Cause of Ringneck Ethanol Plant explosion still unknown

ONIDA, S.D. — The ethanol plant explosion that rocked Onida on Sunday afternoon is still under investigation by the South Dakota State Fire Marshal.

Witnesses in the area said they heard and felt an explosion emanate from Ringneck Ethanol Plant on Sunday afternoon.

Onida Volunteer Fire Chief Caleb Shepherd said the investigation into the source and cause of the explosion is ongoing. Nobody was injured in this explosion.

Bill Gibbons, a researcher at South Dakota State University’s Agricultural Experiment Station, said the explosion could have been caused by a variety of different factors. Gibbons said he doubts any actual ethanol caught on fire.

“It’s hard to know if you have an ethanol fire or not because it’s almost invisible to the eye,” Gibbons said.

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In a video and photo of the flame rising from the plant, the flame looked reddish orange, and was spewing upwards as if its source was pressurized.

A potential alternative source of the fire, Gibbons said, is distiller grains.

Distiller grains, and some of the gasses that come off of it during production, do have some low level volatile organic compounds that are byproducts of the fermentation products, Gibbons said.

“When they get concentrated later on – you know, these processes, it can generate compounds that would be flammable,” Gibbons said.

The last ethanol plant explosion occurred in Wood River, Nebraska, in April, when an explosion at a decommissioned plant killed one worker and injured four others. The cause of that explosion was reported as "accidental in nature," and "a result of maintenance work being done on a whole stillage tank."

In its annual report recording nationwide grain dust bin explosions, Purdue University found an increase in the number of grain bin explosions from eight in 2021 to nine in 2022 . These explosions occurred in a number of different types of plants, including one ethanol plant, two feed mills, two grain elevators, two rice mills and two grain processing plants.

One hypothesis Gibbons gave for the cause of the explosion and fire for the Ringneck explosion was grain dust igniting.

During ethanol production, corn grain is ground down to a fine dust to help it get processed more efficiently. If the grain dust is not properly contained during this process, it can accumulate on or in equipment in the plant.

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Corn grain dust is flammable, and ethanol plants create a lot of it. Gibbons likened the flammability of grain dust to a wood log. Holding a match to one, it wouldn’t likely burn, let alone explode.

“But if you ground that log into very, very fine sawdust and put it out in air, or aerosolized it somehow, and introduced a match to that, you’d have an explosion,” Gibbons said.

Most ethanol plants have processes for filtering out the corn dust, Gibbons said. The grinding usually takes place in a small, confined space, with cyclone air handling systems pumping air through it.

A properly outfitted plant would reduce its risk of causing an explosion, Gibbons said, but grain dust can wreak havoc if it is not properly handled. In the nine plant explosions recorded in the Purdue University study, grain dust was identified as the main fuel source for every one.

“All it takes is a small spark for ignition to occur,” said Kingsly Ambrose, an associate professor of agricultural and biological engineering and the author of the report. “Controlling grain dust can significantly reduce the possibility and severity of explosions. Simple and effective housekeeping is the first line of defense.”

Ringneck Ethanol Plant CEO Walter Wendland said that there was no natural gas or ethanol in the building when it exploded.

As of Monday, the State Fire Marshal’s investigation into the determined cause and source of the explosion is inconclusive and ongoing. Stay tuned as this story develops.

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