UNION MILLS, Ind. (AP) -- An explosion at a grain silo in northwestern Indiana left one worker dead Monday afternoon, authorities said, and workplace safety officials immediately launched an investigation.

The explosion occurred in a concrete grain silo at the Union Mills Co-op, the LaPorte County Sheriff's Department said in a news release.

The victim was a co-op employee believed to be working in the silo when the blast happened, the department said. The victim's name was not immediately released.

All other employees were accounted for and no other injuries were reported. The cause of the explosion was not immediately clear, the department said, though it said no hazardous chemicals were involved.

The co-op, located about 50 miles southeast of Chicago, has multiple grain and fertilizer storage facilities, Deputy Sheriff Neil Lachmund said.

The Indiana Occupational Safety and Health Administration is investigating, spokesman Bob Dittmer said. It has no record of any inspections at the co-op, he said.

Purdue University farm safety expert Steve Wettschurack said concrete silos can be very dangerous because they seal so tightly. Grain dust is highly volatile, and a small spark, even from someone using a hammer, can set off a blast, Wettschurack said.

"It'll shake the countryside. There's a lot of power to it. But there's not really a lot of fire to it," he said.

The U.S. Occupational Safety and Health Administration website says more than 500 explosions in grain-handling facilities across the nation over the last 35 years have killed 180 people and injured more than 675. Grain dust is the main source of fuel for explosions in grain handling, the website said.

The co-op is owned by Co-Alliance, an Avon, Ind.-based farmer-owned supply and marketing cooperative serving rural communities in Indiana, Ohio and southern Michigan.

Shawn Lambert, safety manager for Co-Alliance, said he was traveling to the explosion site Monday. He said he did not know how many workers were on-site at the time of the blast.

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