Weber State University police cleared the already all-but-empty Engineering Technology Building on Thursday afternoon when an unknown powder was found on a desk.
WSU spokeswoman Allison Hess said the Ogden City Metro Hazmat Unit was testing the "white, powdery substance" spotted in the second-floor classroom about 12:30 p.m. It eventually turned out to be a non-toxic plaster.
No injuries were reported. About 20 staff and students were evacuated pending results of the testing.