Comparison of Heat Stress Risk Within Crops Rows to Perimeter in Sweet Corn and Tobacco Fields

Abstract

Introduction- Agricultural work is one of the highest risk US occupations for heat-related illness (HRIs). Farm and crop workers, who commonly perform strenuous labor under direct sunlight, were 35 times more likely to die from HRIs than workers in other industries. Some tall-growing crops can block the cooling effects of wind or contribute to environmental humidity, yet few studies have included measurements of farmworker microclimates (environments directly surrounding workers). The purpose of this study was to assess the differences in heat stress within crops rows compared to the field perimeter. Methods- In the summer of 2023, two QUESTemp°34 heat stress monitors were set up daily from 8AM to 5PM in crops fields in Bertie and Columbus counties, in the warmest region of North Carolina. Two crops were selected, sweet corn and tobacco, and measurements were collected over 27 days in June and 27 days in July and August, respectively. The monitors measured wet bulb globe temperature (WBGT); which includes temperature, humidity, wind speed, sun angle and cloud cover, and is the preferred occupational heat stress measure. The hourly WBGT averages were compared to the American Conference of Governmental Industrial Hygienists’ Threshold Limit Values (TLVs®). The TLVs provide a recommendation on permissible WBGTs to work in based on breaks and workload. Data analysis (SPSS, v28.0) included independent sample t-tests. Results- There were significantly higher WBGT measurements inside of the row compared to the field perimeter for peak (11AM-2PM) and afternoon (2PM-5PM) times in tobacco. The morning (8AM-11AM) and peak humidity in both tobacco and corn was also significantly higher within the crop rows. With corn, the field perimeter was above recommended TLVs 38 hours (16.9% of total hours) and the center of the field was over the TLVs 53 hours (23.6% of total hours). With tobacco, the field perimeter was above recommended TLVs 141 hours (73.4% of total hours), and the center of the field was over the TLVs 167 hours (87.0% of total hours). Conclusion- In the summer of 2023, farmworkers in the study area were potentially at an increased risk for HRIs due to warm and humid microclimates within corn and tobacco crop rows. As environmental heat stress is increasing due to climate change, the greater risk of working inside tall crop rows should be considered in worker education and heat stress plans, such as more frequent breaks at midday and in the afternoon.