Federal investigators say an explosion and fire at a southeastern Oklahoma natural gas well that killed five workers followed the removal of pipe from the well but that an ignition source still hasn't been identified.
Officials from the U.S. Chemical Safety and Hazard Investigation Board updated the status of their investigation Thursday into the Jan. 22 blast in Pittsburg County near Quinton, about 100 miles (160 kilometers) southeast of Tulsa.
Lead investigator Lauren Grim says officials are testing a blowout preventer on the rig that failed to close prior to the explosion. Officials say it may take a year before their investigation is complete.
The explosion was the deadliest drilling accident since the Deepwater Horizon drilling rig exploded in the Gulf of Mexico in 2010, killing 11 people.