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Sonat Exploration Co. Catastrophic Vessel Overpressurization

At approximately 6:15 p.m. on March 4, 1998, a catastrophic vessel failure and fire occurred near Pitkin, Louisiana, at the Temple 22-1 Common Point Separation Facility owned by Sonat Exploration Co. Four workers who were near the vessel were killed, and the facility sustained significant damage. The vessel lacked a pressure relief system and ruptured due to overpressurization during start-up, releasing flammable material which ignited.

At approximately 6:15 p.m. on March 4, 1998, a catastrophic vessel failure and fire occurred near Pitkin, Louisiana, at the Temple 22-1 Common Point Separation Facility (the “facility”), owned by Sonat Exploration Co.1 Four workers who were near the vessel were killed, and the facility sustained significant damage. The facility housed two petroleum separation trains2 and consisted of separation equipment, piping, storage vessels, and a gas distribution system. The separation trains were designed to produce crude oil and natural gas from well fluid,3 derived from two nearby wells. The vessel ruptured due to overpressurization, releasing flammable material which then ignited. Because of the serious nature of the incident the Chemical Safety and Hazard Investigation Board (CSB) initiated an incident investigation. The purpose of this investigation was to identify the root causes of the incident and make safety recommendations as appropriate.

ES.2 INCIDENT On the day of the incident, one of the two separation trains was to be put in operation and production was to be initiated from a new well, known as the Temple 24-1 well. This well was located approximately two miles from the facility and was connected to the facility by a pipeline. Facility supervisors intended to purge the pipeline by opening the 24-1 well and using well fluid to displace air out of the pipeline and through a storage tank roof hatch, located at the end of the production train. Purging is a common practice in petroleum production and processing and entails the removal of air from systems that will subsequently contain flammable hydrocarbons. This purging process was initiated and then conducted for approximately 60 minutes, until 6:15 p.m., at which point a separation vessel failed catastrophically, releasing flammable gas that ignited. Gas from the ruptured vessel produced a large fireball, which damaged nearby piping and released and ignited additional flammable materials. Four workers, who were in the vicinity of the vessel when it failed, died instantly due to massive trauma. The separator, four personal vehicles, and a backhoe were destroyed, and there was damage to oil and water storage tanks. Two other workers who were present at the facility at the time of the incident both survived without injury.

Key numbers at a glance

Recommendations

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Cost in millions (if known)

Deaths (direct)

Recommendations

1. The separation vessel that failed, a third-stage separator, lacked an inlet valve and therefore could not be isolated from an adjacent bypass line, which at the time of the incident contained high-pressure purge gases.

2. At the time of the incident, two outlet block valves on the separator were closed, as were two block valves on the bypass line downstream of the separator. Accordingly the high pressure purge gases could not be vented and the separator was over pressurized.

3. The third-stage separator was only rated for atmospheric pressure service. The purge gas stream to which the separator was exposed had a pressure potentially as high as 800 psi.

4. The separator was not equipped with any pressure-relief devices, and over pressurization caused the separator to fail catastrophically.

5. The CSB could not conclusively determine the timing of the closure of the two bypass line block valves or establish any reason for this action.

6. The facility was designed and built without effective engineering design reviews or hazard analyses.

7. Workers at the facility were not provided with written operating procedures addressing the alignment of valves during purging operations.

8. Sonat operated third-stage separators that lacked adequate pressure-relief systems at other oil and gas production facilities for over a year prior to the incident.

9. ANSI/API Specification 12J-19926, issued by the American Petroleum Institute, describes recommended practices for the installation of pressure-relief devices on oil and gas separators. The specification states that “all separators, regardless of size or pressure, shall be provided with pressure protective devices . . . .”

10. The Occupational Safety and Health Administration’s (OSHA) Process Safety Management (PSM) Standard (29 CFR 1910.119) contains elements that are relevant to this incident, such as process hazard analyses and the use of written operating procedures. However, the PSM standard does not currently apply to oil and gas production facilities.