HARRISON – Harrison Fire Rescue has been working for six days to put out a smoldering fire in a pile of of wood chips at mulching company Skid & Pallet, Inc., at N8924 Lake Park Road.

The fire was caused by spontaneous combustion, fire chief Jarred Gerl said Thursday. Spontaneous combustion can occur when decomposing materials generate enough heat to start a fire without an outside source, and large piles of wood chips or mulch can be a culprit.

The fire department was first dispatched to Skid & Pallet last Friday. Gerl said he hopes the department will finish putting out the fire Thursday night.

“Because it’s such a large pile, it’s taking some heavy equipment and machinery to get into the fire and put it out," Gerl said.

The fire department has been sharing updates and describing the process on its Facebook page.

"Unlike most firefighting operations that cease after putting water on the fire, we are battling spontaneous combustion in large piles of wood chips," a Wednesday Facebook update said. "Firefighters are spraying the piles while a backhoe digs into the pile and turns the debris. Once the chips have been wetted to prevent fire spread, a loader fills waiting dump trucks for removal using an assembly line process. Although effective, it is a tedious process that helps reduce smoke and reignition."

There has been no damage beyond the mulch piles, and no injuries, Gerl said.

Contact Kelli Arseneau at (920) 213-3721 or karseneau@gannett.com. Follow her on Twitter at @ArseneauKelli.