Grounding Above-Ground Storage Tanks:

Petroleum liquids are capable of building up electrical charges while they (a) flow by piping, (b) are agitated within a tank or a container, or (c) are subjected to vigorous mechanical movement like as splashing or spraying.  Proper grounding or bonding of the transfer system commonly dissipates this static charge to ground as it is generated.  Therefore, rapid flow rates in transfer lines could cause extremely high electrical potentials on the surface of liquids regardless of vessel grounding. In addition, a few petroleum liquids are poor conductors of electricity, particularly the pure, refined products, and even by the transfer system is properly grounded, a static charge might build up on the surface of the liquid within the receiving container.   A charge accumulates since static electricity cannot flow by the liquid to the grounded metal container as quick as it is being produced. A static spark along with sufficient energy to ignite a flammable air-vapor mixture could occur while the liquid level approaches a grounded probe or while a probe is lowered within a tank for sampling or gaging if this accumulated charge builds up high sufficient.

This high static charge is commonly controlled through decreasing the flow rates, preventing violent splashing along with side-flow fill lines, and by using relaxation time, that permits time for the static charge to discharge.

While flammable liquids are transferred from one container to the other one, a means of bonding should be given among the two conductive containers prior to pouring, as display in Figure.

Within areas where flammable liquids are used or stored, hose nozzles on steam lines used for cleaning should be bonded to the surface of the vessel or object being cleaned.  In addition, there should be no insulated conductive objects on that the steam could impinge and induce a static charge accumulation.

Grounding Above-Ground Storage Tanks