Keep in mind that there will always be propane in the tank until someone (someone else, who knows how to handle the closed container by removing the valve or purging it with nitrogen or carbon dioxide before cutting it) opens it up and fully purges it or vents it “through and through” to atmosphere. Even a nominally “empty” propane tank contains propane, only it’s at atmospheric pressure, meaning “propane at the same pressure as the ambient pressure”. There’s propane in the cylinder, but it hasn’t got enough positive pressure to push out, so that cylinder is still dangerous if anyone attempts to cut it open. People are killed every year by attempting to cut open fuel cylinders and barrels without taking the proper precautions to purge and / or clean them first.