Quick question about making a flamethrower?

I want the fire to be able to burn parts. Should I weld a part to the tool that when touched, it adds a fire to the part, or is there an event for when a particle touches a part?

No, there is not special events for particle emitters or fire objects. You may have to use some form of alternitive.

There is no such a thing for detecting particle but you can use invisible part welded to your tool for detecting area and find the parts using touched or GetTouchingParts I recommend GetTouchingParts because it return touching parts in table so you can filter parts easily