The aircraft was being used to dispense aerial incendiary devices (AIDs) to control forest burning. The AIDs were 1.25 inch diameter polystyrene balls containing potassium permanganate. They were injected with ethylene glycol prior to being dropped out of the aircraft by a dispensing machine. The machine was installed on the cabin floor in front of the right door opening. Fire erupted in an extra supply of AID balls located in the canopy bubble forward of the seats. The extra AIDs were stored in plastic bags. After the fire erupted, the pilot attempted to land on a nearby road, but lost control because of the fire. The crewmember did not jettison the AID dispenser because the fire was in the canopy bubble. The AID balls had been shipped in black plastic bags and packed in corrugated paper cartons. The extra supplies of AIDs in the aircraft were in the plastic bags that had been removed from the corrugated cartons. Operating instructions allowed for extra cartons of AIDs to be carried in the cabin of the aircraft, if they were securely fastened.