Shamim Ahamed and Purvi Tiwari, who lived on opposite sides of the world, were exposed to the uncomfortable conditions they encountered during their PhD research in greenhouses. This inspired them to study the heat inside the spaces.
Tiwari, a researcher at India’s Indira Gandhi Agricultural University, realized that the heat-boosting effect of greenhouses was a major concern that needed to be studied because she herself experienced the leg cramps, nausea and dizziness that her farmers later described. Outdoor summer temperatures in parts of India can reach 120 degrees Fahrenheit (50 degrees Celsius), leaving greenhouse workers “feeling suffocated inside.” She added that greenhouses have become a trend in the past five years as available land shrinks due to development.
“Workplaces should not harm people,” she said. “If that work area is harming that person, that means it’s not a good place to work. That needs to be changed.”
In the United States, the latest agricultural census shows that the number of greenhouse and nursery workers in the U.S. has increased by 16,000 in recent years. But there are no federal heat regulations, even as greenhouses have become increasingly popular and the number of workers in them has increased. There has also been minimal research into the experiences of workers and their broader working conditions, or into how to protect those who work in their often hot and humid environments. But academics around the world, like Tiwari and Ahamed, are working to fill the knowledge gaps about the unique conditions greenhouse workers face.
Bharat Jayram Venkat, associate professor and founder of UCLA’s Heat Lab, said that “there has been a lot of research done on agricultural workers … but not specifically on greenhouses.” Most of the literature focuses on maximizing plant growth and production in greenhouses, not on human health.
“On the surface it makes sense — that’s what greenhouses are for, really. But of course you need human workers in those greenhouses to make them work,” he said, “so you have to think about people’s health.”
More heat, more greenhouse workers
Last year was the hottest on record, with cities across the U.S. repeatedly experiencing temperatures above 90 degrees. According to the U.S. Department of Agriculture, the number of farms and square footage under glass, and the value of greenhouse and nursery sales, all increased compared to 2017. Additionally, use of the H-2A farmworker program essentially doubled between 2010 and 2019, impacting workers’ ability to complain about extreme heat.
Venkat expects more research to come as indoor climate-controlled growing environments likely become more popular as climate conditions become less predictable and more extreme. Laws such as California’s recently passed indoor heating regulations and the increase in greenhouse workers will also increase interest in studying them, he said.
Jennifer Vanos, an associate professor at Arizona State University, has been studying the limits of survival and physical work capacity in extreme heat. Using research led by a former fellow at Loughborough University — which assessed how the body functions under varying temperatures, wind speeds, humidity and radiation — Vanos and colleagues studied the productivity of farm workers on a warming planet.
One of their findings was that the warmer it gets, the less productive workers can be, which has economic implications. In the context of agriculture, that could mean fewer crops are harvested and more workers are needed.
Ultimately, their results showed that “people need to lower their heart rate to work safely, which means they need to lower their exercise output to perform the same tasks in a warmer environment,” Vanos said.
Signs of heat stress include heavy sweating, cramps, and a rapid heart rate. Exposure to extreme temperatures can increase the risk of injury from dizziness, weakness, or fainting. And heat stroke, the most serious heat-related illness, can occur when the body stops sweating and the temperature rises.
When heat combines with humidity, it becomes more difficult for sweat to evaporate to cool the body, creating more dangerous situations.
“If the air is already really saturated with water vapor … the ability of sweat to evaporate is greatly reduced,” Venkat said. “That means your risk of heat-related illness or even death is going to be much higher.”
Filling research gaps
Researchers Tiwari and Ahamed have now published papers on greenhouse environments. Ahamed, now an assistant professor in the Department of Biological and Agricultural Engineering at UC Davis, studied the risks of heat exposure in high-tech greenhouses and compared the effects on workers when tools like shade covers are used in greenhouses to keep temperatures cooler. Tiwari spoke to workers in India who reported nausea, drowsiness and dehydration, and she and her team found that greenhouse workers who worked in the middle of the day had an average heart rate that was 20 percent higher than those in open fields.
Ahamed said Tiwari’s research is relatively rare. Many of the studies that do exist are in countries outside the U.S. And even when studies are U.S.-based, it can be difficult to find a good sample size for greenhouse workers in particular.
For example, researchers at UC Merced found higher rates of preterm birth, low birth weight and birth defects among pregnant farm workers in general, including field and nursery workers. A study from Iran found similar effects among greenhouse workers there, but the UC Merced team said they didn’t have enough pregnant indoor farm workers to look at that outcome alone.
The gaps in the literature, Ahamed said, have led to “a huge gap in how these things can be regulated or standardized in some way.” He thinks there should be building codes based on UV exposure, heat and humidity, as well as safety procedures for workers inside.
But with such a wide range of greenhouse technologies in use – from mega-farms spanning many acres to microclimates created with “high tunnel” or “arch greenhouse” setups that bend plastic over small sections of a field – the patchwork of possible options remains a problem when implementing standards.
However, he thinks it would be feasible to have different protocols depending on the type of greenhouse.
“That’s why they need to do research and make recommendations,” Ahamed said.
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