Gas appliances could be leaking up to 21 hazardous pollutants in your home

The human health hazards of gas leaks are still relatively unknown. 
Person in brown sweater with a white apron frying something on a gas stove that's leaking methane
Try to keep your home ventilated when using a gas stove or other natural gas appliance. Annushka Ahuja/Pexels

People use natural gas every day in their homes with kitchen stoves, furnaces, and heaters. The powerful fuel behind all of these appliances? Methane.

When methane leaks, which it often does, it can have a hefty impact on the environment. The gas has around 80 times the warming power of carbon dioxide for its first 20 years in the atmosphere, and methane emissions from oil and gas basins can be seen from outer space. Methane leaks can also pose a serious health hazard, as they sneak toxic pollutants and gasses like toluene, benzene and hydrogen sulfide into the air.

But exactly what pollutants are natural gas appliances spreading around people’s homes? That has been a bit of a mystery. 

“It’s a really potent climate pollutant because it’s leaking everywhere, and everywhere we look, it seems to be leaking more than we think,” says Drew Michanowicz, a visiting scientist at Harvard University’s Center for Climate, Health, and the Global Environment. “We just kind of wanted to know what else is in this natural gas considering it is so widely used.”

Michanowicz and other researchers from the Harvard T.H. Chan School of Public Health recently discovered that unburned natural gas from leaks contains nearly 300 unique chemical compounds—21 of which are federally designated as “hazardous air pollutants.”  For the study, which was published today in the journal Environmental Science and Technology, the team surveyed around 70 different kitchen stoves and building pipes in Boston, Massachusetts. What they found was that these samples contained varying amounts of hazardous air pollutants, including benzene, toluene, ethylbenzene, xylene, and hexane. The levels varied based on the time of year, with winter typically having the most pollution.

[Related: Gas stoves are bad for the environment—but what if the power goes out?]

The authors further concluded that the average person probably can’t smell every gas leak, especially the small, slow seeps. Natural gas is naturally odorless, so to help warn residents of leaks, gas companies often mix in an odorizer like methyl mercaptan (a separate compound from methane). This chemical is what gives gas leaks their fart-y, rotten-cabbage smell. 

Still, the researchers found that leaks with up to 10 times the amount of naturally occurring methane inside a building can still be hard to sense. “We don’t have anything [for methane] like a carbon monoxide detector or a smoke detector or sometimes a radon detector. Really, our line of defense for knowing there’s a leak in and around us are those odoring chemicals that they add,” says Michanowicz.  

What this means for human health is still up in the air—but Michanowicz notes that some of the harmful substances such as benzene are already in people’s homes because of other fuel sources and products. The next step for researchers is to calculate the baseline levels of everyday exposure with and without gas leaks, and see what toll that may have on human health. Too much benzene, for example, can lead to short-term symptoms like dizziness or vomiting and long-term illnesses like anemia.

Meanwhile, for folks using natural gas appliances, this study is just another reminder to keep your home as well-ventilated as possible. Opening windows and turning on an exhaust vent while cooking are both ways to make sure potentially hazardous air is continuously flushed out. If you’re interested in moving away from natural gas in your home, electric stoves and other appliances can be an option. Cities across states such as California, Massachusetts, and New York are already starting to ban new gas hookups in buildings

[Related: Two new bills could help pump up a climate-friendly system for heating and cooling homes]

“If climate change is vastly approaching, we already have really good reasons to try to reduce leakage of the methane that’s in natural gas,” Michanowicz says. “Here’s another reason to get us moving and thinking about different ways that our energy system may be harming us that we aren’t aware of.”