The fire broke out at Lincoln Electric of Canada on Wicksteed Ave., in the Eglinton Ave. E. and Laird Dr. area, just before 3:30 a.m.
After battling the flames for several hours, fire crews were still at the scene at 8:30 a.m., attempting to put out a stubborn spot on the asphalt roof.
“The fire came through the roof. We're spraying water on it right now. The water continues to run off the asphalt,” Kostiuk said.
It will take another few hours before the owners of the plant are allowed back inside to assess the damage, he added.
There were about 20 workers inside the plant when a partition wall caught fire, but all managed to make it out of the building uninjured.
Investigators believe the fire may have been triggered by maintenance work last night on one of the plantÂ’s production lines, Kostiuk said.
“It’s not an arson,” Toronto police Staff Sgt. David Eustace said. “It’s just an accidental fire.”
By 4 a.m., the fire had jumped from a two-alarm level blaze to three-alarm.
Shortly after, it appeared the fire was out, until it started spitting flames again around 4:30 a.m., Eustace said.
At one point, all firefighters had to exit the building as the flames burst through the roof of the large industrial complex, Toronto Fire Capt. Mike Strapko said, adding, “The structural integrity could have been compromised in the roof area.”
At 5:30 a.m., the fire jumped to the fourth alarm level.
After going through a defensive fight with the fire, crews were able to bring it under control and down to the first-alarm level by 7 a.m.
“We had 30 fire units on scene, about 100 firefighters,” Strapko said just after 7 a.m. “Most of them have cleared up."
On its website, Lincoln Electric describes itself as “the world leader in the design, development and manufacture of arc welding products, robotic welding systems, plasma and oxyfuel cutting equipment.”
Surrounding buildings werenÂ’t evacuated and there were no reports of firefighters being injured.
The investigation is continuing and Toronto fire estimates damage to be about $200,000.
This is the second major fire in the last three months on Wicksteed Ave. On Jan. 31, more than 100 firefighters were called to a frozen food storage plant after a fire jumped to five alarms, the highest level.
Residents in the area were advised to keep their windows closed, while motorists reported smoke drifting onto the Don Valley Parkway near Eglinton Ave. E.
Some firefighters were treated at the scene for minor smoke inhalation.