Farmworker-Relevant Heat Exposure in Different Crop and Shade Conditions

ABSTRACT

Objectives

Agricultural workers are at risk of heat-related illness, which is preventable. Few field studies have compared farmworker-relevant heat exposure in different conditions. We examined heat exposure over time in different potential shade and work locations to inform future occupational heat prevention approaches.

Methods

We assessed heat exposure in Eastern Washington State (WA) cherry and grape fields in August 2022. QUESTemp° monitors recorded Wet Bulb Globe Temperature (WBGT) and Black Globe Temperature (BGT) every 10 min from approximately 07:00–14:00 for three days in the center of crop rows (mid-row), under portable shade structures (shade), and in open field (open) locations. Linear mixed effects regression (LMER) models compared WBGT and BGT among field locations. Hourly time-weighted average WBGT and comparisons with occupational exposure limits (OELs) were computed for different hypothetical work-rest cycles during the hottest sampling hours, assuming different worker effort levels, rest locations (mid-row versus shade), and acclimatization statuses.

Results

Across all crops and locations during the study period, the mean/SD air temperature was 31°C (88°F)/3.9°C (6.9°F), with a maximum temperature of 39°C (102°F) and a mean/SD relative humidity of 30%/9.6%. LMER models suggested no significant difference in mid-row versus open WBGT but significantly lower WBGT in shade versus open locations for both cherries (main effect −5.14: 95% confidence interval [CI] −6.97,−3.32) and grapes (−6.20: 95%CI −7.73,−4.67), though this difference diminished over the course of the day. BGT was significantly higher in the mid-row than the shade (cherries main effect 14.33: 95%CI 9.52,19.13 and grapes 17.10: 95%CI 13.44,20.75). During the hottest sampling hour, the exceedances of OELs were reduced with assumptions of increased shaded break lengths, reduced effort level, and acclimatization.

Conclusions

Shade canopies, but not the crops studied, provided significant reductions in heat exposure. We observed increased protection from heat assuming longer shaded breaks and reduced effort levels. Results highlight the need for additional field research on the effectiveness, feasibility, and acceptability of different shade types and work-rest cycles to guide employer optimization of best practices for worker protections, including acclimatization before high heat, sufficient shaded rest time, reduced effort levels as the day warms, and avoiding work in peak heat.

KEYWORDS:

• Heat stress
• field study
• shade
• farmworker

Acknowledgments

The authors wish to thank Washington State University’s Maurisio Garcia, Josh Goicoechea, and Dr Lav Khot for their assistance with coordinating access to the Irrigated Agriculture Research and Extension Center, Marc Beaudreau and the University of Washington (UW) Field Research and Consultation Group (FRCG) and Miyoko Sasakura and Tyler Young at the Washington State Department of Labor and Industries’ Division of Occupational Safety & Health for their assistance with QUESTemp° monitors, and Dr Edward Kasner, Pablo Palmández, and the UW Pacific Northwest Agricultural Safety and Health (PNASH) Center for their assistance and support.

Disclosure statement

The authors report no financial or non-financial conflicts of interest.

Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/1059924X.2024.2365647

Additional information

Funding

This research was funded by Centers for Disease Control and Prevention/National Institute for Occupational Safety and Health [Grant numbers 5U54OH007544], the National Institute of the Environmental Health Sciences (NIEHS) Biostatistics, Epidemiology, and Bioinformatics Training in Environmental Health (BEBTEH) from the NIH/NIEHS, grant number T32ES015459 and the Washington State Department of Labor and Industries. This content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health, the Centers for Disease Control and Prevention, or the Washington State Department of Labor and Industries.