A deadly explosion that destroyed at least one house and damaged as many as 40 others Monday afternoon was caused by a “volatile, ignitable liquid,” but the source of that liquid remains a mystery, an investigator with the Ontario Fire Marshal’s Office says.

The blast leveled a home on Brimley Road south of Steeles Avenue East shortly before 4:30 p.m., resulting in the death of 57-year-old Paul Zigomanis.

Crews did discover a severed gas line in the area after the explosion, but it is not known if the leak caused the blast or vice versa.

In total, 17 homes were evacuated and approximately 40 residents have not yet been able to return to many of those properties due to concerns over structural damage.

Structural engineers have been called in to determine if the affected homes are safe, OFM Supervisor of Investigative Services Wayne Romaine told reporters Tuesday.

"Of course, those closest to the blast have really sustained a lot of structural damage," he said.

Investigators have not provided an estimate on damage.

Some residents, Romaine said, may not be able to return to their homes.

"There is a lot of personal belongings that they would like to have that they may not be able to have access to," he added. "We will try our best as we kind of move the investigation forward."

Romaine said it is possible that there could be other victims in the debris, which is about five to six feet deep. He would not say if anyone in the neighbourhood has been reported missing.

The OFM is currently trying to determine whether “migrant gases” could have caused the explosion.

“When we are dealing with an explosion like this, it is not so much the ignition or the ignition sequence because there are so many ignition systems within a residence that could have ignited this. What we are going to try to discern is what was the gas, what was the fuel?” he said. “Is it possible that we have migrant gases that have come through the soil and into the basement that caused this? We are going to go to the senses of individuals. Did you smell anything? Was there any type of odour that was picked up? We are looking for any type of indication as to the type of fuel that might be involved.”

Investigators are currently in the beginning stages of what is expected to be a long and tedious process, but Romaine told reporters on Tuesday that he has noticed that there is “very little fire damage to the debris,” which is an indicator that the fuel did not continue to leak out following the explosion.

As for the cause of the explosion, Romaine said investigators aren’t ruling anything out and refused to comment on whether it may be suspicious.

"We are satisfied that... a gaseous explosion transpired that created this particular event," he said.

“The exact ignition of that fuel may not be determined."

Remember for instant breaking news follow @cp24 on Twitter.