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Orchard workers used tablets to answer questions about their work and symptoms of heat-related illness. <b>(Courtesy Stacey Holland, PNASH)</b>

Orchard workers used tablets to answer questions about their work and symptoms of heat-related illness. (Courtesy Stacey Holland, PNASH)

Being paid by piece rate, rather than an hourly rate, can increase orchard workers’ risk from symptoms of heat-related illness, a University of Washington study suggests.

For the study, Dr. June Spector and colleagues with the UW Department of Environmental and Occupational Health Sciences surveyed 100 Hispanic orchard workers who were primarily thinning and harvesting green fruit in central Washington between June and September of 2013.

The maximum temperature during the study period ranged from 77°F to 97°F.

The workers, whose average age was 41, answered questions relating to their work the previous week.

The questions were recorded in Spanish on a touch-screen tablet with visual aids and related to work activities, payment methods, hours worked, breaks, work exertion, hydration, and clothing.

Workers were also asked about their health status and use of medications, alcohol, and tobacco.

Increased cardiovascular demands (due to exertion, for example) and heavy sweating (particularly without adequate fluid intake) can lead to a rise in body temperature and a shortage of blood to the tissues, resulting in light-headedness and dizziness.

Almost a third of the workers said they had suffered those symptoms during the previous week.

Although heat rash, cramps, headache, fatigue, and nausea are also symptoms of heat-related illness, they were not included in the study because they can also be caused by factors other than working in the heat.

Of those who reported symptoms, 67 percent were paid piece rate. Previous research has shown that economic incentives motivate workers to labor harder and faster, increasing exertion and metabolic heat generation.

Spector suggests that the risk could be reduced for piece-rate workers by giving them more frequent mandatory breaks, particularly as the temperature increases. She also suggests that a transition to hourly pay could be considered when the temperature reaches a certain threshold.


Of the 30 workers reporting symptoms of heat-related illness, 47 percent had to walk for more than three minutes to get to a toilet (versus only 29 percent of those who did not suffer symptoms).

Spector said distance from workplace restrooms and drinking water can be a barrier to keeping workers hydrated, particularly if the workers are paid piece rate and don’t want to lose wages by stopping work.

“I think we can say from this study that it likely is a good idea to try to make sure the restrooms are located as close as possible to where people are working,” she said, noting that many growers do that.

“But I think in terms of payment, it’s a little more complicated because some workers have told us that they prefer piece rate because they can get paid more, and workers’ livelihoods are important. A balance between that and making sure everyone stays healthy is important.”

Younger workers

In the study, younger workers were more likely to report symptoms of heat-related illness than older workers, as were women.

The average age of those reporting symptoms was 36 compared with an average of 43 for those with no symptoms. Unlike classic heat stroke, which more commonly affects older people, heat-related illnesses associated with exertion can affect young, otherwise healthy workers, according to Spector.

“The older workers may have a lot more experience, and we think it’s possible they may have learned over time, from other workers, ways to adapt to heat exposure and physical work,” she said.

Exertion can raise the body temperature particularly in new workers who haven’t been conditioned to the heat. She suggests that growers expose new workers to high temperatures gradually over the course of about a week.

Buddy system

She also recommends having a buddy system in place so that workers can alert supervisors if their co-workers appear to have symptoms.

“Some symptoms have to do with becoming irritable and not being aware of what’s going on, and it can be dangerous if someone isn’t aware of what’s happening,” she said. “Watching out for each other is a good thing to do, in addition to things the grower can do.”

Wearing light-colored clothing did not appear to reduce the risk of heat-related illness symptoms.

Spector said although the color of clothing did not seem to be a factor in her study, heat exchange can be affected by the type of clothing and its fabric and whether or not layers were removed, none of which were reported in this research. Previous studies have found that workers perceive a benefit of weight loss from sweating when wearing layers of clothes.


Other factors that did not significantly affect the risk of heat-related illness symptoms in this study included: air temperature, additional rest breaks, the worker’s body mass index, and whether a worker took a drink at least every 30 minutes or at longer intervals.

Spector said it was not too surprising that workers without symptoms had been exposed to just as high temperatures as those with symptoms. Exertion can raise the body temperature high enough to cause heat stroke even in cool conditions.

Spector said a limitation of the study was that workers were asked to recall how many breaks they had taken and how much and how often they had drunk fluids during the previous week, and there’s no way to know how accurate these answers were.

Adequate hydration is known to be critical in preventing heat-related illness. Even if workers did take additional rest breaks, there was no information on what they did during the breaks. Did they sit in the shade or were they still moving around, for example?

In her follow-up studies, these factors are being monitored and measured in real time in order to better quantify and understand them. For example, urine tests can indicate how dehydrated a person is.

Spector is also looking more closely into how heat stress affects productivity of workers, which she hopes will generate helpful information for growers.

“We’re looking for the sweet spot where workers are as healthy as possible and as productive as possible, so it’s a win-win situation,” she said. “The more work we do, the more useful information we will be able to give.” •

-by Geraldine Warner

The research was funded by the U.S. National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, through the Pacific Northwest Agricultural Safety and Health Center.