Spontaneous combustion started Preble fire

Damage inside Green Bay Preble High School is seen Aug. 10, 2014, two days after a fire. (Green Bay Area Public School District photo)

GREEN BAY - Fire investigators say spontaneous combustion ignited the fire in Green Bay Preble High School's gym last week.

They say the fire might have been prevented if district employees had cleaned up correctly after resurfacing the gym's wood floor.

“They placed rags that were used to clean up some of the product that was used to resurface the floor and that product actually spontaneously combusted with those cotton rags, started the plastic garbage can that was placed next to the bleachers on fire,” said Lt. Nick Craig with the Green Bay Metro Fire Department.

Craig says it was all caught on video surveillance.

The school district says it is launching its own investigation to determine whether it should discipline its employees.

“I can guarantee you it wasn't done on purpose,” said Mike Stangel, the district’s facilities director.

University of Wisconsin-Green Bay Chemistry professor Franklin Chen says the rags shouldn't have just been thrown away. He says wood resurfacing products have low ignition points, meaning enough heat will start a fire.

“But in a garbage can or what happened, that heat cannot be dissipated, so that heat accumulated,” said Chen.

“You need to lay them flat, so that chemical can dry completely,” said Craig. “When they're bunched up and balled up and put in a confined container, that's when that spontaneous combustion can happen.”

Lt. Craig says he has seen about 10 fires in his career that started in a similar way. He says one was recent at a home in Allouez.

“About a month ago we had a similar fire in a garbage can with rags that were used in the wood process and then disposed of in a garbage can, so it can happen,” said Craig.

Restoration crews say they should know in the next day or two when students will be able to return.

District officials say school likely will not be able to start on Sept. 2, like originally planned. They say they should know by the end of the week when school will start.