Hundreds arrested over French wildfires, but who is to blame?

Once a fire is out, Eric's first task is to map its outline along the edge of the burnt vegetation, then trace it back to its point of origin. If the wind has been steady, that outline often forms a "V" shape. From there, his team works backwards along the path the flames took."If someone deliberately starts a fire, they may not have used only one device," he says. It improves the chances of a DNA or fingerprint sample being found.Experts believe arson accounts for only a small fraction of fires. Most are believed to be accidental, with sparks potentially coming from construction work, faulty electrical equipment, cigarette butts and barbecues."With cigarettes, it's called the '30' rule," says Eric Dufayet. To start a fire, he explains, there must be "a temperature of at least 30C (86F), a maximum of 30% humidity, wind of less than 30km/h (19mph), and at least 30% of the cigarette unburnt."In the current drought, he says it is even easier. If those conditions are met, a fire can easily spread, and fast.ReutersFrench President Emmanuel Macron called the fires "completely unprecedented"According to Michel Lejoyeux, a professor of psychiatry and addictive behaviour at Paris 7 University, people who start fires fall into three categories: those who are careless, those who benefit - with an insurance payout, for example - and pyromaniacs."The pyromaniac doesn't get money, has no spirit of revenge, has no utility of the fire, but he likes the fire," he says.