Urbana and Champaign fire departments responded to an explosion at the Chemistry Annex, 601 S. Mathews Ave., at around 4 p.m. Tuesday.

A student poured hydrochloric acid into a waste container, which already had ammonia waste in it, according to campus spokeswoman Robin Kaler. A tight cap was then put on the waste container before the container exploded.

The building was evacuated as the fire departments cleared fumes from the building, Kaler said. Five people were decontaminated.

An Illini-Alert was sent around 4 p.m. warning people to leave the area, if safe to do so. Shortly after the initial Illini-Alert, a second alert said the spill was isolated to one room.

The scene was clear and it was safe to return to the building at around 6 p.m., according to a third Illini-Alert.