At approximately 3:25 PM on May 22, 2018, the Central Dakota Communications Center received a report of a fire at a commercial building under construction on the 1700 block of Burnt Boat Loop. The Bismarck Fire Department was dispatched to investigate. The first arriving fire crew reported a three story commercial building with nothing showing from the exterior. The fire crew established command and went to investigate. The fire crew found that construction work was being carried out on the exterior of the building close to the roofline. Welding work had ignited materials inside of a wall. Construction workers used a fire extinguisher in an attempt to extinguish the fire. Fire crews laddered the exterior of the building to search for fire extension within the wall. Additional fire crews arrived on scene and were assigned to search for fire extension to the interior of the building. A small amount of smoldering insulation was found and removed from the exterior wall and no evidence of fire or heat was found inside the building. An overhaul operation was conducted to search for any additional smoldering materials. Five fire department apparatus and nine firefighters were dispatched to the scene. Bismarck Police Department assisted with scene control. Metro Area Ambulance was on scene to provide assistance. There were no injuries to building occupants or firefighters. The fire was caused by welding sparks which ignited insulation materials within the exterior wall. The cause of this fire has been determined to be accidental.