Static Ignition Concerns in Aboveground Petroleum Storage Tanks Guy R. Colonna, PE NTEPS Ft. Worth, TX January 22, 2009

Overview Hazard Recognition Hazard Recognition –Industry experiences Barton Solvents, Kansas – CSB investigation Barton Solvents, Kansas – CSB investigation –What is static electricity? Hazard Evaluation Hazard Evaluation –Static accumulating liquids Hazard Control Hazard Control –Four steps –API 2003, ISGOTT, NFPA 77

Barton Solvents – Valley Center, KS Date: July 17, 2007 Date: July 17, 2007 Product: VM & P Naphtha Product: VM & P Naphtha Operation: Operation: –Transfer naphtha from tanker truck to 15,000 gallon aboveground storage tank Incident: explosion and fire Incident: explosion and fire –Destroyed tank farm – tank blown 130 ft. –Evacuate 6000 residents

Barton Solvents – Fire

CSB Video _ID=73

Barton Solvents – Explosion

Level Float – showing linkage

Varnish Makers’ & Painters’ (VM & P) Naphtha Properties Flash Point – 58°F (14°C) as tested by CSB Flash Point – 58°F (14°C) as tested by CSB –NFPA Fire Protection Guide to Hazardous Materials lists 28°F, 50°F and 85°F –NFPA 30 Classification – IB (IC) Flammable Range – % Flammable Range – % Conductivity – 3 pS/m (per CSB tests) Conductivity – 3 pS/m (per CSB tests) –Less than 100 pS/m generally considered nonconductive

CSB Key Findings Ignitable vapor-air mixture in head space Ignitable vapor-air mixture in head space Stop-start filling introduced air in the transfer piping agitating sediment and water – bubbling effect Stop-start filling introduced air in the transfer piping agitating sediment and water – bubbling effect Liquid level gauging system float with loose linkage provided gap for potential spark Liquid level gauging system float with loose linkage provided gap for potential spark MSDS for VM&P naphtha inadequate MSDS for VM&P naphtha inadequate

CSB Recommendations – nonconductive flammable liquids Request additional manufacturer guidance Request additional manufacturer guidance Add an inert gas to tank head space Add an inert gas to tank head space Modify or replace loose linkage tank level floats Modify or replace loose linkage tank level floats Add an anti-static agent Add an anti-static agent Reduce flow (pumping) velocity Reduce flow (pumping) velocity –Recommend less than 1 m/sec (Barton was 4.6 m/sec)

CSB Recommendation – request additional manufacturer guidance CSB reported MSDSs do not provide adequate information regarding hazards CSB reported MSDSs do not provide adequate information regarding hazards –Determine whether flammable liquid is nonconductive (static accumulator) –Determine whether flammable liquid is capable of producing ignitable vapor-air mixture inside a storage tank Flash point, vapor pressure, flammable range, minimum ignition energy (MIE) Flash point, vapor pressure, flammable range, minimum ignition energy (MIE)

Liquid Conductivity Non-conductive – static accumulators Non-conductive – static accumulators –Conductivities less than 50 pS/m –Relaxation times greater than 0.36 seconds Semi-conductive – static non-accumulators Semi-conductive – static non-accumulators –Conductivities between 50 pS/m and 10 4 pS/m –Relaxation times between and 0.36 sec Conductive – greater than 10 4 pS/m and less than sec relaxation time Conductive – greater than 10 4 pS/m and less than sec relaxation time

Static Accumulating Liquids VM&P Naphtha VM&P Naphtha Cyclohexane Cyclohexane n-Heptane n-Heptane Benzene Benzene Toluene Toluene n-Hexane n-Hexane Xylene Xylene Ethyl Benzene Ethyl Benzene Styrene Styrene Jet fuels Jet fuels Kerosenes Kerosenes

CSB Recommendation – inert tank head space Eliminate ignitable vapor-air mixture Eliminate ignitable vapor-air mixture –Add nonflammable, nonreactive (inert) gas –Nitrogen, carbon dioxide, argon Consider properties of inert gases Consider properties of inert gases Carbon dioxide as a gas, generates static Carbon dioxide as a gas, generates static –Limiting oxidant concentration (LOC) Refer to NFPA 69 for guidance on values Refer to NFPA 69 for guidance on values –Caution when opening inerted tanks for inspection – oxygen levels will be IDLH

CSB Recommendation – modify tank level float Inert tank head space Inert tank head space Inspect and replace as necessary floats with device that does not cause sparks Inspect and replace as necessary floats with device that does not cause sparks Modify floats – bonded and grounded Modify floats – bonded and grounded Reduce liquid flow velocity Reduce liquid flow velocity Remove slack in the tape connected to the float Remove slack in the tape connected to the float

NFPA 77 - Gauging Where possible, gauging should be carried out using automatic gauging systems Where possible, gauging should be carried out using automatic gauging systems Gauge floats and similar devices should be electrically bonded to the tank shell through a conductive lead-in tape or conductive guide wires Gauge floats and similar devices should be electrically bonded to the tank shell through a conductive lead-in tape or conductive guide wires Free-floating, unbonded floats can be effective spark promoters and should be avoided Free-floating, unbonded floats can be effective spark promoters and should be avoided

Static Electricity Basics Charge must be generated by separation of surfaces Charge must be generated by separation of surfaces Charge must be collected and accumulated Charge must be collected and accumulated Charge discharge Charge discharge –Sufficient charge to jump the gap and produce an incendive spark Flammable concentration within the gap Flammable concentration within the gap

Charge Separation Flow of liquids through pipes or filters Flow of liquids through pipes or filters Settling of a solid or immiscible liquid through a liquid Settling of a solid or immiscible liquid through a liquid Ejection of particles or droplets from a nozzle Ejection of particles or droplets from a nozzle Splashing or agitation of a liquid against a solid surface Splashing or agitation of a liquid against a solid surface Vigorous rubbing together and separation of synthetic polymers Vigorous rubbing together and separation of synthetic polymers

Electrostatic Discharge Conductor to conductor – produces spark Conductor to conductor – produces spark Conductor to non-conductor Conductor to non-conductor –Characterized as corona discharge or brush discharge –Generally not associated with a spark –Generally not incendive

Electrostatic Discharge Dependent upon strength of field between points of discharge (voltage difference) Dependent upon strength of field between points of discharge (voltage difference) Field strength near protrusions – greatest Field strength near protrusions – greatest –Single electrode discharges – rarely incendive Two electrode discharges Two electrode discharges –Sampling device and liquid surface –Ungrounded object floating on surface –Ungrounded equipment suspended in tank

Summary - precautions Eliminate flammable vapor-air mixture Eliminate flammable vapor-air mixture –Ventilate to less than 25% LFL or inert Control transfer flow rate Control transfer flow rate Identify properties of products Identify properties of products Bond or ground sampling or gauging devices – fixed or portable Bond or ground sampling or gauging devices – fixed or portable Allow relaxation time Allow relaxation time Add anti-static agent Add anti-static agent

Any Questions?