WICHITA, Kan. (AP) — Classes resumed at Wallace Hall on the Wichita State University campus after a mercury spill closed it on Monday.

KWCH reports the air was tested Wednesday morning and crews determined it was safe to reopen the hall, which houses part of the university’s engineering school.

The spill was reported Monday after a scientific instrument broke.

The lab was closed immediately and the spill was confined to that room. The school closed the building and classes were canceled until the spill was cleaned up.