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Bismarck, N.D. • One worker (from Rock Springs, Wyo.) was killed and two others were seriously injured in an explosion and fire at an oil well in western North Dakota, authorities said.

The McKenzie County Sheriff's Department said 52-year-old Johnny Stassinos of Rock Springs died Saturday afternoon from injuries suffered that morning at a well site operated by XTO Energy Inc. near Watford City.

The department's statement issued Monday said Richard Maheu, 27, also of Rock Springs, and Daniel Montes, 28, of Fruita, Colo., were airlifted to Regions Burn Center in St. Paul, Minn., where they were in critical condition.

The men suffered third-degree burns to 70 percent of their bodies, said Eric Brooks, director of the U.S. Occupational Safety and Health Administration's office in Bismarck.

Authorities said 40-year-old Justin Pyle of Grand Junction, Colo., was treated for minor burns to his face at a Watford City hospital and later released.

The fire was out when emergency workers arrived on the scene Saturday morning, authorities said.

Houston-based XTO Energy is a subsidiary of ExxonMobil. XTO Energy spokeswoman Suann Guthrie said the men were contractors working for companies that do maintenance on oil wells.

Guthrie said XTO Energy has been working with regulators to determine the cause of the explosion.

The men were on a workover rig that's used to perform maintenance at an oil well. An initial investigation found there was a breech in a gas pipe that ignited, state and federal investigators said.

"There was a split in a pipe, and there was an explosion," Brooks said. Investigators were on the scene Monday attempting to find the cause of the breech and the source of the ignition, he said.

Bill Suess, an environmental scientist with the state Health Department, said no oil or gas escaped from the well.

Brooks said it was the first oilfield-related death in North Dakota in the fiscal year that began last August, compared with seven in the same period during fiscal 2015.

Since late 2010, there have been 108 workplace fatalities in North Dakota, including 48 that were oilfield-related, Brooks said.

Crews on workover rigs have among the most dangerous jobs in the oilpatch, he said.

"There has to be eternal vigilance on ignition sources," he said.

OSHA has stepped up inspections on workover rigs in the past few years and has issued 30 citations of violations since 2012 to companies that did not take appropriate safety measures, Brooks said.