LIKELY CAUSE OF GULF ACCIDENT PINPOINTED

April 23, 1990
A compressor on a subcontractor work boat probably ignited a mixture of natural gas and liquid hydrocarbons expelled when an 18 in. riser pipe was purposely cut last year in the Gulf of Mexico. The resulting explosion killed seven persons and destroyed ARCO Oil & Gas Co.'s Platform B on South Pass Block 60. Those are the findings of a Minerals Management Service, U.S. Coast Guard, and Office of Pipe Line Safety investigation of the incident.

A compressor on a subcontractor work boat probably ignited a mixture of natural gas and liquid hydrocarbons expelled when an 18 in. riser pipe was purposely cut last year in the Gulf of Mexico.

The resulting explosion killed seven persons and destroyed ARCO Oil & Gas Co.'s Platform B on South Pass Block 60.

Those are the findings of a Minerals Management Service, U.S. Coast Guard, and Office of Pipe Line Safety investigation of the incident.

The report said the mixture was released by a cold cutting operation being carried out by a Southern Natural Gas Co. contractor on Sonat's 18 in. line to the ARCO platform. The line was being cut to install a pig trap.

Sonat, meanwhile, has paid $30 million to settle several personal injury and death claims filed in New Orleans federal court as a result of the accident.

CONTRIBUTING FACTORS

Sonat believed the line was flooded with seawater, the MMS report said, but because of undulations in the 12.22 mile line pockets of gas and hydrocarbons remained.

Penetration of the riser allowed the mixture to escape. As the gas expanded, it provided the driving force to expel the liquids.

The report said there were 10 contributing factors to the accident:

  • Sonat's check valve about 350 ft from ARCO's platform was locked open, resulting in failure to isolate the section of line to be cut and limit the hydrocarbon flow.

  • A skillet was not inserted into Sonat's riser pipe before cutting.

  • Contents of Sonat's line were not determined by removing a plug just below Sonat's shutdown valve before the cut was made.

  • A Sonat 2 in. bypass about 12 miles from the platform was not properly sandbagged and protected, which started the chain of events leading to the accident.

  • The explosion under ARCO's platform ruptured numerous flow lines, which helped fuel the fire.

  • There was no detailed, coordinated plan for the repair project.

  • There was no oversight of the contractors' activities.

  • The pig trap was being installed below Sonat's 18 in. shutdown valve.

  • Restarting of the cutting tool by the contractor after penetration and release of the hydrocarbon mixture.

  • Close proximity of a work boat under subcontract to Sonat, on which the compressor is thought to be the ignition source.

Copyright 1990 Oil & Gas Journal. All Rights Reserved.