[img]http://d.yimg.com/a/p/afp/20100426/capt.photo_1272213602947-2-0.jpg?x=130&y=72&q=85&sig=2PSMg0r_0cZ4Oznrszw.8g--[/img]AP - Racing against a threat to environmentally sensitive marshlands, authorities planned to begin Wednesday burning some of the thickest oil from a rig explosion off the coast of Louisiana.