The source of a loud explosion heard throughout town Wednesday is believed to be from an exploding target used for firearms practice.

Washington Fire Chief Bill Halmich said after police and fire crews found no signs of any explosion, the working theory is that the noise came from a Tannerite-type explosive.

Halmich said Tannerite is a target used for firearms practice. When hit with a high-velocity round of ammunition, it explodes.

Emergency crews were inundated with calls Wednesday, Dec. 20, at around 7:15 p.m. for a loud explosion in the eastern end of town near the city’s wastewater treatment plant. Halmich said fire and police canvassed the area to try and locate the source.

Crews located a haze cloud near the treatment plant, but found no issues at the plant.

Washington Water/Wastewater Superintendent Kevin Quaethem said late Wednesday night there was nothing wrong with the treatment plant.

Quaethem said there was not an explosion at the plant. No alarm sounded and no issues were reported from the plant, but crews still inspected the facility to see if the plant was the source of the noise.

Hydrogen sulfide is produced during the treatment process at very low levels at the plant. If the hydrogen sulfide levels reach a certain point, the results would be explosive. That was not the case Wednesday.

Quaethem said all the levels in the plant were normal and everything was operating “correctly and properly.”

Halmich said crews checked other areas of town and found no signs of any explosion. After talking with fire and police officers who heard the noise, he said the working theory was a Tannerite explosion.

Halmich said the theory was backed up when several citizens reported hearing a rifle shot prior to the explosion.

“We’re pretty sure that’s what happened,” he said.

Washington police said it believes the explosion originated outside city limits. Police said they don’t believe any laws were broken because Tannerite is a legal product.

Halmich said Tannerite is not made for populated areas.

“People have got to realize there are serious implications,” he said. “Something like this prompts an emergency response that’s not necessary.”