Go into a forge game and spawn a propane tank and set it on fixed or the other thing. Also set it in the air upside down then stand on it.

Shoot it until it lights on fire (use a single shot weapon other than the sniper so you dont blow it up).

After it lights on fire immediaetly go into forge and grab it, then touch people with the fire and it will hurt them.

This may take a few trys because it might blow you up before you grab it.