Explanation:
The reason is very simple, when the tanker truck carrying gasoline or oil moves, these substances often come into contact with the dry air inside the tank. On the other hand, this air area rubs against the tank wall, so it is very easy to get electrified.

Combining these two conditions will easily cause fire and explosion due to static electricity, which is a common phenomenon in life when there is an imbalance of electric charges on the surface of a material.

These charges will be retained on that surface until they can be transferred to another place through electric transmission or even discharge with electric sparks that we can observe with the naked eye.

Therefore, using a chain (with a high conductivity coefficient) will help solve the problem of static electricity by quickly converting these 'static' charges into electric current and transmitting them to the ground through the conductor, which is the chain, to neutralize the electricity, thereby avoiding fire and explosion.

Not only is there a risk of static electricity when moving, people also have to deal with this problem when filling the tank with gasoline or vice versa. There are specialized devices such as the RTR – Road Tanker Grounding (Earthing) system used to neutralize electricity.a