We now know what started a fire that sent a Sioux City firefighter to the hospital.
Sparks from a welder caused insulation inside a trailer to catch fire just before four Wednesday afternoon.
Sioux City Fire Rescue responded to the call at Jim Hawk Truck Trailer at 5200 South Lewis Boulevard.
When crews arrived they saw heavy smoke and flames coming from the building.
It took them about 20 minutes to put out the fire.
All 12 people inside the building made it out safely, but one firefighter was transported to Mercy Medical Center for heat exhaustion.
He was released and returned to duty.
The fire caused major damage to the building, and also several trailers inside.