Methane gas-burning appliances leak carcinogenic benzene into homes even when those appliances are turned off, a study published today in Environmental Science and Technology found. The study also found gas appliances and infrastructure in California (including outdoor pipelines) leak an estimated 4 tons, or more, of benzene into the atmosphere every year, as much benzene as 60,000 cars.

Even with gas stoves turned off, the researchers discovered, they continued to leak at least 12 hazardous air pollutants, including “BTEX” chemicals (​​benzene, toluene, ethylbenzene, and xylene), of which the most hazardous is benzene, which is linked to cancers including leukemia and other blood disorders. The risk posed by the carcinogen increases linearly with a person’s exposure; “There’s no safe level of benzene,” Philip Landrigan, a pediatrician and public health professor at Boston College, told the AP.

“Simply opening the windows or turning on a range hood while the stove is on” will not eliminate the risk, Kelsey Bilsback of PSE Healthy Energy, told the New York Times.

Methane, the main ingredient in so-called “natural gas”, traps more than 80 times more heat in the atmosphere than CO2 over a 20-year timespan; buildings are the source of approximately 13% of U.S. climate pollution, mostly from methane gas burned in ovens, water heaters, and furnaces. While the methane gas industry has lobbied against state and local efforts to encourage building electrification, the study’s findings dovetail with those from a similar study in Massachusetts, as well as numerous previous studies finding increased levels of indoor air pollution in homes with gas stoves, and significant methane emissions from gas stoves. (New York Times $, AP, The Hill, NBC)