately 1.08, suggesting increasing risks for such operations.

Discussion

This denominator-free safety measure will help the mining industry more effectively identify higher-risk operations and more realistically evaluate their safety improvement programs.

Impact on Industry

Attention to a variety of metrics concerning the performance of a job safety and health program will enhance industry's ability to manage these programs and reduce risk.

Section snippets

Problem

Researchers in occupational safety and health fields who use surveillance data rely on a small number of risk measurement methods for evaluating the performance of preventive programs. The raw numbers of reported injuries and illnesses plotted over time provide the first indications of higher-than-average risk problems, or lower-than-average risk success stories. Calculating incidence rates when denominator data (i.e., number of workers exposed) are available is a more standardized measure,

Literature review

The use of statistics in job safety and health has a long history, and in particular, MSHA's use of so-called statutory days has its origin in a 1920 Bureau of Labor Statistics Bulletin No. 276, Standardization of Industrial Accident Statistics (U.S. Bureau of Labor Statistics, 1920). The authors felt there was a need for a uniform system for assigning lost work time to disabling injuries and deaths. The results included, for example, a statutory charge of 6,000 lost workdays for a fatal injury

Methods

The following background on MSHA reporting requirements and practices are important for understanding this study. Underground and surface mining are part of the extraction industries in the United States. The general categories of commodities mined are coal, metal, nonmetal, stone, and sand and gravel. The accident data for this study were collected by MSHA, part of the Department of Labor. MSHA has collected mine accident data for many years, providing public access to data from 1983 forward

Summary of lost workday trends

For the period 1983 through 2004, MSHA received 321,011 case reports of nonfatal injuries with lost workdays. A total of 2,215 fatal injuries was also reported in this period. The sum of lost workdays, statutory days lost, and days of restricted work activity for all of these cases was 31,515,368 over 22 years, or the equivalent of more than 5,700 person-years lost annually.

For consistency with MSHA's convention, and for comparison with its published data, the overall loss data were separated

Discussion

It's well known that surveillance data of occupational injuries and illnesses for U.S. industries in general have significant limitations. Researchers are frequently faced with drawing conclusions from data that has been collected primarily for purposes other than research, including regulatory, administrative, and legal requirements. Public health practitioners are constantly faced with decisions that require prioritizing activities and interventions in the face of incomplete and

Data and methodology limitations

The limitations of the MSHA data deserve some discussion. Specifically, the use of statutory days as a measure of injury severity raises several questions. Are the assignments of statutory days charged based on scientific methodology? Does MSHA arbitrarily assign such values to each applicable case? In practice, the tables and charts that explain the assignment of lost workday equivalents to specific impairments of body parts are based on medical histories and the opinions of medical

Summary

This study was motivated by the search for a wider set of indicators for the effectiveness of safety program performance in mines. MSHA maintains a very thorough and detailed database of job injuries and illnesses reported by mining companies and contractors. However, denominators in the form of hours worked are not sufficiently detailed by category to allow traditional estimates of risk to be calculated for a variety of variables. Without denominators and the incidence rate calculations they

Impact on Industry

As in the use of balanced score cards in business management (Kaplan & Norton, 1996), a wider variety of measures can help to ensure that programs are performing as intended. In mining, as well as in other industries, job injuries are not only lagging indicators, but are often too infrequent to be used as day-to-day indices of program performance. While lost time measures do not provide more frequent indications, they can help the mining industry improve important aspects of their safety

Patrick J. Coleman, PhD, CMSP, is a research epidemiologist who studied occupational safety and health in Wisconsin companies from 1972–79, conducting worker hazard surveys to understand how workers perceived and controlled the hazards they faced on their jobs. In 1979 he became chief of surveillance in NIOSH's Division of Safety Research, conducting studies of job injuries and their causes until 1984. Until 1999 he worked as a statistician and epidemiologist in CDC's Hepatitis Branch, applying

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    Consistently actual mining operations was found to be the most dangerous activities, as job titles, causes of accidents, accident locations and time of accident associated with high consequence accidents such as fatalities were mostly related to mining operations activities like drilling, blasting, loading and hauling. This observation seems intuitively obvious as it agrees with previous observations (Coleman & Kerkering, 2007; Muzaffar et al., 2013; Ruff et al., 2011). The presence of mobile mining equipment has long been identified as a priority area in both surface and underground mines and this was rightly observed in this study.

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Patrick J. Coleman, PhD, CMSP, is a research epidemiologist who studied occupational safety and health in Wisconsin companies from 1972–79, conducting worker hazard surveys to understand how workers perceived and controlled the hazards they faced on their jobs. In 1979 he became chief of surveillance in NIOSH's Division of Safety Research, conducting studies of job injuries and their causes until 1984. Until 1999 he worked as a statistician and epidemiologist in CDC's Hepatitis Branch, applying statistical and epi models to national hepatitis data. Since then, he rejoined NIOSH at the Spokane Research Lab, and has worked on research into U.S. mining job safety and health, applying epi methods to the monitoring and surveillance of mining injuries and illnesses.

John C. Kerkering, MA, is a mathematician with NIOSH at the Spokane Research Laboratory. He has worked on improving safety in mining since 1975, first with the US Bureau of Mines, and then with NIOSH. His principle interest has been in employing formal safety techniques, such as fault and event tree analysis, to improving mine safety.

The findings and conclusions in this report are those of the author(s) and do not necessarily represent the views of the Centers for Disease Control and Prevention/the National Institute for Occupational Safety and Health.

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