Gas stoves emit benzene equivalent to secondhand smoke

Gas stoves emit benzene at concentrations comparable to secondhand smoke and even at levels that have triggered investigations when detected outdoors, according to a new study. The research adds to the growing body of evidence that gas used in homes poses a threat to human health.

Previous research has identified a variety of hazardous air pollutants that leak from gas stoves when they are turned off, as Gas Outlook reported last year. But a study, published June 15 in Environmental Science & Technology, is the first of its kind to directly measure concentrations of benzene emitted from stoves and ovens while they are operating.

“This is the first study where we actually measured benzene emission rates directly from the stove while it’s on and burning gas. And we found that actually burning gas produces between 70 and 640 times more benzene than the median leakage rate would produce,” Yannai Kashtan, a researcher in the Earth System Science Department at Stanford University and one of the authors of the report, told Gas Outlook. “So, the combustion itself produces way, way more benzene than is in the gas to begin with.”

Researchers from Stanford University and PSE Health Energy, a nonprofit research institute, collected samples from 87 homes across 11 California counties as well as three counties in Colorado.

In about a third of the cases, a single gas burner set on high or an oven set to 350 degrees Fahrenheit led to benzene concentrations above what is typically found in secondhand smoke.

Benzene is a known human carcinogen, with links to leukemia, lymphoma and other blood disorders. “Benzene is a proven human carcinogen. There aren’t that many proven human carcinogens, and benzene is one of them,” Kashtan said.

Routine exposure to benzene raises significant health concerns, experts say.

“We have known for a hundred years that higher doses, the kinds that workers in industries like the petroleum industry, rubber, printing – we’ve known that those exposures are dangerous and cause leukemia,” Dr. Jan Kirsch, a retired hematologist oncologist, who was not involved in the study, told reporters during a press briefing. “There’s growing information that even lower doses, not like those encountered in industry, will also cause these toxic effects.”

She added: “To me, I’m really hard pressed to think of a more powerful chemical cause of leukemia than benzene.”

The researchers found that the pollutants did not stay confined to the kitchen. Benzene drifted to other parts of the apartments and houses, including in bedrooms, where the pollutants lingered for several hours.

Another striking finding was that the amount of benzene emitted in homes included in the study often exceeded those levels observed at the fenceline of oil refineries in California.

Indeed, benzene emitted from a normally-functioning gas stove was measured at levels equivalent to those that have set off public investigations when those concentrations were detected outdoors.

“As a chemist, it wasn’t surprising that we’re getting some amount of benzene, but I was surprised to see measuring concentrations of benzene in bedrooms that, when reported outside, have triggered immediate investigations and public outcry,” Kashtan told Gas Outlook.

In 2020, regulators in southern California began investigating the source of benzene when an air monitor detected a spike in cancer-causing benzene levels near a Los Angeles high school. In a separate incident in late 2019, Colorado regulators came under fire from residents in the town of Greely when air monitors picked up elevated levels of benzene near a school that is located close to multiple oil and gas drilling sites.

The concentrations of benzene detected in those two incidents, which sparked alarm and prompted public officials to take action, were comparable to the levels measured from gas stoves used in homes in the new Stanford study.

Given the measured levels of benzene emitted from gas stoves, and given what is known about the harm that benzene can cause to human health, some negative health effects “must be happening,” Dr. Kirsch said.

“The idea is not, obviously, to cause panic. The idea is that there are risks and we want to reduce them,” she said. But “this study does point out that people have died. Undoubtedly,” she said, adding that unless the problem is ameliorated, people will continue to die.

The researchers said that ventilation — a fan that diverts air from the kitchen to outside the home, or an open window — can help, but does not entirely solve the problem. And many people with gas stoves live in small apartments without good ventilation.

The only obvious long-term solution is to switch to electric induction stoves, the scientists emphasized. “For those in the United States and Europe, for instance, we stopped cooking over coal a century ago because gas was cleaner. And today, I believe we should stop, eventually, cooking over gas because electric is cleaner,” said Rob Jackson, a senior fellow at the Stanford Woods Institute for the Environment, and a coauthor of the study. “Our data shows that induction stoves emit no benzene whatsoever. So, we have a cleaner technology that’s available today.”

The study adds even more weight to the already extensive research pointing to gas stoves contributing to poor indoor air quality. Separate studies show that stoves leak methane, even when they are turned off. Another study links one in eight cases of childhood asthma to gas stoves.

In Europe, research suggests that more than 100 million European households may be exposed to air pollution from gas stoves at levels that would violate outdoor air quality standards. But neither the European Union nor the Member States are regulating the pollutants from gas appliances.

Local and state governments are beginning to respond. In March, air regulators in the San Francisco region voted to phaseout gas appliances later this decade, with the explicit goal of cutting down on outdoor air pollution (although the order exempted gas stoves). In May, New York became the first state to require most new buildings to be all-electric. Meanwhile, more than a hundred cities and counties have banned gas in buildings in one form or another.

The researchers said that building codes that lead to a shift towards electrification make sense.

Gas stoves are “the only common fossil fuel appliance to vent pollution indoors,” Jackson said. “We would never willingly stand over the tailpipe of a car breathing in its pollution, but we do willingly stand over our stoves, breathing in the pollution they emit.”