WILLISTON -- A 20-year-old man died earlier this week at a well site 5 miles south of Williston.

Zachary Buckles, of Glasgow, Mont., was found unresponsive at the site and died sometime between late Sunday night and about 5 a.m. Monday, OSHA area director Eric Brooks said.

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The state medical examiner found no obvious signs of the cause of death, but it is awaiting lab results for hydrogen sulfate levels, according to a McKenzie County Sheriff’s Department release.

Since Buckles was found over the open cover of a crude oil tank, “it is believed that he died as a result of H2S gas exposure,” the department said.

Buckles was apparently performing tank gauging operations at the time of his death. He was employed by Black Gold Testers, a subcontractor on the Continental Resources-leased site. Continental spokeswoman Kristin Thomas Miskovsky confirmed in an email that Buckles was a flowtester working on a Continental wellsite.

An OSHA investigator was on site Monday.

This is the 38th oilfield death investigated by OSHA since fiscal year 2010, Brooks said.

The original report was for a party trapped under a rolled-over semi truck, according to the sheriff’s department release.

“It was discovered upon responders’ arrival at the scene that the incident was not a traffic crash, but was in fact a deceased male on top of a tank at an oil location,” according to the department.