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A May 8 fire that devoured a Box Elder ammunition plant, forcing nearby businesses to evacuate and schools to cancel outdoor activities, has been ruled an accident.

The blaze at Ultramax Ammunition originated from work being done on the building’s heating, ventilation and air-conditioning system, according to the Bureau of Alcohol, Tobacco, Firearms and Explosives.

It was caused by either "welding or soldering," Kurt Wheeler, supervisor of the ATF in South Dakota, said in an interview Monday. "Someone saw the fire start."

Since the incident didn't involve a criminal act, the ATF has finished its part in the case, Wheeler said. The ATF took the lead in the investigation, which included the state fire marshal, because Ultramax is a federally licensed ammunition manufacturer.

The state fire marshal, which is still looking into the incident, found that the fire appeared to be "accidental in nature," Department of Public Safety spokesman Tony Mangan said. 

Both the ATF and the state fire marshal couldn’t give a cost for the fire damage.

When firefighters arrived at the scene that Tuesday morning, heavy smoke and flames were already coming out of the plant on Elk Vale Road. Firefighters had to pull back about half a mile from the building after bullets stored inside began exploding. Authorities said the plant had been filed with millions of rounds and gun powder.

Neighboring businesses, such as the Flying J truck stop, were evacuated and several roads were closed. Rapid Valley Elementary, Valley View Elementary and East Middle School, located nearby, were placed on secure status for three hours to prevent students from going outdoors and being exposed to hazardous smoke.

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Around a dozen agencies responded, including the fire departments of Box Elder, Ellsworth Air Force Base, North Haines, Rapid City and Rapid Valley. Firefighters declared the plant building a total loss.

The following Monday, Ultramax resumed part of its operations — including manufacturing activities — from a “back building,” said a company representative who didn’t want to be identified. “So we didn’t have a hundred percent loss,” the person said.

The plant will be rebuilt on the same site, and the new facility is expected to be ready by the end of the year. The company declined to comment on the fire investigation.

Ultramax, founded in 1986, is one of six ammunition manufacturers based in the Rapid City Area, according to the ATF. There are 16 throughout South Dakota.

Contact Tiffany Tan at

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Cops and Courts Reporter

Cops and courts reporter for the Rapid City Journal