It showed that the most common causes of wildfires from 1992 to 2020 were mishaps related to vehicles and other equipment. “More than 95% of these are human-ignited fires,” he wrote in an email. “Arson is among the causes, but most human-caused fires are not intentional.” · The prospect of arsonists torching Los Angeles gained traction on social media Thursday when a group of people in Woodland Hills detained a man they suspected of setting a trash fire.