Each location where gas cylinders are filled must be pre-approved and known by the government. Each regonized filling terminal has a recognized code. For Seminck Gas the code is: 'ZO'. After filling the bottle, this code must be stamped onto the valve of the cylinder. In other words, each cylinder that you buy should be equipped with a seal bearing the granted filling. The list of approved filling centers and their code is published on the website of the Belgian Ministry of Economic Affairs. This way you always know where the bottle was filled. If happen to buy a dirty, rusted cylinder, you should ask yourself if this is a safe cylinder to use. A clean, properly filled cylinder, fitted with a seal of guarantee is a safely filled cylinder with a correct amount of gas. Check out the website of our own filling station GFS: www.gfs-terminals.be.