Although it sounds absolutely bonkers, a common technique for cleaning up oil spills is burning as much as possible, then scooping up the residue. Trying the same technique in Arctic conditions is complicated, burning faster but hiding sooty residue within the ice.

Testing in situ burning in icy conditions. Image credit: Worcester Polytechnic Institute


If an oil spill occurs in temperate climates like the Gulf of Mexico, one of the go-to methods of cleaning it up is to light the spill on fire. It burns a good chunk of the fuel, and self-extinguishes when the layer gets too thin. Mechanical methods are then used to try to skim off the remaining spill.

But taking the same techniques north have an added complication: ice. Ice is a complex surface, full of pits and cavities where oil can get trapped. To test out the technique of in situ burning in Arctic environments, researchers at the Worcester Polytechnic Institute in Massachusetts and the University of Edinburgh in the United Kingdom ran a series of experiments. "In situ burning" just means burn it where it is, lighting the oil on fire where ever it happens to be.


Top view of cavity expansion during in situ burning. Image credit: Rangwala et al.

The basic premise was to carve bowls out of ice, added oil, light the fuel on fire, and watch what happened. They ran the same experiments with variations on a theme, testing the impact of cavity size from 5 centimetres to over a meter diameter, and the type of fuel from crude oil to high octane.


Cross-section of cavity expansion and meltwater growth during in situ burning. Image credit: Rangwala et al.

Unsurprisingly, the heat of the flame melted the ice, expanding the cavities. The expanding cavity diameter and increasing volume of meltwater thins the oil layer and buoys it up, causing the fuel to burn faster. The fuel keeps burning until either the oil reaches a critical thickness (around 3 millimetres) or melts a channel out of cavity and spills out, self-extinguishing the flame. So far, so good: the burning technique works even faster in Arctic conditions than in the balmy Gulf of Mexico.

But, there's a catch. Two, really.


In situ burning of fuel trapped within a 1.1 meter square cavity. Image credit: Rangwala et al.

For larger cavities, anything 25 centimetres in diameter or greater, the flames can boil over in a downright intimidating tower of flame. The large scale test with a 1.1 meter by 1.1 meter square cavity managed to lick so high with such an intense heat flux that it scorched some of the laboratory equipment! But while it looks totally freaky, and would very likely upset any creatures in the vicinity, this alone isn't enough to nix the technique.


Lateral cavity grow in all sized cavities, trapping oil within the ice. Image credit: Rangwala et al.

Something worse is hidden in the final point of the conclusions: as the cavities expand, they grow sideways under the ice surface, developing a trapped lateral cavity. The lateral cavities trap 10 to 35% of the crude oil inside the ice, where it neither burns off nor can be mechanically collected until the ice melts. The sooty residue can be incorporated into the ice, further complicating the situation. Burning oil in situ in icy conditions is not only just less effective as a spill cleanup mechanism as it is in temperate climates, but it also directly creates a more complicated mess that defies cleanup at all.

Overall, this sounds like a very bad idea.

Tip via Science Magazine. The results are in Proceedings of the Combustion Institute, and available here [open access].