An explosion at an alternative fuel business Thursday afternoon collapsed an industrial building on Easy Street and left one person dead, authorities said.

Tyson Larson, 28, of Simi Valley, died of multiple blunt force injuries, according to the Ventura County Medical Examiner’s Office.

According to Ventura County Fire Capt. Ron Oatman, on June 17 at about 1:15 p.m., both the Simi Valley police and fire departments received multiple calls of an explosion heard and smoke seen in the 400 block of Easy Street.

Fire trucks and paramedics were dispatched to the scene, as well as all available police units. Upon arrival, the responding personnel did not find a fire but the four-unit industrial building at 480 E. Easy Street was “partially to totally collapsed,” Oatman said.

The business, Realm Industries, experienced a similar incident in December 2008 when a high-pressure tank used to create alternative fuel out of water imploded due to mechanical failure. Larson suffered minor to moderate burn injuries as a result of that explosion.

After that incident, the operation moved from its location at 2320 N. Shasta Way to a nearby industrial unit on Easy Street, directly across from Time Warner Cable.

At the time of Thursday’s explosion, three people were inside the building. Two were found immediately, uninjured, but the third, Larson, was missing, presumed to be inside the building.

The captain said a Simi fire crew made an “aggressive” search of the building and found Larson, who was pronounced dead at the scene.

Following the explosion, authorities didn’t have much information on what caused the blast. Oatman said all they knew was that it was a water-based explosion and that the business operating out of the unit in which the explosion occurred deals in alternative fuels.

Unsure of the cause, firefighters assumed the potential for another explosion and evacuated neighboring businesses within a half-mile radius.

“It was pretty hectic at the beginning,” Oatman said.

Arroyo Elementary School and nearby homeowners were not evacuated because they were not within that radius, the fire captain said.

In addition, Easy Street from First Street to Madera Road was blocked off, causing traffic delays on both sides.

Police and fire are continuing to investigate the incident. A hazardous materials team, bomb squad and SWAT team were on site to assess the situation and even hours after the explosion, authorities were still assuming the risk of another explosion.

Moorpark resident Diane Hedding and her husband, Karl, own Servpro, a fire and flood restoration company, located in a unit in the building that collapsed.

Hedding said she was shaken up by the experience and that the loud explosion literally rattled the businesses in the area.

“I thought a plane crashed into it. Both my husband and I jumped up and the SWAT and emergency people were there immediately,” she said, adding, “The roof of the building was blown off, debris was flying all over the place.”

She said she was glad none of Servpro’s cleaning crews were on site at the time.

Although she said she had met the young man who died, she didn’t know him well.

“I think the only thing that saved my husband and I is that the wall between (the units) is concrete,” she said. “I just feel very badly for the poor guy who lost his life.”