Video shows fire in Gulf of Mexico after gas pipeline rupture
youtube.com
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The burning gas will most likely produce less air pollution that the effects of venting gas into the atmosphere. And it's not like they would have to put out the fire on the _surface_ to fix the leak that is likely tens if not hundreds of meters below surface.
Those people have been dealing with oil for decades, and there'a millions of dollars at stake; assume that they know what they're doing.