Hot weather may be the work environment for the 1.4 million farmworkers in the United States who harvest crops, but new research shows that these workers continue to experience excessive heat and humidity even after leaving the fields.

Wake Forest Baptist Medical Center researchers conducted a study to evaluate the heat indexes in migrant farmworker housing and found that a majority of the workers don't get a break from the heat when they're off the clock.

Lead author Sara A. Quandt, Ph.D., a professor of epidemiology and prevention at Wake Forest Baptist, said the findings raise concerns about productivity and worker health.

"We found that a majority of the workers are not getting much respite from the heat in the evening," she said. "While we didn't measure direct health outcomes, the research raises concern about worker's health related to dehydration and sleep quality, which can, in turn, impact safety and productivity."

The study, which appears online this month in the American Journal of Public Health, is part of an ongoing program of community-based participatory research at Wake Forest Baptist in conjunction with the N.C. Farmworkers Project, Student Action with Farmworkers and other clinics and organizations that serve farmworkers in the state. Quandt and colleagues have also looked at water quality, housing conditions and occupational safety in migrant farm camps.

For the study, the researchers assessed heat index in common and sleeping rooms in barracks, trailers and houses at 170 eastern North Carolina farmworker camps in 16 counties across a summer from June 15 to Oct. 4, 2010. Heat index was calculated in the evenings using the standard equation to determine varying risk levels ranging from no danger (heat index< 80 F) to extreme danger (heat index> 115 F). The average age of workers was 35.2 years.

More than half of the workers, 55 percent, reported no air conditioning in the dwelling; 7 percent reported central AC, and 38 percent reported window AC. Use of electric fans in sleeping rooms was reported by almost 80 percent of workers. Most heat index measures in the common and sleeping rooms exceeded the danger threshold, according to the study results.

"If you sleep in a very hot room, you don't sleep well and you don't get rested so the quality of sleep is compromised," Quandt said. "For workers, the concern is what happens in the daytime during work hours while using tools and machinery. They're in situations where they have to make decisions that can affect safety, but if they're drowsy, this can be an issue."

Quandt said it's also important to put the study into context regarding an increasing concern in the occupational health arena regarding global warming climate change. She said there is a large, international body of literature now projecting what the health effects of global warming are going to be on workers and national productivity. "There is historical data to show that temperatures in the southern United States have risen," she said, "and over the long term, warmer temperatures are going to strain workers who do a lot of physical labor and affect their productivity."