Federal and state pipeline safety regulators on Wednesday released the results of a joint investigation finding procedural shortcomings by Williams' Northwest Pipeline Co. operators that led to an explosion and fire at a liquefied natural gas (LNG) peaking facility in Washington state two years ago (see Daily GPI, March 31, 2014).
The investigation of the explosion that injured five workers and evacuated the facility in Plymouth, WA, determined the leading cause was inadequate procedures that allowed oxygen to remain in the system with the resulting mix with natural gas being ignited during start-up of the peaking facility in 2014.
Working together, the U.S. Department of Transportation's Pipeline and Hazardous Materials Safety Administration (PHMSA) and Washington's Utilities and Transportation Commission (UTC) focused on the cause and identified four additional factors. In addition, UTC submitted to PHMSA a violation report and recommendations for strengthening safety and maintenance measures.
PHMSA and UTC investigators said laboratory tests concluded that under a higher pressure and lower temperature, the oxygen and gas mixture ignited spontaneously. "They confirmed that the explosion was possible under the conditions at the facility on the day of the incident," a UTC spokesperson said.
Additional factors contributing to the incident cited by the joint investigation included:
- A lack of sufficient details on procedures for employees to follow and obtain consistent results;
- Oxygen was allowed to remain trapped in portions of the LNG facility's system because procedures did not adequately address the piping configuration;
- The system's process heat was lighted before full operating pressure was reached; and
- Excess heat was created by drastic pressurization of the system immediately prior to startup.
In its violation report, UTC alleged that Northwest Pipeline violated federal pipeline regulations and recommended that a penalty be imposed. The state regulators also asked PHMSA to consider taking administrative actions or holding proceedings "to incorporate the lessons learned from the investigation to ensure that LNG liquefaction facilities like the ones in Plymouth continue to operate safely."
A notice on the Northwest Pipeline website posted in March said the company "completed the necessary repairs to restore 100% of the design capacities" at the LNG storage facility, and at that time it was going through the final stages of testing and commissioning leading to resumption of full service on April 1.
Less than a month after the incident, the source -- not the cause -- of the incident was revealed. Northwest's Ed Brewer, operations general manager at the time, said a preliminary investigation concluded that a rupture in one of the two storage tanks' pressure vessels was the source of the explosion and fire that injured five workers and required a partial evacuation of Plymouth residents (see Daily GPI, April 11, 2014).