By 4:30 p.m. the 50 firefighters who responded to the fire on the O'Connor House's second floor had contained the blaze, though they still on the scene Thursday morning. Although there were no injuries reported, air quality inside the school's main building was a concern. Custodians were relocated off campus to perform their duties after several reported having headaches, said Baker.

"They came in to test the air quality yesterday," she said, adding the board's facility department found no lingering health threats. "We did a thorough scrubbing of everything and now it's business as usual."

The extent of damage to the building, which was undergoing a $5-million restoration that was near completion, and the cause of the inferno have yet to be determined.

"(There's) a fair bit of damage from smoke and water," said Baker. "It's going to take them a couple of weeks to do the investigation."

The home was built by Senator Frank O’Connor. Upon his death in 1939, the house was handed down to the De La Salle Christian Brothers who with the Daughters of Wisdom founded Senator O’Connor College School on the estate grounds in 1963. O’Connor was not only a generous Catholic philanthropist but also a noted politician and founder of the Laura Secord chocolate company.

The Christian Brothers left O’Connor House in 2000 and sold the buildings to the Toronto Catholic District School Board. The home, unused, began to deteriorate and was threatened with demolition on more than one occasion because of the steep cost of restoration. The house was saved through the efforts of the O'Connor Irish Heritage House, whose board hoped to use the house for promoting culture, heritage, community and learning, Irish and beyond. It had raised most of the funds for the restoration, which included a $2.1-million grant from the federal government in 2010.