With the Gulf oil spill largely gone, at least at the surface, you can rest easy that the fifth anniversary of Hurricane Katrina's Gulf Coast landfall won't be marked with a "firecane" or "black rain"—and it never would have been.
Flaming hurricanes and flammable rain are scientifically impossible, according to myth-busting scientists.
Ignited online, the firecane rumor has been covered by publications including New York magazine (read "Firecane!") and debated on Web forums such as Myth-Weavers, where one participant summed up how firecanes might be born:
Hurricane sucks up oil
Lightning ignites oil
But—surprise—the scenario doesn't stand up to scrutiny, according to Jeff Masters, director of meteorology for the Weather Underground website.
In an oil spill, Masters explained, it's the vapors from volatile compounds that burn, not the liquid oil itself. And most of those flammable volatiles evaporate and disperse soon after oil enters the water.
Even at the oil slick's worst this summer, the oil at the surface of the Gulf of Mexico (map) was largely a type of thick crude loaded with "heavy compounds" called asphaltenes, which don't burn easily under any conditions, Masters said.
This summer, for example, BP had a hard time starting even the intentional burns meant to deplete the slick, according to environmental chemist Barry Dellinger. In a marine oil spill, he added, there's simply too much water mixed with the crude to allow for a sustained blaze.
"They actually use napalm to start the burns, or they can't get enough heat," said Dellinger, of Louisiana State University.
(See "Oil Slick May Be Burned to Help Stop U.S. Rig Spill" [April 27].)
Unlike napalm, the slow-burning fuel made infamous in the Vietnam War, "lightning would be a quick strike," he said.
"I wouldn't think that you could have enough sustained heat from that to continue to have oil vaporize and burn."
Even if lightning could somehow ignite a hypothetical oily storm, the fire would quickly be quenched, according to Weather Underground's Masters.
"Hurricane winds and rain chop up the water so much," Masters said. "It would be very hard to sustain a fire in those kinds of conditions."
And that's assuming the oil could make it into hurricane winds and clouds in the first place.
If oil from an ocean spill were to impregnate storm clouds, you might theoretically end up with oily rain turning Gulf cities into tinderboxes. Just this June unsubstantiated videos purported to show "black rain" (for example, "Raining Oil in Louisiana?" on the Huffington Post).
But because seawater must evaporate to reach clouds and possibly turn to rain—and because the floating crude in an oil spill is as hard to evaporate as it is to burn—black rain is pure science fiction.
If a hurricane strikes an oil slick, "the amount of oil that's going to be able to evaporate is very, very tiny," said Chris Landsea, science and operations officer at the National Hurricane Center in Miami.
"So any concentration of oil in the rain would be puny and the rain not much different at all from that found in a regular hurricane."
In addition, the seawater that makes it into clouds—even when an oil slick is present—is naturally clean, Weather Underground's Masters said.
The very process of evaporation filters out impurities, which is why it's used to make distilled water, he noted. "So that's not a good way to get oil into rain."
Oil on Land, Minus the Pyrotechnics
There are ways for an ocean oil slick to end up on land—for example via storm surges, tornado-like waterspouts, and strong winds. (See pictures of oil and tarballs on Gulf beaches in May.)
None of those methods, though, promise fire in the sky or combustible rain.
"The idea of a firecane, or oil raining down from the sky," NOAA's Landsea said, "those are really just impossible scenarios."