Grant Quiller

Project title: Heat stress, heat strain, and productivity in Washington State tree fruit harvesters

Degree: MS (Thesis) | Program: Occupational & Environmental Exposure Sciences (OEES) | Project type: Thesis/Dissertation
Completed in: 2016 | Faculty advisor: June T. Spector


Outdoor workers who perform heavy physical labor in hot conditions are at increased risk for developing occupational heat-related illness. Seasonal harvesting of certain tree fruits in Washington occurs during summer months. In addition to environmental heat exposure, harvesting involves internal heat generation from physical work. We sought to characterize heat stress and physiological effects of heat stress (heat strain) in outdoor tree fruit workers performing harvest activities. During the summer of 2015, 46 pear and apple harvesters participated in a cross-sectional study in Yakima Valley, Washington for one work shift each during warmer periods in August (n=34) and cooler periods in September (n=12). Heat stress and strain were characterized using American Conference of Governmental Hygienist (ACGIH) guidelines, which recommend thermal Action Limits and Threshold Limit Values based on several factors, including: environmental conditions, metabolic rate of task, and clothing ensembles. Heat exposure was measured near individual workers using hand-held Wet Bulb Globe Temperature (WBGT) monitors, metabolic rate was estimated using field observations and personal hip-mounted accelerometers, and research staff observed workers’ clothing. Heart rate and core body temperature were monitored over the course of the work shift using heart rate monitors and wireless ingestible core body temperature sensors. Surveys of the workers indicated that 24 (52%) had experienced symptoms of heat-related illness and only 13 (28%) received training on working in the heat. For the 34 participants who worked in pear harvest in August, 25 (74%) exceeded the ACGIH Action Limit (WBGT 25⁰ C), and 16 (47%) exceeded the Threshold Limit Value (WBGT 28⁰ C) for a moderate work task (300 Watts). Work during the month of September did not exceed the Action Limit, assuming a moderate work task. Using personal accelerometer data (n=39), 12 (31%) exceeded the Action Limit and four (10%) exceeded the Threshold Limit Value. The 12 participants exceeding the Action Limit, based on accelerometer data, underwent heat strain assessment using both ACGIH guidelines and the physiological strain index. Of these 12 participants, nine (75%) exceeded the recommended maximum heart rate (180-age), and five (42%) exceeded the recommended maximum internal core body temperature of 38.5°C. Under current environmental and work conditions, workers are being exposed to hazardous thermal environments. Effective approaches for reducing heat exposure and/or promoting biological adaptation to heat are needed to prevent heat-related illness in vulnerable working populations.