Investigators on Monday were probing the cause of a weekend refinery fire in St. Paul Park that killed a Hastings man.

"We're doing everything we can to establish the cause and make every effort to make sure a tragedy like this doesn't occur again," said Robert Calmus, a spokesman for Marathon Petroleum Co. "We definitely take safety first."

The body of Nick Gunter, 29, was found Sunday inside a 10,000-barrel fuel oil tank. The fire began after an explosion at 8:30 a.m. Saturday.

"It's a sad and unfortunate incident these past couple days, losing an employee; it's really tough to accept," said John Hunziker, mayor of St. Paul Park.

An inspector for the state Occupational Safety and Health Division was at the refinery Monday, said spokesman James Honerman. Minnesota OSHA also is investigating a Sept. 27 incident involving three employees taken to a hospital after a chemical spill, he said. The agency hasn't reached any conclusions in either case, he said.

Last spring, Marathon paid a civil penalty of $60,000 to the Minnesota Pollution Control Agency for air quality violations at the refinery. Those violations, which Marathon voluntarily reported to the MPCA, included several tons of a clay-based catalyst deposited over St. Paul Park, Newport and Woodbury in 2004, and emissions violations of carbon monoxide, sulfur dioxide, hydrogen sulfide and nickel between 2003 and 2006.

The refinery has no current enforcement actions, said Suzanne Venem, a MPCA compliance officer.

"We would be interested still in what the cause of the fire was and whether it was preventable," she said. "When you have black smoke, you have air pollution."

The refinery produces 70,000 barrels a day and processes crude oil into gasoline, diesel, fuel oil, jet fuel, propane and asphalt.

Teamsters Local 120, the union that represents about 200 workers at the refinery, wants to know more about the cause of the explosion, said spokesman Brad Slawson Jr. He said the nature of the work is dangerous, in any case.

"It's an unsafe environment," he said. "I don't care how well the company has it running, they're refining gasoline."

Gunter was a union member, Slawson said.

Hunziker, the mayor for the past 10 years, said the city wants to know whether the explosion resulted from mechanical or human failure. He said that each owner of the refinery, dating to when it opened in 1939, has followed a strict safety regimen considering "these types of materials" processed there.

"All in all their safety record is pretty admirable for the quantity of the product they handle every day," he said.

Calmus said Gunter's death was the first at the refinery under Marathon ownership. The last fatal accident was on Nov. 30, 1978, he said.

Kevin Giles • 651-298-1554