9.1.2(b) Purposes of overflows. Tanks filled by a pumping system may, in addition to vents, be fitted with overflows. Overflows prevent overpressurization of a tank if it is overfilled and also provide for safe discharge or disposal of the overflowing liquid. Overflows may also be fitted to limit the level at which a tank may be filled. Overflows are to be sized based on the capacity of the pump and the size of the filling line. Considerations are to be given to receiving the overflow.
9.1.2(c) Combining vents and overflows. Vents may also act as overflows provided all the requirements applicable to both vents and overflows are complied with.
9.1.2(d) Termination of the outlet ends of vents and overflows. Generally, vents emanating from tanks containing liquids likely to evolve flammable or hazardous vapor are to have their outlets located in the open weather. Depending on the liquid contained in the tank, overflow outlets are to be located such that they either discharge overboard or into designated overflow tanks so as to avoid inadvertent flooding of internal spaces. Outlet ends of vents and overflows, where exposed to the weather, are to be provided with means to prevent sea water from entering the tanks through these openings.
9.1.2(e) Small spaces. Small voids which are not fitted with a permanent means of pumping out bilges, or through which no pressurized piping passes, may be exempted from being fitted with vents.