SHELL PIPELINE CO., L.P.

Incident Narrative

IN THE PROCESS OF SEAL REPAIR A FIRE BROKE OUT ON THE IFR OF GASOLINE TANK 573. ALL WORKERS WERE SAFELY EVACUATED FROM INSIDE TANK. NO PRODUCT RELEASED TO GROUND. FIRE DEPARTMENT AND MUTUAL AID RESPONDED TO FIRE AND EXTINGUISHED FIRE. ROOT CAUSE ANALYSIS WAS CONDUCTED AND FINALIZED BY SMES. MOST LIKELY, GASOLINE VAPORS ACCUMULATED IN THE RIM SPACE DUE TO GAPS BETWEEN THE TANK WALL AND THE PRIMARY SEAL ALLOWING VAPORS TO PASS BY THE PRIMARY SEAL AND INTO THE RIM SPACE. THE LARGEST OBSERVED GAPS BETWEEN THE PRIMARY SEAL SHOE AND THE TANK WALL WERE AT THE LOCATIONS OF THE BUTT STRAPS AND RIVETS OF THE TANK WALL. GASOLINE VAPORS LIKELY BECAME TRAPPED AND ACCUMULATED IN THE SPACE BETWEEN THE INSTALLED SECTION OF NEW SECONDARY SEAL AND THE PRIMARY SEAL, CREATING A FLAMMABLE ATMOSPHERE. THE MOST PROBABLE CAUSE OF IGNITION WAS CONTACT BETWEEN THE FLAMMABLE MIXTURE OF GASOLINE VAPORS IN THE RIM SPACE WITH A HOT METAL SURFACE ABOVE THE AUTO IGNITION TEMPERATURE OF GASOLINE, AT THE LOCATION WHERE A SCREW WAS BEING USED TO INSTALL THE SECONDARY SEAL MATERIAL. THE INVESTIGATION TEAM ALSO OBTAINED THAT IF A SCREW BEING INSTALLED WITH A PNEUMATIC IMPACT WRENCH INTO THE Z-PLATE COULD GENERATE ENOUGH HEAT TO RAISE THE TEMPERATURE ABOVE THE AUTO IGNITION POINT OF GASOLINE, WHICH IS IN THE RANGE OF 480-530