Here is a handy module that lets you turn your drone into a remotely operated flamethrower. The TF-19 WASP flamethrower drone module has a range of 25ft and 1-gallon fuel capacity. It can shoot a stream of fire for 100 seconds.
This flamethrower module is compatible with drone platforms that can handle payloads 5lbs and over (e.g. DJI S1000).