AP: An offshore petroleum rig exploded and was burning Friday in the Gulf of Mexico about 80 miles south of Vermilion Bay. The Coast Guard says no one was killed in the explosion, which was reported by a commercial helicopter flying over the site around 9 a.m. CDT. All 13 people aboard the rig have been accounted for, with one injury. The extent of the injury was not known. Coast Guard Cmdr. Cheri Ben-Iesau says seven Coast Guard helicopters, two airplanes and three cutters were …