The Pennsylvania department of environmental protection announced this week it would spend $1.4m to put out a several-year-old fire near the Pittsburgh International Airport that now threatens to disrupt air travel and cause an explosion at a major gas pipeline.

A years-old fire may sound extraordinary, but underground long-burning fires are relatively common in the state, thanks to Pennsylvania’s abundance of abandoned coal waste piles and closed underground mines. The coal in those piles and mines act as a readily ignitable fuel source, should a stray ember from a cigarette land or a lightning bolt strike in the right place.

While most don’t pose an immediate threat to human safety, some, like the one at the Pittsburgh airport can. And the ones that are not an imminent danger are nonetheless concerning for environmental regulators who say the piles and mines have the potential to leach toxins into soil and groundwater, and contribute unnecessary carbon dioxide to the world’s already overburdened atmosphere when they catch fire.

“It’s the leftover heritage of the mining era, and it’s something that we have to deal with now,” said John Poister, a community relations coordinator in the Pennsylvania department of environmental protection’s Pittsburgh office. “They don’t catch fire often and usually the fires are relatively isolated, but eventually we’re going to have to put them all out.”

Facebook Twitter Pinterest Signs point visitors toward a fire that has been burning for decades in Centralia. Photograph: Erin McCann/The Guardian

The mines and piles of waste date back to an age when the coal industry operated largely without oversight in the state. Coal that companies deemed unprofitable to burn was often left in massive piles next to mine sites, and the mines were closed without any environmental remediation.

Because of that, no one knows exactly how many abandoned mines and coal piles there are across Pennsylvania, though the number is well into the dozens.

Regulators also don’t know who owned the coal pile next to the Pittsburgh airport. DEP officials believe that one is related to a mine that closed in 1939. The fire there may have started as many as seven years ago, perhaps because of a lightning strike. It hasn’t posed a threat to planes or a nearby pipeline yet: at this point it’s only causing wisps of smoke to escape from the ground. But there’s concern among DEP officials the fire could spread to another nearby coal pile, potentially endangering the pipeline, and causing navigation issues for planes.

“Airports are generally not a good place to have a smoky underground fire,” Poister said.

Not many places are good places for a smoky underground fire, but with limited resources and limited records, Poister said his agency has to prioritise the fires it attempts to extinguish.

“There are people who work around the world in mines and the [coal] piles are right there outside their houses. There’s smoke all over the place and people get sick from the gases,” said Glenn Stracher, a professor of geology and physics at East Georgia State College who has studied coal fires across the globe. “It’s not as visible a disaster as a tsunami or hurricane, but it’s still a worldwide phenomenon.”

Facebook Twitter Pinterest A group of young men explore a large crack in PA Highway 61, caused by the underground coal fire. Photograph: Don Emmert/AFP/Getty Images

While the consequences of mine and coal fires are more dire in less-regulated countries, the fires do occasionally wreak substantial havoc in the US.

Perhaps the most infamous coal fire in history was in Centralia, Pennsylvania, a rural former mining town about three hours’ drive from New York City. In 1962, after years of residents using an abandoned mine shaft as their personal waste dump, some of the waste caught fire, fell into the mine below and ignited a coal deposit several hundred acres wide.

After poisonous coal gases began seeping into the basements of several Centralia residents’ homes, the US government began offering buyouts to the town’s thousand-plus inhabitants in the mid-1980s. Today only a handful of people remain in the town.

The Centralia fire sparked international interest and the site has become a tourist attraction for ghost town explorers. Centralia even inspired the 2006 horror movie Silent Hill.

But for some residents of Pennsylvania, the fire was just another chapter in the coal industry’s storied history in the state.

“It’s kind of sad to look at the town now, but it’s not the first place it ever happened and it’s probably not the last,” said Tom Dempsey, a former postmaster for the town who now lives a few miles away. “You kind of just move on.”