# Storage Tank Explosion and Fire - **operation:** document - **citation:** DCA03MP001 - **title:** Storage Tank Explosion and Fire - **source type:** incident - **agency:** National Transportation Safety Board - **status:** current - **official:** true - **published on:** 2026-01-30 - **effective on:** 2003-04-07 - **summary:** Accident. in Glenpool, OK, USA. on 2003-04-07. Other - **machine formats:** - **json:** https://regulus.evalyn.ai/document/ntsb-case-dca03mp001.json - **markdown:** https://regulus.evalyn.ai/document/ntsb-case-dca03mp001.md - **app url:** https://regulus.evalyn.ai/document/ntsb-case-dca03mp001 - **source url:** https://www.ntsb.gov/investigations/Pages/DCA03MP001.aspx **body:** NTSB investigation DCA03MP001. Event Type: Accident Event Date: 2003-04-07 Event City: Glenpool Event State Or Region: OK Event Country: USA Accident Type: Other Completion Status: Completed Report Number: PAR-04-02 Probable cause: The National Transportation Safety Board determines that the probable cause of the April 7, 2003, storage tank explosion and fire in Glenpool, Oklahoma, was ignition of a flammable fuel-air mixture within the tank by a static electricity discharge due to the improper manner in which ConocoPhillips Company conducted tank operations. Contributing to the extent of the property damage and the magnitude of the impact on the local community was the failure of American Electric Power employees to recognize the risk the tank fire posed to the nearby power lines and take effective emergency action. Tier1Name: Post-release Tier2Name: Fire Tier1Name: Other Tier2Name: Explosion Finding Tier1Name: Organizational Finding Tier2Name: Support/oversight/monitoring Finding Tier3Name: Oversight Finding Modifier Name: Federal agency Finding Report Text: Organizational - Support/oversight/monitoring - Oversight - Federal agency Finding Tier1Name: Organizational Finding Tier2Name: Development Finding Tier3Name: (general) Finding Modifier Name: Other institution/organization Finding Report Text: Organizational - Development - (general) - Other institution/organization Finding Tier1Name: Personnel Finding Tier2Name: Action/decision Finding Tier3Name: Information processing/decision making Finding Modifier Name: Other company personnel Finding Report Text: Personnel - Action/decision - Information processing/decision making - Other company personnel Finding Tier1Name: Pipeline Finding Tier2Name: Miscellaneous equipment Finding Tier3Name: Liquid/gas product Finding Modifier Name: Incorrect use/operation Finding Report Text: Pipeline - Miscellaneous equipment - Liquid/gas product - Incorrect use/operation Finding Tier1Name: Environment/Infrastructure Finding Tier2Name: Operating environment/control system Finding Tier3Name: Product control system Finding Modifier Name: Effect on equipment Finding Report Text: Environment/Infrastructure - Operating environment/control system - Product control system - Effect on equipment Official NTSB investigation data. NTSB findings determine probable cause and make safety recommendations; they do not adjudicate civil liability or regulatory violations. What Happened On April 7, 2003, at about 8:55 p.m., central daylight time, an 80,000-barrel storage tank at ConocoPhillips Company’s Glenpool South tank farm in Glenpool, Oklahoma, exploded and burned as it was being filled with diesel. The tank, designated tank 11, had previously contained gasoline, which had been removed from the tank earlier in the day. The tank contained between 7,397 and 7,600 barrels of diesel at the time of the explosion. The resulting fire burned for about 21 hours and damaged two other storage tanks in the area. The cost of the accident, including emergency response, environmental remediation, evacuation, lost product, property damage, and claims, was $2,357,483. There were no injuries or fatalities. Nearby residents were evacuated, and schools were closed for 2 days. What We Found We determined that the probable cause of the April 7, 2003, storage tank explosion and fire in Glenpool, Oklahoma, was ignition of a flammable fuel-air mixture within the tank by a static electricity discharge due to the improper manner in which ConocoPhillips Company conducted tank operations. Contributing to the extent of the property damage and the magnitude of the impact on the local community was the failure of American Electric Power employees to recognize the risk the tank fire posed to the nearby power lines and take effective emergency action. The safety issues identified during the investigation of this accident are as follows: Tank operations, including switch loading, at the ConocoPhillips tank farm. The adequacy of emergency planning and emergency response by ConocoPhillips Company and American Electric Power. The adequacy of Federal regulations and industry standards for emergency planning. What We Recommended As a result of this investigation, we made the following new safety recommendations. To the Research and Special Programs Administration: Revise the emergency response planning requirements in the pipeline safety regulations to include coordination with electric and other utilities that may need to respond to a pipeline emergency. (P-04-07) Issue an advisory bulletin to liquid pipeline operators to validate the accuracy of their tank strapping tables. (P-04-08) To ConocoPhillips Company: Revise your storage tank operating procedures to include instructions for minimizing the possibility of creating a flammable atmosphere and the occurrence of a static discharge inside a tank after a floating roof has been either intentionally or unintentionally landed, especially for tanks where switch loading is likely to occur. (P-04-09) Evaluate your storage tank operating procedures and make the revisions necessary to ensure that product flow rates in both the tank fill line and the discharge nozzles are restricted to provide a level of protection against excess static electricity that is at least commensurate with industry standards. (P-04-10) Revise your emergency response plan for the Glenpool South tank farm area and similar locations where ConocoPhillips Company facilities are near electric utilities to include preplanning with nearby electric facilities. (P-04-11) To American Electric Power: Revise your emergency response plan to include areas, such as the ConocoPhillips Company Glenpool South tank farm, where pipeline transportation facilities are near American Electric Power facilities, and include a requirement that the American Electric Power emergency responders communicate and coordinate with the on-scene agency in charge. (P-04-12) To the Institute of Electrical and Electronics Engineers: Revise the National Electrical Safety Code to establish requirements for operators to prepare and implement emergency response plans for electric facilities where an emergency may affect pipeline facilities or that may be affected by emergencies at pipeline facilities. (P-04-13) To the American Society of Mechanical Engineers: Revise the emergency response planning requirements in your gas and hazardous liquid pipeline codes to include coordination with electric and other utilities that may need to respond to a pipeline emergency. (P-04-14) PAR-04-02 <<>> Storage Tank Explosion and Fire in Glenpool, Oklahoma April 7, 2003 Pipeline Accident Report NTSB/PAR-04/02 PB2004-916502 Notation 7666 National Transportation Safety Board Washington, D.C. <<>> this page intentionally left blank <<>> Pipeline Accident Report Storage Tank Explosion and Fire in Glenpool, Oklahoma April 7, 2003 NTSB/PAR-04/02 PB2004-916502 National Transportation Safety Board Notation 7666 490 L’Enfant Plaza, S.W. Adopted October 13, 2004 Washington, D.C. 20594 <<>> National Transportation Safety Board. 2004. Storage Tank Explosion and Fire in Glenpool, Oklahoma, April 7, 2003. Pipeline Accident Report NTSB/PAR-04/02. Washington, DC. Abstract: About 8:55 p.m., central daylight time, on April 7, 2003, an 80,000-barrel storage tank at ConocoPhillips Company’s Glenpool South tank farm in Glenpool, Oklahoma, exploded and burned as it was being filled with diesel. Gasoline had been removed from the tank earlier in the day. The resulting fire burned for about 21 hours and damaged two other storage tanks in the area. The cost of the accident was $2,357,483. There were no injuries or fatalities. Nearby residents were evacuated, and schools were closed for 2 days. The safety issues identified in this accident are tank operations, including switch loading, at the ConocoPhillips Company tank farm; the adequacy of emergency planning and emergency response by ConocoPhillips and American Electric Power; and the adequacy of Federal regulations and industry standards for emergency planning. As a result of its investigation of this accident, the Safety Board makes safety recommendations to the Research and Special Programs Administration, ConocoPhillips Company, American Electric Power, the American Society of Mechanical Engineers, and the Institute of Electrical and Electronics Engineers. The National Transportation Safety Board is an independent Federal agency dedicated to promoting aviation, railroad, highway, marine, pipeline, and hazardous materials safety. Established in 1967, the agency is mandated by Congress through the Independent Safety Board Act of 1974 to investigate transportation accidents, determine the probable causes of the accidents, issue safety recommendations, study transportation safety issues, and evaluate the safety effectiveness of government agencies involved in transportation. The Safety Board makes public its actions and decisions through accident reports, safety studies, special investigation reports, safety recommendations, and statistical reviews. Recent publications are available in their entirety on the Web at . Other information about available publications also may be obtained from the Web site or by contacting: National Transportation Safety Board Public Inquiries Section, RE-51 490 L’Enfant Plaza, S.W. Washington, D.C. 20594 (800) 877-6799 or (202) 314-6551 Safety Board publications may be purchased, by individual copy or by subscription, from the National Technical Information Service. To purchase this publication, order report number PB2004-916502 from: National Technical Information Service 5285 Port Royal Road Springfield, Virginia 22161 (800) 553-6847 or (703) 605-6000 The Independent Safety Board Act, as codified at 49 U.S.C. Section 1154(b), precludes the admission into evidence or use of Board reports related to an incident or accident in a civil action for damages resulting from a matter mentioned in the report. <<>> iii Pipeline Accident Report Contents Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v Factual Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Accident Synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Accident Narrative . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Emergency Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Meteorological Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 ConocoPhillips Glenpool Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Tank 11 and Appurtenances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Tank Farm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Control Centers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Explorer Glenpool Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 American Electric Power Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Postaccident Field Inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Tank 11 Wreckage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 ConocoPhillips Crude Oil Pipeline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 AEP Power Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 ConocoPhillips Electrical Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Tests and Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Safety Board Materials Laboratory Examination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Diesel Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Design Criteria for Tank Fill Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Switch Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Switch Loading and Tank 11 Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Safety Board Vapor Concentration Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 ConocoPhillips Crude Oil Pipeline Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Operating Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Explorer Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Industry Recommended Tank Filling Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 ConocoPhillips Tank Filling Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Postaccident Actions at ConocoPhillips Glenpool South Tank Farm . . . . . . . . . . . . . . . . . 25 Federal Safety Regulations – Emergency Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Industry Emergency Response Plan Guidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 ConocoPhillips Emergency Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Federal Safety Regulations – Ignition Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Tank Inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Office of Pipeline Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 ConocoPhillips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 National Electrical Safety Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Exclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Static Electricity and Prevention of Accidental Ignition at Storage Tanks . . . . . . . . . . . . . 30 Static Charge Generation, Accumulation, and Dissipation . . . . . . . . . . . . . . . . . . . . . . 30 Floating Roof Position and Spark Gap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 <<>> Contents iv Pipeline Accident Report Accident Switch Loading and Flammable Vapors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Emergency Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 American Electric Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 ConocoPhillips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Emergency Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Federal Oversight of Pipeline Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Probable Cause . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Appendix A: Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 <<>> v Pipeline Accident Report Executive Summary On April 7, 2003, at about 8:55 p.m., central daylight time, an 80,000-barrel storage tank at ConocoPhillips Company’s Glenpool South tank farm in Glenpool, Oklahoma, exploded and burned as it was being filled with diesel. The tank, designated tank 11, had previously contained gasoline, which had been removed from the tank earlier in the day. The tank contained between 7,397 and 7,600 barrels of diesel at the time of the explosion. The resulting fire burned for about 21 hours and damaged two other storage tanks in the area. The cost of the accident, including emergency response, environmental remediation, evacuation, lost product, property damage, and claims, was $2,357,483. There were no injuries or fatalities. Nearby residents were evacuated, and schools were closed for 2 days. The National Transportation Safety Board determines that the probable cause of the April 7, 2003, storage tank explosion and fire in Glenpool, Oklahoma, was ignition of a flammable fuel-air mixture within the tank by a static electricity discharge due to the improper manner in which ConocoPhillips Company conducted tank operations. Contributing to the extent of the property damage and the magnitude of the impact on the local community was the failure of American Electric Power employees to recognize the risk the tank fire posed to the nearby power lines and take effective emergency action. The safety issues identified during the investigation of this accident are as follows: • Tank operations, including switch loading, at the ConocoPhillips tank farm. • The adequacy of emergency planning and emergency response by ConocoPhillips Company and American Electric Power. • The adequacy of Federal regulations and industry standards for emergency planning. As a result of its investigation of this accident, the National Transportation Safety Board makes safety recommendations to the Research and Special Programs Administration, ConocoPhillips Company, American Electric Power, the American Society of Mechanical Engineers, and the Institute of Electrical and Electronics Engineers. <<>> this page intentionally left blank <<>> 1 Pipeline Accident Report Factual Information Accident Synopsis On April 7, 2003, at about 8:55 p.m., central daylight time,1 an 80,000-barrel storage tank at ConocoPhillips Company’s (ConocoPhillips) Glenpool South tank farm in Glenpool, Oklahoma, exploded and burned as it was being filled with diesel. The tank, designated tank 11, had previously contained gasoline, which had been removed from the tank earlier in the day. The tank contained between 7,397 and 7,600 barrels of diesel at the time of the explosion. The resulting fire burned for about 21 hours and damaged two other storage tanks in the area. The cost of the accident, including emergency response, environmental remediation, evacuation, lost product, property damage, and claims, was $2,357,483. There were no injuries or fatalities. Nearby residents were evacuated, and schools were closed for 2 days. Accident Narrative Tank 11 contained about 8,710 barrels2 of gasoline on the afternoon of the accident. The ConocoPhillips operator who was on duty at the time of the accident stated that when she reported for work at Glenpool Terminal at about 3:30 p.m.3 on April 7, 2003, a transfer of gasoline from tank 11 at Glenpool South tank farm, a nearby ConocoPhillips facility, to tankage at Glenpool Terminal, was in progress. Explorer Pipeline Company (Explorer) was scheduled to deliver a batch of diesel into tank 11 about 8:30 p.m., and before that time, the operator would need to complete the transfer of gasoline to Glenpool Terminal and remove the gasoline that remained in the manifold piping and the piping to tank 11. The gasoline from the piping would be transferred to tank 12 at Glenpool South tank farm.4 1 Unless otherwise specified, the times used in this report are central daylight time. 2 A barrel is a liquid measure that, for petroleum, is equal to 42 U.S. gallons. 3 Times in this section are from interviews with ConocoPhillips, Explorer Pipeline Company, and American Electric Power personnel, ConocoPhillips and Explorer Pipeline computer data, the Glenpool fire captain’s summary report, the Glenpool police daily radio log, ConocoPhillips incident tracking notification data, and the Explorer Pipeline Company batch end report. 4 The diesel delivery normally would have been to tank 8, but because of scheduling considerations, the naphtha in tank 8 had not been shipped, making it necessary to empty tank 11 in preparation for the scheduled diesel delivery. In 2002 and 2003, tank 11 was used to store naphtha, toluene, gasoline, and diesel. Naphtha is a petroleum distillate used as a paint solvent, cleaning fluid, and blendstock in gasoline production. Toluene is a petroleum distillate used as an octane booster in fuel and as a solvent in paints and paint thinners, rubber, printing, adhesives, cosmetics, fingernail polish, lacquers, leather tanning, disinfectants, and perfumes. <<>> Factual Information 2 Pipeline Accident Report The piping system at the Glenpool South tank farm allowed products to be delivered to and received from Explorer’s facility, which was northwest of and adjacent to the ConocoPhillips tank farm. (See figure 1.) The piping system also allowed products to be delivered to and received from the ConocoPhillips Glenpool Terminal (also identified by ConocoPhillips as Glenpool Station), which was about 2.7 miles northeast of the Glenpool South tank farm, through a 12-inch-diameter ConocoPhillips pipeline. ~ 2000 feet Explorer Pipeline Glenpool Tank Farm Explorer measurement facilities & delivery valves N Explorer 24” line to ConocoPhillips 12” crude oil pipeline 30” line to tank 11 9 8 7 12 11 Explorer 28” mainline ConocoPhillips Glenpool South Tank Farm Power lines Figure 1. Schematic of Explorer Pipeline Glenpool tank farm and ConocoPhillips Glen- pool South tank farm showing tank 11, pipelines, and power lines located along dike east of Glenpool South tank farm. About 4:00 p.m. at Glenpool Terminal, the ConocoPhillips operator obtained a valve lineup sheet and prepared it jointly with the outgoing shift operator for the upcoming operations. Before leaving the office for the tank farm, the operator verified how much gasoline was in the piping system so that, once the removal operation was complete, she could confirm that all the gasoline had been removed. She went to the Glenpool South tank farm about 4:30 p.m. and began transferring gasoline from the manifold piping to tank 12. When the transfer of gasoline from tank 11 to Glenpool terminal was completed, about 5:33 p.m., she transferred the gasoline in the tank’s piping to tank 12. <<>> Factual Information 3 Pipeline Accident Report When all transfers were complete, about 6:10 p.m., the operator lined up the valves so tank 11 could receive diesel from Explorer. ConocoPhillips representatives told investigators that even though no gasoline remained in the tank 11 lines or manifold piping at the conclusion of the transfer operation, about 55 barrels of gasoline remained in the tank 11 sump5 between the sump floor and the bottom of the 30-inch-diameter fill/drain pipe (which was about 21 inches above the sump floor). About 6:15 p.m. on April 7, 2003, the ConocoPhillips operator went to the office at the Explorer Glenpool tank farm and spoke with the Explorer operator. The ConocoPhillips operator confirmed with the Explorer operator that the delivery was a 24,500-barrel batch of diesel going into tank 11, which was empty (except for the residual gasoline in the sump). The diesel delivery was from Explorer’s 28-inch-diameter mainline. After the diesel was measured and sampled at the Explorer Glenpool facility, the delivery would continue through Explorer’s 24-inch-diameter line to the ConocoPhillips 30-inch-diameter line and then into tank 11. The ConocoPhillips operator also confirmed that the maximum allowable fill amount was 75,079 barrels. The ConocoPhillips operator then opened two valves in Explorer’s yard to line up the delivery; the delivery to ConocoPhillips commenced when Explorer control room personnel opened the delivery valve. Except for the opening of the delivery valve, lining up the valves, including the two valves in Explorer’s yard, was the responsibility of the ConocoPhillips operator. About 6:30 p.m., after the valve lineup was completed, the ConocoPhillips operator returned to Glenpool Terminal. About 8:33 p.m., Explorer switched the delivery of diesel to the line serving ConocoPhillips at an initial flow rate of 24,000 to 27,500 barrels per hour. The ConocoPhillips operator stated that at about 8:55 p.m., there was a high (product) level alarm in tank 11 and that this was odd because the delivery had just begun and tank 11 had been empty. The Explorer operator at the Glenpool tank farm stated that he observed a fireball but that he was near operating pumps and did not hear an explosion. He described the accident as a flash, followed by smoke and fire, after which the fire totally engulfed tank 11. He said he went to his truck and drove to the Explorer control room, where he called the Explorer central control dispatcher. He said he then drove in his truck toward the fire to verify its location. It was determined that about 8:55 p.m., after tank 11 had been filling with diesel for about 22 minutes, the tank exploded. The fixed roof separated from the tank shell and was blown northward and folded over on itself, coming to rest on top of the collapsed north wall of the tank. (See figures 2 and 3.) 5 The 15-foot-diameter by 6-foot-deep sump was in the northwest area of the tank floor, which sloped toward the sump. The design of tank 11 is discussed in more detail later in this report. <<>> Factual Information 4 Pipeline Accident Report Figure 2. View of wreckage of tank 11 facing south. Note power lines and earthen dike at left and overpressure piping at right. Figure 3. Wreckage of tank 11. <<>> Factual Information 5 Pipeline Accident Report The Explorer operator then returned to the Explorer control room, and about 8:59 p.m. closed a valve to stop the diesel delivery to ConocoPhillips and switched the delivery to other tankage in the Explorer yard. At this time, the ConocoPhillips facility was isolated from Explorer's piping system. The Explorer operator called and informed the Explorer central control dispatcher that the delivery had been switched. He also called the operator at the ConocoPhillips Glenpool Terminal. About this same time, the ConocoPhillips operator was calling the Explorer operator. The Explorer operator told the ConocoPhillips operator about the ball of fire, which they concluded was a tank on fire at the ConocoPhillips Glenpool South tank farm. The ConocoPhillips operator asked that the delivery be stopped. The two operators agreed that the Explorer operator would call 911 while the ConocoPhillips operator notified her supervisor. After the Explorer operator called 911, he called his supervisor and asked that the supervisor contact Explorer central control and have controllers shut down the 28-inch pipeline that was supplying the diesel to the Explorer facility. Explorer shut down its 28- inch-diameter pipeline at Glenpool tank farm at about 9:35 p.m. and had all tank and header valves closed by about 9:45 p.m. Explorer’s incident command was initially set up at 9:33 p.m. in the Glenpool tank farm control room and was moved to a conference room at 10:40 p.m. A resident who was inside her house, about 1,000 feet east of tank 11, reported hearing a sound like thunder that rattled her house. She said she exited her house less than 30 seconds later, at which time there was a second explosion, this one with a higher pitched sound than the first. She observed that the north side of the tank had collapsed and was on fire and that the wind was blowing the flames south. Power poles owned by American Electric Power (AEP)6 were east of the tank farm over a wall on the dike that surrounded the tank farm. The electric power facilities included three conductor wires and two shield wires7 supported by a single crossbar on dual wooden poles. Just before 6:00 a.m. on April 8, one or more wires on these poles fell to the ground. (See figure 4.) A fire then started in the unburned diesel that was being contained in the dike north of tank 11. About 6:10 a.m. on April 8, 2003, crude oil at 550 pounds per square inch, gauge (psig) was released from aboveground piping between tanks 7 and 8 inside the dike after the piping was engulfed in fire started by the power lines. The piping system provided overpressure protection for ConocoPhillips’ 12-inch-diameter crude oil pipeline. An isolation flange assembly in the piping failed because of the fire, allowing the pressurized crude oil to spray the surrounding area through the loosened flange assembly. By 6:17 a.m., ConocoPhillips had shut down the pipeline pumps and closed the remotely operated valves in the pipeline. 6 AEP, which is based in Columbus, Ohio, operates an electricity transmission and distribution grid and is the Nation’s largest electricity generator. 7 A shield wire is a grounded conductor installed to shield a phase conductor from a direct lightning strike. <<>> Factual Information 6 Pipeline Accident Report Figure 4. View of downed AEP power lines on east dike wall. The ConocoPhillips Glenpool area supervisor initially estimated that about 7,400 barrels of diesel were in tank 11 at the time of the explosion. This figure was different from the 8,420 barrels read by Explorer’s meter because some product was in the piping system downstream of the meter on its way to tank 11 when the explosion occurred. Safety Board investigators calculated the amount of diesel that was in tank 11 at the time of the explosion. These calculations were based on the amount of gasoline that was in the tank 11 sump when delivery of diesel began, the quantity of diesel metered by Explorer during the delivery, the diesel that was metered after the explosion but that did not enter tank 11, and the quantity of diesel that remained in the previously empty delivery manifold and tank 11 piping at the time of the explosion. Based on these calculations, tank 11 contained between 7,397 and 7,600 barrels of liquid (diesel and a small amount of gasoline) at the time of the explosion. Emergency Response The Glenpool Fire Department received a 911 report of tank explosion and fire at 9:00 p.m. and was on scene by 9:06 p.m., at which time tank 11 had collapsed and was engulfed by flames 75 feet high. <<>> Factual Information 7 Pipeline Accident Report The emergency response eventually involved 13 fire departments and firefighting personnel from ConocoPhillips, Sun Refinery, and Williams Fire and Hazard Control. ConocoPhillips had preplanned with Sun Refinery for mutual assistance in firefighting. Initially, the fire departments applied foam from the west side of the dike between tanks 7 and 12 and placed it around the burning tank so that the wind would disperse the foam to contain the ground fire. However, the manner in which the tank collapsed hindered the application of foam to the tank. Firefighters also applied water to tank 12, which contained gasoline, to cool it. Explorer and ConocoPhillips checked the dike drain valves to ensure that they were closed. After the power lines fell and diesel in the north area of the dike caught fire, a fire started inside tank 8 (which contained naphtha) in the area of the internal floating roof seal. This fire eventually extinguished itself, and the heat from the internal fire damaged tank 8. Also, the burning diesel in the north area of the dike caused a flange assembly in the crude oil pipeline overpressure protection system to fail and release crude oil in the area. The ConocoPhillips Glenpool area supervisor stated that because of a concern about the quantity of foam available, he called ConocoPhillips in Ponca City for additional supplies. Another ConocoPhillips employee called the Sinclair Refinery and the Tulsa airport and asked for information about available foam supplies. A staging area was set up to receive foam deliveries. In addition to a family living approximately 1,000 feet east of the tank farm, about 300 families living near the tank farm were evacuated. This was a voluntary evacuation that was lifted on the afternoon of April 9. ConocoPhillips provided housing for the evacuees. Nearby schools were closed for 2 days. Several AEP employees called the AEP transmission system operator between 9:00 p.m. and 9:30 p.m. to notify him of the accident, but he had already seen the fire on the television news. He stated that he knew the AEP power lines were near the fire. About midnight, ConocoPhillips personnel called the AEP dispatcher and requested that an AEP representative inspect the power lines near and to the east of the tank, because the flames were impinging on them. At 12:30 a.m. on April 8, an AEP servicer was dispatched to the site, and by 1:14 a.m., he had inspected the power lines and reported to the transmission system operator. No sag in the lines was observed, and the servicer, who did not communicate with any incident command staff, returned home. He did suggest to the AEP transmission system operator that an AEP representative inspect the wooden power pole near the fire, but there is no record of action being taken. About 3:43 a.m., the incident command noted that the wind had shifted to the east, but the tank 11 fire appeared contained, the cooling operation on tanks 7 and 12 was successful, and the incident appeared to be stable. Within an hour, however, the fire in tank 11 was worse, possibly because the firefighting foam inside the tank was degrading. About 5:00 a.m., after having been contacted again by on-scene personnel at 4:45 a.m., the AEP dispatcher again called the servicer at home. The transmission system operator documented in his log that the fire had restarted and was worse than before and <<>> Factual Information 8 Pipeline Accident Report that AEP should recheck the lines. The servicer returned to the scene at about 5:30 a.m. and observed that the conductor closest to the fire now had a slight sag. This indicated that heat from the fire was affecting the power line. Incident command was notified that the servicer was on site, but the servicer did not check in or otherwise communicate with incident command. About 20 minutes later, one or more wires fell onto the diked area east of the tanks and the diesel that was contained inside that area of the dike ignited. The AEP transmission system operator stated that any decision to deenergize the lines was to be made by him based on information provided by the on-site inspectors and an AEP field representative. He stated that if these lines had been deenergized, power would have been cut to the AEP substation at an Explorer pump station (not at the Glenpool tank farm) and to the pump station. No other outages would have been expected, because the system would have automatically rerouted power. The AEP transmission system operator stated that his emergency response training had not included training for nonelectrical issues. He said his training had involved neither visits to the ConocoPhillips Glenpool South tank farm nor face-to-face meetings with ConocoPhillips personnel. The AEP field representative stated that his training had been primarily on the job and that he had gained experience in actual emergencies. Meteorological Information No lightning was reported or noted in the area at the time of the explosion. The temperature was about 52° F, and the relative humidity was 54 percent. The wind was from the north at 7 mph gusting to 16 mph. ConocoPhillips Glenpool Facilities The ConocoPhillips8 Glenpool South tank farm, constructed between 1978 and 1981, was originally a Conoco facility and consisted of four storage tanks, which were designated 7, 8, 11, and 12, and one smaller tank, designated 9, that was used for mixed products. The tanks were inside a dike consisting of earthen walls and a crushed rock surface. Outside the dike were a control building, valve manifolds, product pumps, a vacuum pump and tank, and an underground sump connected to the vacuum tank. Except for tank 9, the tanks had a “drain dry” design. The floor of tank 11 was sloped to a sump inside the tank, and the 30-inch-diameter common fill/drain piping terminated in the sump. When the tank was drained dry, the only liquid that remained in the tank was approximately 55 barrels in the sump below the bottom of the fill/drain piping. 8 ConocoPhillips was founded in 2002 when Conoco, Inc., and Phillips Petroleum Company merged. <<>> Factual Information 9 Pipeline Accident Report Tank 11 and Appurtenances ConocoPhillips representatives told investigators that no as-built design or construction drawings for tank 11 could be found. According to ConocoPhillips, tanks 11 and 12 were both constructed in 1981 and were similar in design and construction. The following information was obtained from the tank nameplates, the inspection report from the tank 11 external inspection performed in July 2000, the construction specification for tanks 11 and 12, a ConocoPhillips as-built drawing of the tank 11 and tank 12 sump, and photographic evidence and known data from tank 12.9 Tank 11 was a 48-foot-high by 109-foot-diameter welded steel storage tank with a cone-type fixed roof and an internal floating roof (see figure 5). The purpose of a floating roof is to minimize emissions and evaporative losses. It floated on pontoons on top of the product and was equipped with legs that supported the roof when product was drained from the tank and the volume of liquid in the tank decreased to the level at which the roof no longer floated. The ability to “land” the roof, meaning that the roof was sitting on and fully supported by the legs, also prevented it from being damaged by contacting the tank floor. The legs typically are set so the roof is about 3 feet above the tank floor but they can be set at approximately 6 feet to facilitate personnel entering the tank and working under the roof. Pressure/vacuum vent in floating roof Vent in tank roof and shell Internal floating roof (with straps holding pontoons) Seal around floating roof 10" diameter pontoon Drain tube Support leg for roof (with sleeves at pontoon) product Flow Sump cover Sump Tank dimensions: 109' diameter x 48‘ high (drawing not to scale) 30” diameter fill/drain pipe Figure 5. Diagram of storage tank showing float - **truncated:** true - **body characters:** 131177