Today, the National Transportation Safety Board determined the probable cause of the April 7, 2003, storage tank explosion and fire in Glenpool, Oklahoma was the ignition of a flammable fuel-air mixture within the tank caused by a static electricity discharge. ConocoPhillips Company was also cited for the improper manner in which they 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 (AEP) employees to recognize the risk the tank fire posed to nearby power lines and the lack of effective emergency action taken.
On April 7, 2003, at approximately 8:55 p.m., an 80,000- barrel (3.36 million gallon) storage tank at ConocoPhillips Company's tank farm exploded as it was being filled with diesel fuel. Earlier that day, gasoline had been removed from the tank. There was an explosion and resulting fire, which lasted 21 hours. There were no fatalities. Approximately 300 nearby residents were evacuated and schools were closed for two days.
"This accident illustrates the importance of safely handling hazardous liquid products," said NTSB Chairman Ellen Engleman Conners. "Our recommendations made as a result of this investigation are designed to provide a safe environment for the families living in communities near hazardous liquid storage tanks," she said.
The National Fire Protection Association and the American Petroleum Institute have guidelines for dealing with switching products in a tank and recommend precautions if the vapor space in a tank is at or above the lower flammable limit. These precautions include minimizing static generation, preventing charge accumulation, avoiding spark discharge, and controlling the environment inside the tank.
The Glenpool fire department was notified on the explosion about 9:00 p.m. and on the scene within six minutes. The emergency response involved 13 fire departments and firefighting personnel from ConocoPhillips, Sun Refinery, and Williams Fire and Hazard Control.
The AEP transmission system operator stated he was aware that the power lines were near the fire when he received the calls approximately 30 minutes after the accident occurred. Around midnight, a ConocoPhillps representative requested an AEP representative inspect the power lines near and to the east of the tank, because flames were impinging on them. An AEP servicer inspected the power lines and reported to the transmission system operator no sag in the lines was observed. The servicer returned home without communicating with an incident command staff.
On-scene personnel called AEP again at 4:45 a.m. and the servicer was dispatched again. He arrived at the scene at about 5:30 a.m., and noticed a slight sag in one of the wires. About 20 minutes later, the power lines, while still energized, fell and then ignited unburned diesel inside the dike.
Recommendations made by the Safety Board as a result of this accident include:
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.
To ConocoPhillips Company:
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.
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.
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.
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.
A synopsis of the accident investigation report, including the findings, probable cause, and safety recommendations, can be found on the Publications page of the Board's web site, www.ntsb.gov. The complete report will be available in several weeks.