Static - grounding

[scorer]

At work we insert an earthed grounding rod - in through the top of a plastic IBC (1 tonne plastic contaiber) when filling flammable materials through the top.
Why is this done, and what is the benefit? It seems to me that it is the liquid itself that is being grounded to prevent a spark jumping from the liquid surface to an earthed piece of equipment. Is this correct, and is it normal practice?

 

[25362]

Trevor A. Kletzin his Critical Aspects Of Safety And Loss Prevention ays I quote:

"...contrary to to widesopread belief, earthing does not always prevent static sparks. Suppose a liquid is flowing into a tank:

1. If the tank is not earthed it will become charged and a spark may pass between the tank and earth, igniting any vapour present outside the tank.

2. If the tank is earthed and the liquid is conducting, all the charges on the tank and the liquid will flow to earth and there will be no spark.

3. If the tank is earthed and the liquid is non-conducting then the charge of the tank will drain away to earth but a charge will remain on the liquid. A spark may pass beteen the liquid surface and the tank roof or wall, igniting the vapour present in the vapour space of the tank.

As for methods to prevent the formation of static he and others list several procedures that were already discussed at least in the following

thread378-91957
thread378-92551
thread248-92706

good luck.

 

[scorer]

25362

Thanks for the references. They are an excellent read.