Debasis The generation of static electricity in petroleum storage tanks cannot be prevented absolutely but may be minimized or eliminated by taking precuations through certain procedures. Though it is difficult to answer all paoints raised, i would suggest you to go through the following - if you have access for these publications or you can purchase for your reference and application in your plant. ISGOTT- International Safety Guide for Oil Tankers and Terminals and the May 1991 addendum extending anti-static precautions to residual fuel oils and other oils. API 2003- API Recommended Practice 2003, 'Protection Against Ignitions Arising out of Static, Lightning, and Stray Currents". API 2015- API Publication 2015, "Safe Entry and Cleaning of Petroleum Tanks". NFPA 77- "Static Electricity Sun- Sun Oil Co. Safety Manual. Texaco- Texaco Inc. Research, Environment and Safety Department, "Static Electricity Code". Loading Precautions The following are essential only when loading static accumulator oils (conductivity < 50 pS/m): Restrict initial loading rates, when splashing and surface turbulence occur, to flow rates less than 1 meter/second (volume flow rate conversions available). Adequate inlet coverage's are: side or horizontal entrance- 0.6 meter; downward pointing inlet- twice the inlet diameter. ISGOTT %B7 Loading rate conversions appear both in ISGOTT and Texaco. %B7 Restrict initial unloading rates to shore installations also, as long as inlets in the shore tank are not covered with liquid. The inlet fill pipe should discharge near the bottom of the tank. NFPA 77 %B7 Keep water and other impurities out of the incoming cargo stream as much as possible. Extra care with loading and unloading rates when presence of impurities (e.g., water, sulfur, metals) is suspected is essential. ISGOTT, NFPA 77 %B7 Avoid pumping entrained gases with cargo. NFPA 77 %B7 Degassing (to <20% of LFL at tank bottom) or inerting a ship's tank eliminates loading rate restrictions due to static electricity. Texaco %B7 Reduced pumping speeds are used for discharge of slops and other "mixed-phase flow" (some ballast) to shore tanks. Prevention of charge accumulation - recommended by ISGOTT /NFPA 77 The following safety precautions have been developed to prevent the accumulation of static charge. Antistatic additives These additives raise the conductivity of a static accumulator; one specification calls for a minimum of 100 pS/m. ISGOTT Treatment is required for these fuels in Canada. The Canadian General Standards Board specifies minimum conductivity of 50 pS/m for static accumulating fuels, especially aviation fuels . Iam not sure of the Indian Refinery standards for this. May be OISD has a specific standard to address this treatment of additives for anti static electric discharge. API 2003 recommends that these additives be introduced at the beginning of the "distribution train", and notes that their positive effect may be reduced by repeated shipments or passage through clay filters. Safety precautions for the handling of static accumulating oils have historically been waived for those treated with antistatic additives. These precautions have, however, recently been extended to residual oils and oils treated with anti-static additive to raise conductivity above 50 pS/m (May 1991 amendment to ISGOTT). The document is silent as to treated oils at or above 100 pS/m. Relaxation of static accumulators The charge which accumulates in a poorly conducting liquid will slowly dissipate after loading is completed and the cargo is still. Relaxation time of 30 minutes is recommended after loading of static accumulating oils before introduction of cargo sensors into the tank. ISGOTT Texaco specifies a 15 minute relaxation World voer there have been several catastrophic accidents due to static electric discharge in petroleum storage tanks. Space is too small to give full details. You can get ample literature / case histories of such accidents from published journals and published symposium. Basically, this problem can be a great extent mitigarted if : A firm earthing connection exists between tank top to bottom on all sides (four quandrantss), measurement of earthing measuremens once in 6 months to meet both Indian Electricity regulations, as well Indian Petrolem and over all for API construction code requirements, firm earthing at all jump-over points(especially piping joints in and out of tanks). Allowing enough settling time betwenn tank loading and allow time for tank discharge (i.e, withdrawal of naphtha), good lightning arrestor at the top of the tanks and the continuity of the same will help you to avoid major catastrophy in naphtha storage tanks - inspie of unpreventable static electric discharge. As a precaution, do not load the tank too fast or take fuel discharge during severe lightning time. Trust this is of help to you C.V.Srinivasan Nishi Engineers Pvt Ltd India August 15, 2005 E-mail: nishi@vsnl.com >I need views and opinion from the expert forum here. > >It is being said that static electricity charge gets >build-up in hydrocarbon (HC) liquids during transfer >operations like "sending HC from a hose/nozzle" ; "movement >of liquid in a pipe" ; "during mixing , pouring, agitation , >splashing of liquids". And this charge can get carried into >downstream of the tank. The accident potential increases >with increase in build-up charges under LOW CONDUCTIVITY HC >FLUIDS like Naptha , gasoline Blends etc. > >It is also being discussed that Non-Conductive Coatings >inside the tank shell could lead to local static electricity >build-up and can cause potential for fire accident. > >Q1. W.r.t. the above is it required to paint the inside >surface of the tank by some Conductive Coatings which has >static charge dissipation formula? > >Q2. From practical operating experiences anyone has such >experience of fire incidence or has experience of such type >of conductive coating application? > >Please share your views etc. >regards