Numerous studies have shown the effects of working in extreme heat.^{4,5,6,7,8,9,23} A study of core body temperature (Tc) over three Florida summers found that on an average workday, 49% of participants exceeded core temperature over 100.4°F (Tc38°C) and 10% exceeded 101.3°F (Tc38.5 °C), thresholds established by NIOSH.17,23 In a study of 192 farmworkers working in the Florida summer heat, over half (53%) started their workday dehydrated (urine specific gravity USG<=1.02); 81% were dehydrated after a day of work; and one third had acute kidney injury (AKI) at least once during the three summer workdays they were monitored. The odds of AKI increased 47% for each heat index increase of five degrees.⁴ Heat damage may be cumulative over time. A study of fernery workers working in the heat found the prevalence of acute kidney injury increased from 21 to 43% over three years.²⁴

Moyce et al., studying agricultural workers in California, found AKI was associated with accelerated physical workload and core temperature elevations.⁶ Mac et al. found higher heat index and higher physical activity level were linked to more physiological strain, indicated by elevated heart rates and core body temperatures.⁸

Work setting also plays a role in physical activity levels. Mix et al. found fernery workers, who are usually paid for piecework or by volume, had more sustained physical activity than other agricultural workers and did not reduce the intensity of physical activity under dangerously hot conditions.5 Similarly, piece-rate work has been associated with increased adjusted odds of AKI (3.02, 95% CI1.44–6.34) in California agricultural workers⁶ and in Florida farmworkers.²⁴

Adding to the heat risks of farmworkers are other health conditions, prevalent among the general population as well as farmworkers. One study with Florida farmworkers found the prevalence of overweight or obesity, elevated blood pressure, and prediabetes to be high (83%, 70%, 60%, respectively), and that these conditions were compounded by limited access to health care.²⁵

Many farmworkers may not be able to cool down significantly after working in the heat. A North Carolina study found the heat indexes in farmworker housing frequently were high.²⁶ The high cost of electricity for air conditioning (when available) and fans in the high heat and humidity limits their use.

A scoping review of 92 articles identified multiple risk factors and protective factors for heat-related health harm.⁹ The risk factors included gender, dehydration, heat strain, wearing inappropriate clothing, workload, piece-rate payment, and hot environmental conditions. Drinking water and electrolyte drinks and taking breaks in shaded or air-conditioned areas were identified as protective and preventive factors.

Few studies have looked at workplace factors that could mitigate some of the physiological strain and heat risks. A small study (n=37) in Washington State found that after training on HRI, some workers reduced the intensity of their physical work and the associated physiological strain.²⁷ A pilot study by Chicas et al. found workers wearing cooling bandanas were less likely to exceed core temperature of Tc38°C.²⁸ Although wearing bandanas is an individual, not workplace, preventive action, it could be incorporated into a workplace protection strategy. This study examined working conditions, alignment of NIOSH-recommendations for breaks, and prevalence of dehydration and HRI in summer and winter in Central Florida.

Emory University Nell Hodson Woodruff School of Nursing researchers worked with the Farmworker Association of Florida (FWAF) to study heat exposure and its impact on agricultural workers in Florida. Emory University Institutional Review Board approved the study (IRB00112681), which was funded by NIOSH.

Farmworker Association of Florida is a grassroots community-based organization with about 10,000 farmworker members and strong ties in the farmworker community. Most of the staff and the board of directors have been farmworkers or are from farmworker families. Building on the trust and relationships with the farmworkers, community health workers from FWAF recruited a convenience sample of agricultural workers who met the inclusion criteria of being Hispanic, currently working in agriculture, and being ages 18–49, from two FWAF locations in Central Florida in January 2020. Those with Type I diabetes, pregnancy, hypertension treatment, a history of renal disease, or less than a month of working in agriculture were excluded. Data collection was conducted in two FWAF field offices by trained interviewers using the participants’ primary language, which was always Spanish. The FWAF offices are in areas where the majority of many farmworkers live or work. This proximity as well as the farmworkers’ familiarity with FWAF facilitated participation. After the morning measurements, workers dispersed to their worksites and returned for post-workday measures and interviews. The worksites were not selected by the researchers; the farm-workers went to their usual worksite or where work was available that day, primarily nurseries and ferneries.

Interviewers queried participants in January 2020 and 2021 and once each of three summers (August 2020, July 2021, and August 2022), for a total of 199 winter and 260 summer workdays. Data collection days were based on the season (summer or winter). At the start of the project, 115 people were enrolled. Over the course of the study, some participants did not have agricultural work on the data collection periods; these visits were excluded from the current analysis (n=37 non-agricultural days from 21 participants). Study retention has been reported elsewhere.²⁹

The first visit data collection, conducted on a non-workday, recorded demographics, work history, and typical workplace conditions. After a workday in each of the five data collection periods, the number and duration of rest breaks and lunch were queried, as were types and quantities of beverages consumed. Heat-related illness symptoms experienced on that workday were queried (heavy sweating, headache, fainting, confusion, dizziness, cramping, nausea/vomiting). The presence of any fainting, confusion, dizziness, cramping, or nausea/vomiting was considered “serious HRI.” Urine samples were analyzed before and after a work shift with an ATAGO meter (PAL-10S digital refractometer, Bellevue, Washington, https://atagousa.corecommerce.com) that measured urine-specific gravity (USG) with an accuracy of ±0.001 and a resolution of 0.0001. As a quality-control measure, distilled water was measured each morning before the start of data collection. Dehydration was defined as USG greater than or equal to 1.02.

The Florida Automated Weather Network (FAWN) monitoring stations, managed by the State of Florida to aid agricultural management, located in the study areas near the worksites collect weather data every 15 minutes throughout the year. The Lu-Romps extended heat index (HI) algorithm based on data-collection day FAWN ambient-temperature measures and relative humidity was used to calculate the maximum, minimum, and median heat index over the workday, individualized for each worker’s location and work hours.³⁰ Hours spent at HI greater than or equal to 90°F and greater than or equal to 100°F were calculated for everyone.

Descriptive statistics such as medians and percentages, season-adjusted and other simple regressions were calculated using either the mixed or glimmix procedures in SAS v9.4 and R package lqmm v1.5.8, adjusting for random effects of repeat measures on the same individual and for household/family connections.³¹

Observed over three summers, each of these Florida farmworkers was working at least part of their day in extreme environmental heat and humidity that requires extreme caution. However, despite this, recommended risk-reduction strategies were not part of their workday. The workers had only two daily breaks, on average, significantly fewer than NIOSH recommends.^3,17 This is also less than required in California and Oregon. Workers drank about a third of the recommended amount of beverage consumption. The agricultural industry and other industries with workers in the heat have lobbied against the enactment of federal and state heat-protection standards, countering that heat-protection recommendations are already being followed in the workplace and that regulations would only burden businesses unnecessarily.^22,32,33 Our findings do not support their contention that recommendations are being followed voluntarily.

Workers endured intense heat for several hours in the summer, with excessive exposure to heat risks. They worked 7.8 hours (median), with some laboring 12 hours, with a median heat index of 95°F and a heat index high of 131°F, with few breaks. Although the summer heat exposures were extensive, workers did not have more breaks in the summer than in the winter. The National Institute for Occupational Safety and Health recommends workers have one break at least every two hours in the heat, 15-minute rest breaks for every hour of moderate work in heat caution temperatures (heat index greater than or equal to 90 degrees F) and 30-minute rest breaks for every 30 minutes of work in danger heat (heat index greater than or equal to 100 degrees F).^3,17 None of the workers had the number of breaks recommended by NIOSH. Only 28% had three or more breaks including lunch, which might approximate one break every two hours in a full workday. Notably, the number of rest breaks increased very little for workers working in extreme-caution (greater than or equal to 90 degrees F) and danger-zone (greater than or equal to 100 degrees F) heat indices. Furthermore, the timing of the few breaks workers had is unknown; they may not have been during the hottest periods. This pattern of few breaks illustrates the limitation of NIOSH recommendations: the guidance is not followed voluntarily in the workplace. The few rest breaks were likely insufficient for workers to counter the high temperature exposures they experienced.

Rising temperatures and brutal heat expose workers to preventable harm. The National Institute for Occupational Safety and Health recommends workers have training on preventing HRI, in addition to more rest breaks, increased hydration throughout the workday, and additional precautions in high heat-index conditions. Yet only 31% of the workers studied reported ever having had any training on preventing HRI; the quality of the training is unknown. Training on HRI was often mixed with pesticide training, which can dilute both topics and add confusion regarding which symptoms are associated with heat or pesticides. The majority who were trained were trained by supervisors or employers. The training on HRI may have been insufficient for workers to understand what symptoms to watch for and may not have provided enough feasible strategies to counter the heat. Regardless of training, workers have little ability to control when they can take breaks unless supported by crew leaders and employers. Crew leaders and employers are not required to have training in preventing HRI.

Dehydration reduces the body’s ability to release excess heat, contributes to HRI, and strains kidney function.^3,17 The National Institute for Occupational Safety and Health recommends workers drink ^24–32 ounces of fluid per hour when working in the heat, 192–256 ounces in an eight-hour workday.¹⁷ The median beverage intake was less than half this amount (68 ounces per day, median 9.4 ounces/hour). Only three workers consumed the NIOSH-recommended 24 ounces or more per hour while working in the heat, only one day each. With the long workdays, high heat, and low fluid intake, almost two-thirds of workers (64%) were dehydrated at the end of the workday. Many workers (45%) start the workday dehydrated, possibly unable to rehydrate sufficiently between one workday and the next. This chronic dehydration may have an enduring impact on kidney function. Multiple studies have reported acute kidney illness among farmworkers.^4,6,9 The damage can be cumulative, as Chicas. et al. observed increasing AKI over three years among fernery workers.²⁴

Most workers preferred to bring their own beverages, including water. If the employers provide water but it is not convenient, not trusted, not consistently available, does not appear clean, or has a bad taste, the benefits of having water provided are not realized. If cool, good-tasting water could be supplied reliably by employers in clean containers and in convenient locations, with sufficient breaks for drinking the water, and clean, easily accessible toilets, workers might have more ability to rehydrate and reduce HRI.

The finding that 11% of workers experienced at least one serious symptom of heat-related illness (dizziness, nausea, vomiting, confusion, cramping, or fainting) on the data collection days indicates the inadequacy of heat precautions. These symptoms, disconcerting in themselves, can also be signs of developing heat stroke or heat exhaustion. As these were measured for three different summer workdays, it is probable that more workers were experiencing at least one episode of these illnesses over the course of the long summer.

California and Oregon, two of the few states with heat-precaution regulations, specify workers in temperatures over 85 degrees should have 10 minutes of rest every two hours.^19,34 The Farmworkers Association of Florida has sought legislation for workplace protections, including 10 minutes of break every two hours for several years according to the organization’s Pesticide Safety and Environmental Health Coordinator Jeannie Economos (personal communication, 2024). The year the proposed legislation did not move out of committee hearings, the same Florida legislators, concerned about the effects of heat on high school athletes, passed legislation requiring school athletic programs to protect players from HRI by monitoring heat stress, modifying athletic activities, implementing cooling zones, establishing hydration guidelines, and having cardiopulmonary resuscitation (CPR) training and automated external defibrillator (AED) capabilities onsite during athletic activity (Florida House Bill 7011).³⁵ This was the same year (2023) two farmworkers died while working in the heat. Legislators decided to protect high school students who chose to participate in athletics while denying protections for the outdoor workforce, blocking outdoor-worker heat protection standards at the county level.

Miami-Dade County was developing outdoor-worker heat-protection regulations when Florida legislators in the 2024 legislative session passed a bill to preempt any local heat protections for outdoor workers, blocking the ability of local governments to require workers’ heat protections (Florida House Bill 433). Agriculture, building industries, and the Florida Chamber of Commerce pressured legislators to block workplace heat-protection requirements.^21,22 While industry has resisted heat-protection requirements, especially mandated rest breaks in heat-risk conditions, the evidence indicates that voluntary adherence to guidelines is not occurring. Protecting the workforce as temperatures continue to rise will require a commitment to humane treatment and clear, enforced regulations.

The guidelines provided by NIOSH are recommendations, not requirements. This study indicates agricultural workers do not have the recommended protections described in the guidelines, contrary to industry groups’ and lobbyists’ claims. The few heat precautions to protect the workers were too few and too meager to be helpful. The biggest gap between the recommendations and real practice was in rest breaks, which did not vary between winter and summer despite hours of extreme heat indices in the summer. This underscores the need for regulations and enforcement of the regulations to ensure workers have sufficient breaks when working in high heat and humidity.

Without regulations and enforcement of those requirements, agricultural workers, and likely other outdoor workers will continue to suffer the impact of extreme heat, with increased preventable illness and death. As temperatures continue to rise, protecting the health of the workforce is imperative. Recommendations are insufficient. We need strong, enforced heat-protection regulations for all outdoor workers.