The danger of equalization currents between ships and the loading dock occurs by electrochemical processes, independent of filling.
The ship, the metal construction of the loading dock and the water as electrolyte between them form a galvanic cell .
There is a voltage difference between the electrodes of this cell. Any conductive connection between the electrodes will lead to a undefined flow of electric current .
This current flow can cause hot spots at connection points and generate sparks while disconnecting the inductive elements. These sparks could cause a lethal ignition in hazardous areas.
The effect of a potential difference takes place as soon as the vessel has been moored, and not just during loading and unloading. To avoid such unregulated current flow, different guidelines for tankers and terminals specify to electrically isolate the vessel from shore.
Typically, non-conductive flanges are used to insulate vessels from shore, to account for the physical effect. However, there are still risks that a conductive connection be created by chance (with walkways, with metal ropes or tools). This risk is related to a combination of factors during the total uptime of the terminal and the variety of vessel loading processes.