Thinking of building a backyard bonfire to keep you warm on these chilly winter nights? You’re not alone. Humans seem to be a bit of a pyro species, if recent headlines are any indication. This year we’ve seen massive piles of stuff burning in the news—though it’s usually less about warmth and more about political and emotional impact. Kenya, for example, torched 105 tons of illegal ivory and more than 5,000 seized firearms to make a point. These dramatic images of smoke and flame speak volumes, sending a powerful image into the skies.
But what are the environmental and human health impacts of burning massive piles of stuff—especially when it’s stuff that isn't normally meant to be burned? Smithsonian.com reached out to the U.S. Environmental Protection Agency to find out.
Open burning of any kind is generally bad for humans and the nearby environment, EPA press officer Cathy Milbourn said over email. Compared to controlled burning, such as in boilers, large outdoor fires tend to produce "highly mutagenic and carcinogenic emissions" that can affect any humans hanging out in the vicinity. (Mutagenic chemicals, as the name suggests, are those that tend to cause genetic mutations.) The fine particles in smoke, meanwhile, can find their way into eyes and lungs and cause bronchitis, as well as aggravate existing conditions like heart and lung disease
Temperature matters. If the fire is hot enough, many of the toxic molecules will break down into simpler, less toxic ones. But open fires rarely reach those temperatures, meaning toxic molecules are released as a gas that can easily find its way into lungs and the environment. As opposed to high-temperature incinerators, bonfires also tend to produce more carbon monoxide, which is harmful when breathed in and can form toxic ozone. As Milbourn puts it: "It almost doesn’t matter what you burn but, instead, how you burn it."
From an environmental perspective, the smoke from any bonfire—including normal ones built with wood or paper—adds particulates and carbon to the atmosphere, Milbourn said. These can act not only as air pollutants, but also as "climate forcers," meaning they can contribute to climate change in the short or long term—albeit on a much smaller scale than industry or automobiles do. Particulate pollution can lead to lung and nose irritation, and possibly even lung cancer if exposure is severe and prolonged, according to the Centers for Disease Control
Ash from bonfires can also easily run off into rivers and lakes, introducing chemicals and possibly altering the pH of the watershed. This could cause the widespread of fish and other animals living in or near the watershed.
Some people are more creative with what they burn. Recently, the son of the Sex Pistols’ manager set more than $6 million worth of punk paraphernalia—rare records, clothing, concert posters—aflame on the River Thames in protest of a mainstream punk celebration. (Ironically, the event ended with a plea the crowd to support green energy.) Specific tests on these objects haven't been done, Milbourn concedes, but burning most kinds of plastics or metals is a quick path to creating for those close-by, or even farther if there’s wind. "The potential for adverse health effects goes up because these are inherently toxic [molecules]," she says.
Some of the worst items to burn in terms of toxic emissions include manmade chemicals like Teflon or many plastics, used motor oil and rubber such as that found in tires, Milbourn says. On the more natural side of things, burning poison ivy can be very harmful to people allergic to it, she says, while burning cannabis plants could have some "anticipated effects if you are downwind." But the danger here is relative: Compared to burning a massive pile of truck tires, lighting a small bonfire in your backyard with friends and s’mores seems like a pretty reasonable risk to run.