Mining Project: Predicting the Impact of Heat Strain on Cognitive Functions in Miners
To establish whether easily measured physiologic (i.e. heart rate, internal body temperature) and environmental parameters (i.e. air temperature, relative humidity, and wet bulb globe temperature) can effectively predict heat strain-related cognitive impairment among miners.
Heat stress refers to the total heat load placed on the body, from external environmental sources and from physical exertion, whereas heat strain refers to the physical strain the body experiences as a result of heat stress. Heat strain can lead to serious injury. A possible mechanism by which this occurs is through heat-related cognitive dysfunction. However, studies on heat-related cognitive function have not been conducted in U.S. miners. Studies are needed to evaluate the effects of heat exposure on miners’ cognitive performance, assess which mining job tasks are at highest risk of impact from heat exposure, assess which miners are at highest risk of heat strain, and investigate the effectiveness of the designed solutions.
Despite the use of various heat indices at mines throughout the world, a standard heat index has not been identified in the mining industry. Furthermore, most indices have been evaluated primarily as predictors of elevated body temperatures that can lead to heat illness. Each index has limitations, and indices do not account for individual variability in heat tolerance that is partly a result of personal risk factors such as previous heat illness, age, lack of acclimatization, pregnancy, obesity, alcohol use, certain medications, and other health conditions. Heat exposure may precipitate other adverse consequences other than heat illness. For example, heat strain has been associated with cognitive impairment and increased injury risk. Thus, it is reasonable to hypothesize that heat exposure might contribute to injuries in the mining industry. Determining predictors of heat-related cognitive impairment could have widespread benefit in mining.
To address these issues, this project has three research aims:
- Determine if an increase in heat stress from environmental parameters such as temperature and humidity and the subsequent increase in heat strain (heart rate and body temperature) correlates with decreased cognitive performance.
- Assess the extent to which identification and assessment of personal risk factors can improve the prediction of cognitive impairment.
- Develop recommendations to improve the detection, mitigate the risk, and identify workers with increased susceptibility to heat-related cognitive impairment among miners.
To accomplish these aims, Mining Program researchers will investigate the relationship between miners’ cognitive performance and physiologic and environmental measurements of heat strain using both laboratory and field research. Questionnaires and interviews will be used to collect data on personal risk factors, metabolic work load, and hydration status. Heart rate and temperature monitors will measure physiologic factors. Data on body mass index, body fat percentage, hydration level, fatigue, and overall fitness will be collected. Various cognitive tests will be employed to evaluate aspects of cognitive function, including sustained attention, reaction time, and working memory.
Laboratory research will consist of evaluating cognitive changes among subjects performing aerobic and resistance exercises in a chamber in which temperature and relative humidity conditions can be precisely controlled. Mixed effects modelling methods will be used to evaluate associations between cognitive test results, physiologic and environmental measurements, and personal risk factors for both field and laboratory data. The predictive power of specific combinations of physiologic and environmental measurements and risk factors on miner cognitive performance will be assessed.
Field research will entail measuring participants’ continuous heart rates and body temperatures as they perform their job tasks in hot environments. Environmental conditions (e.g. dry bulb temperature and humidity) in participants’ work areas will also be measured. Cognitive testing will be administered two times per shift to evaluate changes from baseline.
This project research is expected to have the following potential impacts:
- provide a better understanding of the most important personal factors to consider in predicting which miners are at highest risk of adverse outcomes;
- provide information that can be useful in influencing health and safety policies and education programs on heat stress; and
- develop a tool for use at individual worksites to provide individual miners with specific information relating to the risk of cognitive deficits that could lead to adverse outcomes.
This project constitutes extensive follow-on research to the one-year pilot project, “Predicting Heat Strain in Underground Metal and Nonmetal Miners,” which helped to shape the research methodology and aims. Ultimately, findings from this research will increase knowledge of heat strain in U.S. mining and provide information on the extent to which heat strain affects cognitive performance. The study will contribute scientific evidence that the mining industry and other industries whose workers experience heat exposure can use to develop guidelines and policies to mitigate the risk of heat strain and its complications.
Heat Stress: A Series of Fact Sheets for Promoting Safe Work in Hot Mining Settings (six downloadable fact sheets)
A Study of Heat Stress Exposures and Interventions for Mine Rescue Workers (conference paper)
Patterns of Heat Strain Among a Sample of US Underground Miners (peer-reviewed journal article)
Heat Stress (NIOSH topic page)