GREEN BAY, WI- Investigators say a spontaneous combustion of chemicals on cotton rags started the blaze at Green Bay's Preble High School.
"Was something done wrong, were they improperly disposed of? Yes they were improperly disposed of. Did they do it on purpose? obviously not," says Lt. Nick Craig with the Green Bay Fire Department.
That means a possible late start to the school year for more than two thousand students.
"We'll have to make up the time that is lost, instructional time for the school year," says Principal Natasha Rowell.
Clean up crews have a large task ahead of them tonight.
It's extensive smoke damage at Preble High School that's forcing the school to open later than September 2nd.
So restoration crews working around the clock to get students back in school.
More than one hundred workers increasing to four hundred come Wednesday.
"We've got to address every room, every closet, every cavity in the building one way or another," says J. Murphy with Paul Davis National.
School leaders have not ruled out students attending class at other schools. They will release more info later this week. Restoration crews say the school will be open at some point in September no exact date yet.