The National Transportation Safety Board is investigating a ruptured natural gas pipeline that exploded into dramatic flames Sunday, stopping a Union Pacific Railroad train carrying hazardous materials in its tracks west of Cheyenne. The fire broke out near the same location as a Union Pacific train, leading some callers to report that the train itself was ablaze. Union Pacific spokesman Mike Jaixen said in an email Monday that the train halted about 40 feet from the rupture. With help from three fire agencies in Laramie County and Cheyenne, firefighters quickly contained the blaze. The cause of the explosion is under investigation by Union Pacific Railroad and the NTSB, according to the Laramie County Sheriff’s Office.