PITTSBURG COUNTY, Oklahoma - Autopsies show five men killed in a natural gas rig explosion in southeastern Oklahoma died of burns and smoke inhalation.

The state medical examiner's office report classifies each death in the January 22 blast as an accident.  

The blast occurred in Pittsburg County near Quinton, about 100 miles southeast of Tulsa.  It killed: Matt Smith of McAlester; Parker Waldridge of Crescent; Roger Cunningham from Seminole; Josh Ray of Fort Worth, Texas; and Cody Risk of Wellington, Colorado.

Survivors and estates of the five men have filed wrongful death lawsuits.

An initial state regulator incident report indicates that the blast happened when an uncontrolled release of gas caught fire. 

The Associated Press contributed to this report.