8 October 2002
Human errors blamed for fatal pipeline rupture
Washington, D.C. – The National Transportation Safety Board (NTSB) said Tuesday it has determined a 1999 gasoline pipeline rupture in Washington State was probably caused by several factors, including excavation damage and inadequate inspection. The rupture and subsequent fire killed 3 people.
On 10 June 1999, a 16-inch-diameter steel pipeline owned by Olympic Pipe Line Co. (OPLC) ruptured and released about 237,000 gallons of gasoline into a creek that flowed through Whatcom Falls Park in Bellingham, Wash. About 90 minutes after the rupture, the gasoline ignited and burned approximately 1.5 miles along the creek.
Two 10-year-old boys and an 18-year-old male died as a result of the accident; eight additional injuries were documented. A single-family residence and the city of Bellingham's water treatment plant were severely damaged.
According to the NTSB report, prior to the accident, the controller operating the accident pipeline rerouted product flow from one facility into another. As the delivery points were switched, pressure in the accident pipeline began to build back upstream. As a consequence of this rising pressure in the pipeline, a block valve at Bayview (about 23 miles downstream from accident site) closed, completely blocking the flow of product through the pipeline.
That, in turn, caused a pressure increase upstream towards Bellingham where the pipeline ruptured, the NTSB said. Simultaneous to that event, the supervisory control and data acquisition system (SCADA) system controllers used to operate the pipeline became unresponsive, preventing the controller from starting additional pumps needed to alleviate the pressure backup. Also, because of the SCADA system problems, the rupture was not promptly recognized by the controller, who restarted the pipeline.
Based on information learned during its investigation, the NTSB said it determined the probable cause of the accident was the damage done by an IMCO construction crew while conducting modifications to a water treatment plant and Olympic Pipe Line Company's inadequate inspection of work during the construction project.
NTSB said investigators found that, had the accident pipeline not been weakened by external damage, it likely would have been able to withstand the increased pressure that occurred on the day of the rupture, and the accident would not have happened.
In addition, OPLC's inaccurate evaluation of in-line pipeline inspection results led to the company's decision not to excavate and examine the damaged section of pipe, NTSB's report said.
Other NTSB findings of probable cause including OPLC's failure to test all safety devices associated with the Bayview products facility before activating the facility, its failure to investigate and correct the conditions leading to the repeated unintended closing of the Bayview inlet block valve, and the company's practice of performing other duties on the SCADA system while it was being used to operate the pipeline.
The last element led to the system's becoming non-responsive at a critical time during pipeline operations, NTSB said.
As part of its investigation, NTSB investigators said they reviewed the SCADA system which operate and controls the pipeline. It consists of field sensors and actuators, remote terminal units, a communications link, and the main SCADA computer. Field sensors and actuators include pumps, valves, temperature monitors, flow meters, and other devices to measure field data and the signal input/output to those devices. Remote terminal units collect signals from the field hardware and convert them to digital signals for transmission to the control center.
In findings cited in the report, the NTSB noted that, if the SCADA system computers had remained responsive to the commands of the Olympic controllers, the controller operating the accident pipeline probably would have been able to initiate actions that would have prevented the pressure increase that ruptured the pipeline.
The board also noted that, had the SCADA database revisions performed prior to the accident been adequately performed and tested, errors resulting from those revisions may have been identified and repaired before they could have had an affect on the pipeline's operation. Overall, the development, implementation, and protection of Olympic's SCADA system was not adequately managed, the report said.
As a result of its investigation, the board made the following recommendations to the Research and Special Programs Administration:
- Issue an advisory bulletin to all pipeline operators who use SCADA systems, advising them to implement an off-line workstation that can be used to modify their SCADA system database or to perform developmental and testing work independent of their on-line systems. Advise operators to use the off-line system before any modifications are implemented to ensure that those modifications are error-free and that they create no ancillary problems for controllers responsible for operating the pipeline.
- Develop and issue guidance to pipeline operators on specific testing procedures that can (1) be used to approximate actual operations during the commissioning of a new pumping station or installation of a new relief valve, and (2) be used to determine, during annual tests, whether a relief valve is functioning properly.
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