CIRS Blog about Rural California

Reducing the Risk: Heat and Farm Labor

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Despite the most stringent regulations in the U.S., agricultural workers in California continue to die from heat related illness, a preventable outcome, and are at higher risk than other workers exposed to hot environments. The search for effective and feasible solutions must involve diverse approaches appropriate for hired farm workers.

A current research project titled, “Reducing the risk of heat-related illness in western agricultural workers” brings together investigators from medicine, epidemiology, public health, physiology, rural sociology and community outreach and education. The group’s goal is to obtain novel data on internal body temperature as it relates to crop type and geography, external heat, and internal metabolic loading.

This long-term collaborative research project between the University of California Western Center for Agricultural Worker Health and Safety and the California Institute for Rural Studies will gather behavioral, physiological and environmental data from California agricultural workers and environments that will allow us to assess vulnerability to heat related illness, provide the methodology to test potential strategies in the fields, and disseminate results to stakeholders. The project employs innovative techniques for both understanding and evaluating potential solutions to reduce the risk of heat related illness in varied agricultural settings.

Previous research has not studied metabolic heat loading in California farmworkers or how such loading relates to illness. Existing studies have concentrated on environmental measurements, which do not allow complete risk analysis or the generation of meaningful solutions. As extreme heat events have increased for the past three decades and are projected to increase with global climate change, this research and anticipated outreach with culturally relevant solutions is both urgent and essential. Research findings and evaluated interventions will be translated into educational efforts in a manner that will have the highest impact on the most vulnerable farmworkers.

Over the course of the past summer, a team of students and investigators traveled throughout the Central Valley to take initial steps in gathering data for this project. They visited six geographically dispersed farms, one of which was visited twice, that included a wide variety of crops of varying heights from tomatoes, cantaloupe, watermelon and peppers to sunflowers and peaches. The team recruited 100 farmworkers for the study, monitoring up to five workers a day for three days at each farm.


Participants swallowed a thermometer sensor or “heat pill” to record their internal temperature and they wore a device to monitor their heart rate while they worked in the field at various jobs. Investigators measured personal ambient temperatures and humidity with the use of a “heat pen” that workers wore during their shift. Researchers conducted pre-shift and post-shift questionnaires with workers to examine current behaviors, workers’ knowledge of preventative measures, understanding of environmental conditions, personal health and work-related factors that increase vulnerability to heat-related illness. Two blood samples (about 5 drops of blood) were taken from each of the volunteers to determine changes in hydration by comparing pre-shift and post-shift blood electrolyte levels. Researchers also collected data on environmental conditions, including temperatures, by using stationary meteorological equipment. One of the pieces of equipment was placed near the workers to measure the environment in which they were working in and another was placed in a central location to measure temperatures of the entire surrounding area.

During the work shift, investigators observed participants every 15 minutes and noted the sun exposure, work rate, crop and crop height, the type of task that the workers performed, and the type of environment in which they were working. These direct field observations allow investigators to better understand the change or lack of change in physiological measurements, recorded by the “heat” pill.


The field research team included WCAHS team leaders jome Gutierrez and Rebeca Gallo; UC Davis undergraduates Javier Castro and Harsimran Singh; and graduate students Anna Jensen and Oscar Valenzuela. Study coordinator Diane Mitchell worked with study investigators Jim Jones, DVM, and Marc Schenker, MD, MPH, on site and in the lab, adjusting team deployment according to location changes and the weather.

This is the first stage of a multi-year project. Over the next several years, more information will be gathered to increase understanding of the physiological responses to environmental heat and physical exertion among farmworkers through the analyses of personal characteristics, monitors and sensors, and use the protocols developed to generate and validate risk models. Through farmworker focus groups and key informant interviews, the study will examine socio-cultural perspectives of heat related illness and identify both perceived barriers to adoption of prevention strategies and potential solutions that are acceptable to all parties. The team will continue to assess normal practices of farmworkers that impact risk of heat illness using epidemiological techniques.

It is the intention of this project to increase awareness of heat related illness as a credible personal risk to farmworkers in the western states. At the conclusion of this work, all research findings and evaluated interventions will be translated into educational materials in a manner that will have the highest impact on the most vulnerable farmworkers.


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Rebeca Gallo is a Community Health Program Representative Assistant at the Western Center for Health and Safety. She was one of the team leaders in the California Heat and Illness Prevention Study.
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