As many as 90 percent of wildland fires in the United States are caused by humans, according to the U.S. Department of Interior. Some human-caused fires result from campfires left unattended, the burning of debris, negligently discarded cigarettes and intentional acts of arson. The remaining 10 percent are started by lightning or lava. Over the 20-year period, 1993 to 2012, fires, including wildfires, accounted for 1.7 percent of insured catastrophes losses, totaling about $6.5 billion, according to the Property Claims Services (PCS) unit of ISO.