U.S. Navy officials are investigating after a white powdery substance was found in the mailroom of Naval Support Facility (NSF) Arlington.

Initial testing showed that the white powder substance found in an envelope was not poisonous, Navy spokesman Lt. Cmdr. Ryan Perry told CNN’s Barbara Starr.

At the time, 800 people have been evacuated, according to the Navy Times.

The people who were evacuated have not been let back in the building just yet, Lt. Cmdr. Perry said.