Agree with comments from TRRao. We can not measure the static charge directly but can use indirect measurements using static charge meters which measures the surface potential in kV. We recently used a Surface DC voltmeter and obtained the potential in kV. It was supplied by Alpha labs Inc., USA. You may wish to contact them.
We had three static related flash fires while loading trucks with Xylene, all three happened in summer and in one gantry only. It made us to check the gantry earthing system thouroughly and found that the bonding reel did not make contact with the bonding drum occassionally. The tanker purging with Nitrogen was not adequate leaving a flammbale atm inside the tanker. The product pumping rate was at 2 m/sec linear velocity only. The truck earthing lug was found corroded hence did not make a contact with grounding system of the gantry ocassionally, depending on how one fixes the grounding clip. So of the four steps needed for a static charge to ignite a vapor, we had three steps established through measurement/tests. The only questionw as where from the spark jumped. The loading lance/pipe was of SS and was touching the tanker bottom and the lance was bonded with the gantry structure. The structure was earthed at four earth pits. The Er values were perfect < 10 Ohms.
Still there was an igntion inside the tanker which now we think was caused by a spark gap between the liquid and the lance surface or between the manhole and the lance.
Q. Is it possible for a spark to jump between the lance and liquid surface though the lance is surround / submerged in the liquid?
Q. If the spark is assumed to occur on the top of the tanker between the tanker manhole and the lance, where was the flammable vapour at the manhole cover. Our readings show the LEL was less than 2% on the top during a simulated drill. The charing pattern on the lance indicated that the fire started at the botom and spread to the top.
Can some one advise me on where could have been the spark gap and between what?
Static charge measurement
Re: Static charge measurement
