In the United States, farm workers die from heat-related illness at an annual rate 20 times that of other workers. However, few studies have measured heat conditions at their actual work settings, and research is limited on how accurately regional weather reports reflect worksite temperatures.

The climate of outdoor worksites, such as farms, can differ from that of surrounding areas due to the sun’s energy, or solar radiation, wind speed, soil temperature, and other conditions. However, most recent studies on heat conditions affecting U.S. farm workers focus on regional weather reports. Can these reports accurately predict temperatures at specific farms? According to a NIOSH-funded study at Emory University published in the Journal of Occupational and Environmental MedicineExternal, they can.

Partnering with the Farmworker Association of Florida, these researchers explored the relationship between regional weather, or the macroclimate, and local farm weather, or the microclimate. Study participants included 105 farm workers from two Florida farming communities in Apopka and Immokalee. They were employed an average of 10 years, and their average age was 38.

For up to three days, study participants wore a small device, called an iButton, which attaches to clothing and monitors temperature and humidity in the wearer’s personal space. Researchers also collected local weather information from the Florida Automated Weather Network’s monitoring stations for the combined days of iButton wearing, for a total of 284 days during the summers of 2015 and 2016.

Researchers estimated farm temperatures based on the regional weather station data and compared these findings to the iButton readings. Study results showed that readings from the weather monitoring stations matched the conditions that research participants experienced, particularly when temperatures rose. For example, when the regional temperature was between 33.0°C and 40.0°C (91.4°F and 104°F), defined by the National Weather Service as heat illness risk levels of ‘‘extreme caution’’ and “danger,” the worksite often had similar numbers.

These findings are especially important for farm workers, who may not have devices available to measure worksite temperatures directly. Because weather-monitoring stations are widely available, researchers recommend that farming communities rely on the monitoring stations’ information as broadcasted on television and radio, as well as available on smartphones, to protect workers from heat-related illness. Additionally, NIOSH and the Occupational Safety and Health Administration have developed a Heat Safety Tool App that recommends prevention strategies based on local weather conditions.

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