COLUMBIA GAS TRANSMISSION CORP

Incident Narrative

TWO CONTRACT EMPLOYEES WERE WELDING OUTSIDE THE COMPRESSOR STATION BUILDING AT THE MANIFOLD OF THE EXHAUST PIPING FOR COMPRESSOR UNIT NO. 2. ALL NECESSARY HOT WORK PERMITS WERE IN PLACE AT THE TIME. THE COMPRESSOR STATION HAS THREE UNITS, NONE OF WHICH WERE OPERATIONAL AT THE TIME OF THIS EVENT. UNITS NO. 1 & 2 WERE ISOLATED WITH PROPER LOCK-OUT TAG-OUT IN PLACE PER THE COMPANY'S OPERATIONS & MAINTENANCE MANUAL. UNIT NO. 3 WAS NOT RUNNING AT THE TIME OF THE INCIDENT. THE COMPANY HAS INITIATED A ROOT CAUSE ANALYSIS (RCA) INVESTIGATION TO DETERMINE THE CAUSE OF THE INCIDENT. THE COMPRESSOR MANUFACTURER ALONG WITH A FAILURE ANALYSIS INVESTIGATIVE EXPERT (CONSULTANT) CONDUCTED THEIR INVESTIGATIONS INTO THIS INCIDENT. THE RCA REPORT IDENTIFIED THAT THE SOURCE OF IGNITION WAS ARC WELDING BEING PERFORMED ON THE EXHAUST FLANGE LOCATED OUTSIDE OF THE COMPRESSOR BUILDING. NATURAL GAS WAS PRESENT IN THE CRANKCASE VENT DUE TO A PACKING LEAK IN THE COMPRESSOR CYLINDERS OF UNIT #3. THE PACKING LEAK ON UNIT NO. 3 TRAVELED VIA A COMMON OIL DRAIN TO THE UNIT NO. 2 COMPRESSOR CYLINDER DISTANCE PIECES AND THUS INTO THE UNIT NO.2 CRANKCASE AND VENT. GAS MONITORING WAS PERFORMED USING A GAS DETECTOR AT THE VENTS, EXHAUST, STARTERS, AND SURROUNDING AREA PRIOR TO THE WELDING AND THERE WAS NO INDICATION OF A COMBUSTIBLE ATMOSPHERE. IT APPEARS THAT THE GAS MONITOR WAS NOT EXPOSED TO THE COMBUSTIBLE MIXTURE LONG ENOUGH TO PROVIDE AN ALARM TO THE OPERATOR. SHUTOFF VALVES ON THE COMMON OIL DRAIN LINE THAT SERVE TO ISOLATE EACH UNIT WERE LEFT OPEN AND WERE NOT INCLUDED AS PART OF THE LOCKOUT/TAGOUT (LOTO) PROCEDURE BEING USED AT THE TIME OF THE INCIDENT. RECOMMENDATIONS WERE NOTED AND SHARED VIA A SAFETY ALERT BROADCAST THROUGHOUT THE ENTIRE COMPANY NOTIFICATION SYSTEM. AMONG THESE RECOMMENDATIONS WERE: MANDATORY INSPECTION OF ALL UNITS AND FACILITIES COMPANY-WIDE FOR SIMILAR COMMON VENT/PIPING SYSTEMS THAT WERE FOUND AT THE INCIDENT SITE. ENGINEERING SHALL REVIEW INSPECTION RESULTS, DOCUMENTATION AND ASSURE THE NECESSARY FOLLOW-UP ACTIVITIES ARE PLANNED AND COMPLETED. REVIEW AND PERFORM MODIFICATIONS TO STATION ISOLATION LOCK-OUT/TAG-OUT PROCEDURES TO INCLUDE DRAIN AND VENT VALVES THAT ARE COMMON WITHIN A STATION THAT COULD POTENTIALLY LEAD TO A COMBUSTIBLE MIXTURE. WHEN PERFORMING ""HOT WORK"" ON A COMPRESSOR UNIT, CONSIDERATIONS SHALL BE MADE FOR EVACUATING GAS FROM ALL UNITS WITHIN THE COMPRESSOR BUILDING. IDEALLY, ANY WELDING, BURNING, OPEN FLAME OR GRINDING TASKS SHOULD BE PERFORMED IN SAFE AREAS OUTSIDE THE BOUNDARIES OF THE COMPRESSOR BUILDING. WHEN HOT WORK IS NECESSARY IN BUILDINGS WITH PRESSURIZED UNITS, IT IS CRITICAL TO ENSURE EQUIPMENT SPECIFIC ISOLATION AND LOTO PLANS ARE IN PLACE AND THAT HOT WORK PERMITS ARE EXECUTED TO ENSURE ABSENCE OF ANY FLAMMABLE/EXPLOSIVE ATMOSPHERE. LOTO PLANS SHOULD BE CHALLENGED AND REVIEWED BY OPERATIONS, ENGINEERING AND CONTRACTORS PERFORMING THE WORK BEFORE BEGINNING ANY WORK ON COMPRESSION UNITS TO IDENTIFY POTENTIAL PATHS FOR A FLAMMABLE/EXPLOSIVE MIXTURE TO OCCUR.