Sustainability Energy

Even when off, gas stoves can leak benzene concentrations comparable to secondhand smoke

“Most of these leaks that we're measuring are so low that you would not be able to smell it.”
Gas stove

Story at a glance

  • A new study carried out by PSE Healthy Energy, a nonprofit research institute, highlights different levels of benzene found in gas stove leaks measured when the appliance is turned off.

  • Benzene is a known human carcinogen that has been linked with leukemia and other blood cancers.

  • Ninety-nine percent of the samples collected from California homes contained some level of benzene.

Leaks of unburned gas from stoves can contain benzene concentrations comparable to secondhand tobacco smoke, according to new research from PSE Healthy Energy. The indoor leaks of benzene, a carcinogen, and other hazardous air pollutants pose health risks to humans and in some cases exceed safe exposure levels. 

The study was published in the ACS journal Environmental Science and Technology. To carry out the research, investigators analyzed 185 unburned natural gas samples from 159 residential gas stoves across different regions in California.

“Just having a gas stove in your kitchen can create benzene concentrations comparable to the benzene found from secondhand smoke, but any additional amount of benzene leaked into your home from gas appliances is not good,” said lead study author Eric Lebel in a press briefing. The risk of adverse health effects from benzene rises as exposure increases. 

A total of 12 hazardous air pollutants were detected, with concentrations found in every sample collected, though levels varied based on region and gas utility employed. 

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Benzene was detected in 99 percent of samples, with average concentrations ranging from 0.7−12 parts per million by volume (ppmv) and a maximum of 66 ppmv detected. 

In comparison, the California Office of Environmental Health Hazard Assessment’s eight hour reference exposure level for benzene — a point where no adverse health effects are anticipated — is just 0.94 ppb. 

“We found that the leakiest stoves coupled with the highest benzene concentrations can exceed this level in California by up to seven times in indoor air just from benzene from gas stoves leaking while they’re off,” Lebel said. 

“Most of these leaks that we’re measuring are so low that you would not be able to smell it,” he added, noting the only way to completely eliminate the health and environmental risks is to get rid of gas. 

Because the study only measured leaks when stoves were off, estimates are likely conservative, authors said. Opening a window or turning on a hooded vent only when a stove is in use may not be sufficient to reduce air pollution.

The extra benzene leaks— estimated to equal annual emissions from nearly 60,000 light-duty gasoline vehicles— are currently not included in any statewide inventories. The pollutant, along with other non-methane volatile organic compounds, contributes to ozone formation, exacerbating smog and fine particulate matter pollution.

Previous research also carried out in California found methane and nitrogen oxide leaks from gas stoves into kitchens when they’re in use, when they’re off and during ignition and extinguishment. These leaks were also not detectable by scent. 

Eighty-eight percent of homes in the state use natural gas and based on the most recent findings, those with gas stoves could be continuously exposed to the pollutant. However, homes’ ventilation rates and kitchen sizes can also affect benzene concentration levels.

Benzene can cause leukemia and other cancers of the blood cells. Exposure can also lead to anemia, low blood platelet count and a low white blood cell count in the long term.

The highest levels of benzene were recorded in Los Angeles County. Measurements in surrounding regions including North San Fernando and Santa Clarita Valleys showed concentrations 30 times higher than the state average.

Both valleys are situated near a storage facility of SoCalGas, which made headlines several years ago when a leak was discovered in October 2015. Although the well was sealed in February 2016, the event marked the largest gas leak in U.S. history.

“Now we can only really speculate as to the cause of the elevated [benzene] levels in these areas. But it really is in these areas where we have the greatest concern for impacts to indoor and outdoor air quality,” said study co-author Drew Michanowicz. 

California mandates labels to appear on gas containing warnings about harmful ingredients, and utility companies cite these risks on their websites. But gas stoves do not contain this warning.

The findings come amid a push to transition away from natural gas powered appliances. In September, California moved to become the first state to ban natural gas heaters and furnaces, while several cities in the state have already banned gas stoves in new residential and commercial buildings. 

Natural gas has often been touted as a clean transition fuel that can help wean the country off non-renewable energy sources. And although the burning of natural gas does emit less carbon dioxide compared with that of other fossil fuels, methane leaks throughout the extraction, production and distribution processes pose risks environmentalists say could set back the fight against climate change. 

Methane is also the second most abundant greenhouse gas caused by human activity, according to the EPA, and is 25 times as potent as carbon dioxide at trapping heat in the atmosphere. 

“It is difficult to draw any conclusions from measurements from 159 homes in one state when there are more than 77 million residential, commercial and industrial natural gas customers in all fifty states,” said the American Gas Association in response to the study’s findings.

“The study relies on questionable assumptions about the air change rate (the frequency of the air being replaced in a room) that are inconsistent with typical homes based on current U.S. Environmental Protection Agency literature.”

The AGA continued, “Most model simulations—including all median value simulations—did not result in ambient benzene concentrations attributable to emissions of natural gas from stoves that are above the California Environmental Protection Agency Office of Environmental Health Hazard Assessment (OEHHA) 8-h REL of 0.94 ppbv (also equal to the chronic REL). In a few cases, cascading worst-case assumptions led to questionable results unsuitable for public policy determinations.”

Editor’s note: This story was updated on Oct. 21 with a statement from the American Gas Association.

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