Firefighters' day started with a fire at 7:52 a.m. at 2402 Olive St.
That fire was caused by a dryer malfunction and is unrelated to the suspected arson fires, authorities said.
But together, the five fires led to Tuesday being unlike any other day for his department, Fire Chief Eric Schlotter said.
“These fires took a huge response of resources and manpower to extinguish.
"And I’m extremely proud of the way our firefighters professionally accomplished the job of protecting our city,” he added. “They showed incredible endurance, both physically and mentally, responding to this kind of workload.”