why does the petroleum tankers have a hanging chain on the bottom

Question: why does the petroleum tankers have a hanging chain on the bottom
- Keywords:
  chain,
  petroleum,
  tanker
Asked by abhb266 to Beatrice, Charles, George, Kamal, Patricia on 17 Jan 2017.
- Charles Kamau answered on 17 Jan 2017:
  
  Petroleum is highly flammable – I am sure you’ve seen tankers explode on the news. As the petrol is being transported, there is too much friction with the tank itself which may cause a build up of charges – these charges may start a fire. The chain therefore acts as a transport mechanism for these charges to the ground which is harmless.

Question: why does the petroleum tankers have a hanging chain on the bottom