Yes you need to do some things safely otherwise you'll get blown up or burnt ,I would use water for car petrol tanks but with LPG I just use compressed air to fill the tank then let the air out and keep repeating the process until the air coming out of the tank will not burn , it takes quite a few times filling them with air but is less messy, then I cut the tank up.
I've always thought about trying arc cutting rods but no idea how long or how well they work.
