M. Hegarty-Craver, H.J. Walls
RTI International,
United States
Keywords: wearables, heat strain, protective garments, personal protective equipment
Summary:
Background: Heat-related injuries are common among individuals who need to wear protective garments to reduce their risk of exposure to environmental threats including soot and smoke. Wearing protective garments in warm and humid environments (e.g., such as when fighting wildfires) further increases risks for developing heat-related injuries. Because protective garments are designed to be impervious, both heat transfer from the body to the environment and cooling through sweating are disrupted. Occupational heat strain can significantly impact productivity, increase risk of injury, and have long-lasting health consequences. Because of these risks, new protective garments should be evaluated based on the level of protection they offer and the thermal burden (i.e., the additional strain that is placed on the human body when exposed to heat) they induce. Our team developed a protocol to measure the thermal burden of different protective garments and piloted this protocol with 4 experimental garments worn by a human test participant (TP). Methods: The TP performed a 30-minute exercise routine while wearing a Garmin smartwatch (physical activity and heart rate [HR]), Polar H10 heart rate monitor (HR), and Calera CORE sensor (core body temperature [CBT] and skin temperature) in a controlled wind tunnel environment. Six tests were performed on different days to assess 4 research garments, traditional firefighter turnout gear (Positive Control), and traditional athletic wear (Negative Control). The temperature in the wind tunnel was maintained between 78.7°F and 80.1°F and the humidity was maintained between 47.6% and 54.5%; the wind speed was set to 3 mph. Resting measurements of HR and CBT were taken for 10 minutes before entering the wind tunnel. Recovery measurements of HR were taken for 3 minutes after exiting the wind tunnel. Results & Discussion: Resting measurements of HR and CBT were stable on all test days. Indicators of exertion increased over the 30-minute wind tunnel motion routine, but individual metrics of HR and CBT followed different trajectories. HR and CBT rose the fastest for Experimental Garment #1 and the Positive Control and remained relatively unchanged for the first 20 minutes of exercise for Experimental Garment #3 and the Negative Control. HR recovered the quickest for Experimental Garment #3 and the Negative Control and slowest for the Positive Control. While the participant tried to maintain a similar level of effort across tests, the smartwatch indicators of physical activity suggest that effort level was greatest during the first test (Experimental Garment #1) and lowest during the fifth test (Positive Control). To account for these differences, we standardized the Physiological Strain Index (which uses measures of HR, CBT, and skin temperature) by the average total energy. These standardized values indicated that thermal burden was highest for the Positive Control and lowest for the Negative Control and stratified the experimental garments. Next steps include expanding our TP pool and assessing repeatability. Also, because we used commercially available wearables, we are investigating how our measurement protocol could be used in practice to monitor thermal burden continuously to prevent heat-related injuries.