The toroidal tank constitutes the largest and heaviest additional element and is found at the back of the vehicle in place of the spare wheel, securely fixed to the bodywork. It is made of highly resistant steel, thermally treated and tested for up to 30 bar pressures, above the normal working pressure, variable between 2-15 bar. Each tank is submitted to severe checks envisioned by the Land Transport Department. For further safety, the law also prescribes, a filling limit of up to 80% of the total volume. However, by law, the tank must be replaced after 10 years from the date of registration.