On January 17, 2023, natural gas liquid was accidentally released during maintenance of a natural gas liquid storage cavern in Texas. The released natural gas liquid formed a vapor cloud and ignited, causing a large fire. The fire fatally injured one contract worker and seriously injured another. The company estimated the property damage from the incident to be $3.1 million.
The gas storage cavern was used to store natural gas liquid (a mixture of mostly propane and butane). At the time of the incident, contractors were securing components of the wellhead after a maintenance operation and needed to tighten eight lockdown screws into the wellhead. A contractor used a battery-operated impact wrench, which was inadvertently left in reverse. When the contractor attempted to tighten one of the lockdown screws, the screw was accidentally removed, releasing natural gas liquid. This flammable material ignited, injuring the two workers. Both workers were transported to the hospital, where one succumbed to the burn injuries.
Cavern seals were in place for the maintenance work, which prevented any release from the cavern itself. When the lockdown pin was removed, the residual natural gas liquid was released from the hydraulic workover unit, referred to as a “snubbing unit,” which was being used for the maintenance operation. The pressure in the snubbing unit at the time of the incident was 400 pounds per square inch gauge.It was estimated that 16 barrels of natural gas liquids were released. After the incident, the company created action items to require (1) using hand tools to adjust lockdown screws on cavern wellheads and (2) establishing risk management practices to vent pressure from the snubbing unit to the flare system.
Probable Cause
Based on the company investigation and OSHA inspection, the CSB determined that the probable cause of the accidental release of natural gas liquid was the inadvertent removal of a lockdown screw from the wellhead. Contributing to the incident was the use of a battery-operated impact wrench and the presence of pressurized natural gas liquid in the snubbing unit.
Source:CSB.gov
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