Crews who were initially sent to investigate a residential fire signal on Avenue K South just before 6:30 p.m. on Sept. 13 said they saw significant black smoke in the area.
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They traced the smoke to a fire at a commercial building in the 200 block of Avenue I South and a second alarm was sounded.
Firefighters softened the fire from the exterior with the intention of continuing to put out the fire from inside the structure, fire officials said.
The commanding battalion chief ordered all firefighters to exit the structure when the fire escalated.
A partial collapse of the building then occurred as the building had been severely compromised, officials said.
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The fire department said the blaze was contained to the structure of origin. They added that firefighters were extinguishing flare-ups and monitoring the fire until around 5 a.m. on Monday.
According to a press release, investigators have identified the cause to be incendiary. The Saskatoon Fire Department defines incendiary as a fire that has been deliberately set.
Damage is estimated at roughly $750,000, fire officials said.
Fire department officials said crews had to deal with arcing power lines, nearby electrical boxes and on-site propane tanks while battling the blaze.
No injuries were reported.