A powdery substance that triggered the evacuation of the Ryerson Library Building on Monday poses no threat, police confirm.

The Emergency Task Force of the Toronto Police has examined the substance and determined the powder is harmless, says spokesperson Const. Tonyo Vella. 

"There was nothing (dangerous) in the package," Vella said Wednesday afternoon, referring to the envelope that contained the powder.

Vella said an investigation is now underway into who slid the envelope into an office in the admissions and enrolment services area on the lower level of the Library Building on Monday morning.

The area -- which has been blocked off since the incident -- will reopen Thursday, says Ryerson spokesperson Bruce Piercey.

The entire building was evacuated shortly after 6:30 a.m. Monday when the envelope, which also included a note, was discovered by a staff member.

There was initially one person in the room, but three others walked in later. In all, four people were briefly quarantined over fears the powder could be anthrax. 

By Monday evening, the upper levels of the Library building had reopened but classes slated to be held in LIB 72 were relocated. As of Thursday, all classes and events scheduled to take place in the building will proceed as usual.