Fire in the hole. Crude oil ignites inside a block of solid ice in a laboratory test.

Worcester Polytechnic Institute

Fire in the hole. Crude oil ignites inside a block of solid ice in a laboratory test.

How to Set Fire to Frozen Oil

In the Arctic, climate change means melting ice—and unprecedented access to the oil once hidden beneath it. But with increased drilling comes a greater chance for oil spills in frigid places where the sun doesn’t rise from November to January. Now, a new study explores how petroleum, fire, and ice interact during oil spill cleanups and suggests that oil and (frozen) water do mix—just not in the way researchers expected.

One common method for cleaning up oil spills is called in situ burning, in which technicians set the fuel slick on fire to vaporize its components. This works reasonably well in warm environments like the Gulf of Mexico, where the spilled oil can be corralled inside inflatable booms before being set alight. Because heat makes oil less viscous, it’s easier to ignite. Under those circumstances, 90% of the collected oil can be burned away efficiently, and workers can collect the rest of the residue mechanically.

But no one knows how effective in situ burning would be in an icy environment like the Arctic. Extreme cold tends to separate crude oil’s chemical components and makes ignition more difficult. And even if you get the spill lit, the cold weather makes it difficult to maintain enough heat to keep it burning over many square miles. Natural evaporation also plays a crucial part in traditional, warm-weather spill management, says Chris Reddy, an environmental chemist at Woods Hole Oceanographic Institution in Massachusetts, who was not affiliated with the new work. “In cold weather, evaporation happens slowly. Forty percent of the oil in the Deepwater Horizon spill [in the Gulf] evaporated without any human action, but that wouldn’t happen in the Arctic.”

In the first study of its kind, researchers at the Worcester Polytechnic Institute (WPI) in Massachusetts tested how Alaskan North Slope crude oil would behave when ignited in ice. They created cavities—essentially bowls carved out of solid ice—to mimic the frozen nooks and crannies where oil would hide in polar conditions. Then, they placed small containers of crude oil inside the cavities and ignited them. Researchers predicted the flame would melt the sides of the bowl and icy water would collect at the bottom, pushing the oil closer to the rim. As it melted, the cavity would widen and the oil would eventually spill over and burn off.

That’s not always what happened. The team found that oil actually burned much faster in ice than in other materials. The heat widened the ice bowls and thinned the oil, allowing it to burn more quickly than expected. Although that may sound like good news for spill management, another of the team’s discoveries was more troubling. During the burns, some of the oil expanded sideways and seeped into the ice, the researchers report in an upcoming issue of the Proceedings of the Combustion Institute.

This surprising behavior suggests that if scientists were to try cleaning up a future Arctic oil spill with in situ burning, they might actually make things worse. Bubbles of spilled oil would likely end up “trapped within icebergs” after an in situ burn, says author Ali Rangwala, a fire protection engineer at WPI. The sooty residue would be unrecoverable until the ice melted, perhaps months or years later.

“I don’t think anyone has thought of the effects of oil seeping into ice cracks before,” says Michael Gollner, a fire scientist at the University of Maryland, College Park, who was not involved in the study. “This suggests a practical way to measure the situation and decide if in situ burning is the best option for managing” an Arctic spill. Adds Reddy, “It’s the first step into uncharted waters”—one that may be put to a real-world test very soon.

Posted in Chemistry, Environment