Inspectors with Union Pacific Railroad have confirmed no hazardous materials spilled after a cargo train derailed near Interstate 10 in Tucson during Tuesday's monsoon storms.

An investigation attributed the accident to the bad weather.

"It's a rough estimate right now of about 40 cars that derailed," said Brian Keeley with Northwest Fire District.

"A large fire and police presence came into the scene," he said, and the process was tricky in the rain, taking hours to clear the area. "We had a lot of water running on both sides of the track."

There were no passengers on-board and train operators were far enough ahead of the derailed section to avoid being harmed. It's estimated cleanup will take another day or two.