BISMARCK, N.D. (AP) — Authorities are investigating how a fatal explosion occurred at an oil field business.

A water tanker apparently blew out at JM Oilfield Services near Ross on Saturday.

The Mountrail County Sheriff’s Office says 33-year-old employee Jesse Holmquist was killed in the blast. Another employee was injured and taken to a hospital. Both employees had been working on changing the tanker’s tires.

The sheriff’s department says Holmquist was a resident of Sidney, Montana. He served in the U.S. Marine Corps, worked in the oil fields of North Dakota and Montana and drove a commercial truck across the country.