Vehicles carrying inflammable materials usually have metallic ropes touching the ground during the motion. why?

vehicles carrying inflammable materials usually have metallic ropes touching the ground during the motion of the vehicle because the body of the vehicle in motion is charged due to air friction.

explanation:

friction causes the vehicle to become charged and can pose a threat. so excess static and friction is let off on the ground by the ropes

it was given as a lesson and guide for prayer.