The loud, concussive boom that came from an American River College Automotive Collision Repair dumpster next to Raef Hall just before 3 p.m. on Monday, Sept. 17 was likely caused by a large firecracker, according to ARC police.

“We got a call of an explosion in a dumpster,” Sergeant Mike Olson said. “We were told it was an M-80, but we are unsure how someone knows that.”

There was evidence of red-wrapped cardboard in the dumpster, Olson said, which is consistent with an M-80 — a sizable type of firecracker.

Wires were also found inside the dumpster, however Olson said they weren’t believed to be connected to the firework.

“The wires look like old debris from cleaning out a building and was previous garbage,” Olson said.

The explosive sound shocked the campus and was heard from as far as the Liberal Arts building several hundred yards away from the dumpster located next to the women’s bathroom in Raef Hall.

The sound and white smoke cleared out classes nearby until police declared it safe to return.

Dozens of students and onlookers were asked to stay away by faculty members until police arrived.

M-80s are a large class of firecracker, also known as “salutes,” according to the Fireworks Glossary. They were originally made in the early 20th century by the U.S. military to simulate artillery fire during training and are illegal in California.