Why were they renovating Notre Dame with flame throwers? I've done several renovations and never have used open flame for anything. Except for burning items from the demolition that is. Maybe they burned them in the church?
The story is, the crew doing this are real pros with old, old buildings and did not use flame, electricity, welding, nothing like that.
I'm assuming random illegal cigarette but I must admit that I've gotten more open to the arson argument.