Monitoring and Assessment of Heat Stress and Heat Strain in Hot Arizona Mines

Abstract

Occupational heat stress is one of the main causes of health-related risks in the mining industry. Heat stress can cause heat strokes, heat exhaustion, hyperthermia and sometimes even death. Therefore, the importance of monitoring heat stress and using cooling technologies in a mine is critical to mitigating these occupational health risks. Heat stress is conventionally monitored using stress indices. The estimation of stress indices requires measuring dynamically changing parameters, which imposes a challenge to monitoring stress. Core body temperature (CBT) has proven to be a relevant proxy for heat stress. However, measuring CBT is an invasive technique that may not always be feasible. In the first part of this study, we identify two easily and non-invasively measurable physiological parameters: heart rate (BPM) and urine-specific gravity (USG). Further, we relate these parameters to CBT. We also investigate the dependence of these parameters on miners' physiological parameters, such as use of energy drinks and the body mass indices (BMI). Our findings show a strong correlation between CBT and heart rate (Pearson Correlation >0.4), rendering the latter as a useful tool to monitor heat stress. The intake of energy drinks shows causation to increase dehydration (p value=0.049). Furthermore, in the second part of this study, we investigate how to reduce the risk of heat stress in mine operators. In order to evaluate limiting factors, we examine the amount of heat absorbed by hardhats of different colors, where our findings are that white hardhats are best at absorbing minimal energy (15F less than black hardhats). Additionally, we study the performance of three commercial cooling vests and a combination set (i.e., evaporative cooling cap and sleeves) in reducing perceptual heat strain (23% of improvement in Physical Strain Alleviation wearing evaporative vest). We find that the overall perceived heat stress index of mine operators is considerably less with cooling devices.