Jesus Tovar buys all new employees the water jug of their choice before they ever set foot in his fields. One they’re comfortable with, so they regularly use it.

“We have to protect our workers,” said Tovar, a Yuma farmer and Arizona Farm Bureau member. “If they don’t have water, ice and shade, they could get sick.”

Farmers and ranchers have voluntarily provided these things for years, but the push is on to set enforceable statewide requirements.

As that debate solidifies, it’s important to understand what science tells us about working in intensifying heat. 

It can help ensure that Arizona’s standards are as effective for workers as they are practical for employers.

How does heat affect the body?

The hypothalamus — your brain’s internal thermostat — activates the body’s cooling systems to regulate your core temperature. 

Blood vessels widen to rush warm blood to the skin, where it can radiate heat. 

Your sweat glands also kick in, pushing water to the skin’s surface where it can evaporate and pull even more heat from the body.

This is tough work, even when bodies are at rest. The heart beats faster in extreme heat, and blood flow is diverted from the kidneys.

Hydration is crucial to keep this process going, and serious injury or death can occur when the body’s cooling systems can’t keep pace.

How hot is too hot to safely work?

Science hasn’t fully worked this out — in part, because it’s not just the temperature that impacts our ability to stay cool.

Humidity and direct sun exposure can hinder cooling by limiting sweat evaporation and further heating the skin, while wind can help in some circumstances by sweeping heat away.

Individual factors — including age, gender, sleep deprivation, alcohol use and underlying health conditions, such as high blood pressure or diabetes — can also impact a person’s ability to process heat.

There is no set temperature where work is prohibited, but there are federal and state conversations about potentially setting a limit.

Is heat making more workers sick?

There is little evidence that more workers in Arizona are dying or being hospitalized due to heat exposure in recent years, even if cases have skyrocketed across the population.

Last year, the Arizona Division of Occupational Safety and Health investigated two heat-related fatalities on worksites, out of the hundreds that occurred statewide.

Neither involved farm or ranch workers.

It’s less clear how milder cases of heat illness are impacting workers. These have long been underreported.

Meanwhile, researchers are only beginning to scratch the surface about how daily exposure to heat impacts outdoor workers’ health.

There is evidence that prolonged heat exposure can pull resources away from organs, damaging them over time.

A recent study of sugarcane workers in Nicaragua found that regular rest, shade and hydration not only improved worker productivity but also reduced the severe kidney injuries that this population has suffered for years.

How much water and shade are needed?

A wide body of research underlines the importance of rest, shade and proper hydration.

But is it more effective to take a work break outdoors, under the shade of a tent or tree, or indoors in air conditioning?

How often should breaks be taken in these spaces, and for how long?

And what is best for workers to drink: Just cool water? Or a mix of water and electrolytes?

Science is still working through specifics.

“A lot of the guidance comes from humid places,” said Jenni Vanos, an Arizona State University professor studying how extreme heat can impact our health.

“We’re applying the same thresholds here, where it’s dry, and finding that some don’t work as well.”

Why does recovery time matter?

The human body adapts after a week or two of regular heat exposure, sweating faster in the elements to more efficiently remove heat.

But it also needs time out of the heat to recover.

“There is evidence that if workers don’t cool down, hydrate and rest overnight, it could hurt their ability to work the next day,” Vanos said.

Studies suggest that at least 40% of employees arrive at work dehydrated, making it more difficult for them to properly hydrate while working in the heat.

Vanos and ASU researcher Gisel Guzmán Echavarría recently outfitted participants with weather sensors and smartwatches to better understand how people cope with heat in daily life.

The three-part study found that the same heat exposures can impact people differently, and that some experienced heat strain even when they said they felt comfortable.

It also revealed that while most people modify their routines to stay cool, those with the lowest incomes were least able to do so.

This is important context because there are many issues out of growers’ control that can impact a worker’s ability to stay safe in extreme heat.

It also suggests that solutions must encompass more than just employers.

What works best in rural Arizona?

Arizona’s rural population faces higher risks of heat-related illness — thanks in part to underlying health conditions, age or income limiting how often they use air conditioning.

But most research has focused on mitigating heat risk in cities.

Ladd Keith, a University of Arizona professor who studies policies to mitigate extreme heat, has recently begun fleshing out the unique challenges that rural areas face.

“Cities have advanced cooling centers, cool pavement and urban greening,” he said. “But those might not be best strategies for rural farming communities” with little asphalt and wide distances to travel to the nearest cooling center.

In addition, many farm and ranch communities are growing more reliant on temporary foreign labor, a demographic that is poorly understood.

Kate Ellingson, a UA epidemiologist, found that the population is becoming less migratory and more seasonal — and growing rapidly, with crop workers in Yuma increasing nearly 60% over the last decade and a half.

She is using this data to predict which workers face the most heat risk.

“What we’ve found so far is that risk is not episodic or sporadic — it’s really predictable,” Ellingson said. 

“This can help us better understand where and when to direct resources, so we can mitigate that risk.”

Need more help with heat?

Arizona Farm Bureau has developed a tool kit to help farmers and ranchers write a heat illness prevention plan, navigate state inspections and institute heat safety best practices.

Find the tool kit and information about the state’s latest heat guidelines at azfb.org/advocacy.


Joanna Allhands writes about water, land use and other issues important to the Arizona Farm Bureau. Reach her at joannaallhands@azfb.org.