9.5.5 Overflows from Combustible and Flammable Liquid Tanks
Tanks containing combustible and flammable liquids are not to be fitted with overflows discharging overboard. Overflow pipes from these tanks are to be led to an overflow tank or to a storage tank with sufficient excess capacity (normally 10 minutes at transfer pump capacity) to accommodate the overflow. The overflow tank is to be provided with a high level alarm, see 4-6-4/13.5.4. If a sight flow glass is also provided in the overflow pipe, then such sight glasses are to be fitted only in vertical sections of overflow pipes and be in readily visible positions.
9.5.6 Overflow Pipe Wall Thickness
In general, overflow pipes exposed to the weather are to have wall thicknesses not less than standard thickness, see 4-6-4/9.3.2(a). Overflow pipes not exposed to the weather are to meet the thickness requirements of vents in 4-6-4/9.3.2(b). However, that portion of the overflow pipe subject to the provisions of 4-6-4/3.3, as indicated in 4-6-4/9.5.3, are to be in accordance with the pipe wall thicknesses in 4-6-4/3.3