LENNOX, S.D. (AP) — The State Fire Marshal is investigating an explosion that injured two workers changing a gas line outside of a Lennox utility company.

Police Chief Orville Jorgensen says a leak occurred as the Farm Gas Co-op workers were working on the business' gas line Monday afternoon. The Argus Leader reports 56-year-old Ernie Erickson and 37-year-old Christopher Kuper were near an entrance when the explosion happened and the building caught fire.

The men were taken to a Sioux Falls hospital and later airlifted to a Minneapolis burn center. Jorgensen says Erickson and Kuper are recovering from second- and third-degree burns.

Jorgensen says it's still unclear what caused the explosion, but authorities believe the leak was ignited by something inside the building.

He says the building's east side was destroyed in the fire.

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