The vehicles carrying inflammable fluids usually have metallic chains touching the ground : (1) To conduct excess charge due to air friction to

The vehicles carrying inflammable fluids usually have metallic chains touching the ground : 

(1) To conduct excess charge due to air friction to ground and prevent sparking. 

(2) To alert other vehicles. 

(3) To protect tyres from catching dirt from ground. 

(4) It is a custom.                     (JEE-2024)