PORTLAND, Ore. (KOIN) — Authorities are investigating an explosive device that was thrown over the fence at Multnomah County Sheriff’s Deputies at the Justice Center Saturday night in downtown Portland.

Portland Fire and Rescue said they believe the improvised explosive device was something similar to an M1000 firework. “This M1000 type of explosive is extremely dangerous, and is nicknamed a quarter stick, in reference to its similarity to a stick of dynamite,” said PF&R in a statement.

Two deputies reported that they were concussed after the explosion went off near them.

Both fire investigators and sheriff’s detectives are investigating the case. Tips can be left anonymously at 503-823-INFO (4636).