Precautions before using an old pressure vessel or fuel container
Extreme caution must be exercised when first cutting open, drilling, or welding any container that has held flammable gas or liquid.
Always fill the vessel to the absolute brim with water before you commence working on it. Any container that has previously held fuel or flammable liquid of any sort, even if it is now clean and empty, will become a bomb once heat or sparks are present. Never cut, weld, or drill into such a container if there is still a pocket of air in it. Remember that any container becomes a potential bomb if even a small residue of flammable vapours catch alight and are confined within it.
If you are uncertain of the previous uses the container has been put to, assume it has had flammable liquid or gas in it and treat it accordingly. This warning should be heeded for any and all containers that may have held flammable liquids or gases in them previously. There are no second chances!