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[viiking]

We have a number of underground solvent tanks which are embedded in sand and notionally earthed via contact with the soil.

During a safety audit by an external party we have been advised that our dipstick (which remains within the tank at all times except when it is in use) must be separately earthed. This has been registered as a serious safety non-conformance. We have a problem with this in that there is a possibility that any fuel or solvent going into our underground tank from a road tanker, may in fact develop a static charge during the flow through the filling pipes. There is an assumption that the fuel will dissipate its charge (its relaxation period) over a few minutes so that the charge in the tank will leak to earth.

However if the dip stick is removed from the tank at any time and re-inserted into the tank,  the dip stick will be at zero potential whereas the tank contents may or may not be at the same potential causing a possible spark when the dipstick is reinserted into the tank.

I have talked to safety representatives from Shell and Manildra (an ethanol supply company) and they agree that none of their underground tanks have earthed dipsticks, nor have they heard of any requirement to do so. I worked in the oil and chemical industry for 25 years and never was advised to earth dip sticks which remained in tanks. Yes we knew what relaxation period was, but there was never any discussion about earthing these dipsticks. In addition I assume that every underground fuel tank dip stick in gas stations is also not earthed. I have also researched various standards including NFPA standards and they are vague on this aspect.

 

I live in Sydney Australia.