{"operation":"document","citation":"DCA08FP006","title":"Natural Gas Distribution Line Break and Subsequent Explosion and Fire","source_type":"incident","agency":"National Transportation Safety Board","status":"current","official":true,"published_on":"2026-01-30","effective_on":"2008-03-05","summary":"Accident. in Plum Borough, PA, USA. on 2008-03-05. Dominion Peoples Natural Gas Company. Leak/explosion/fire","machine_formats":{"json":"https://regulus.evalyn.ai/document/ntsb-case-dca08fp006.json","markdown":"https://regulus.evalyn.ai/document/ntsb-case-dca08fp006.md"},"app_url":"https://regulus.evalyn.ai/document/ntsb-case-dca08fp006","source_url":"https://www.ntsb.gov/investigations/Pages/DCA08FP006.aspx","body":"NTSB investigation DCA08FP006.\n\nEvent Type: Accident\n\nEvent Date: 2008-03-05\n\nEvent City: Plum Borough\n\nEvent State Or Region: PA\n\nEvent Country: USA\n\nPipeline Operator: Dominion Peoples Natural Gas Company\n\nPipeline Type: Distribution\n\nAccident Type: Leak/explosion/fire\n\nCompletion Status: Completed\n\nReport Number: PAB-08-01\n\nProbable cause: The National Transportation Safety Board determines that the probable cause of the leak, explosion, and fire in Plum Borough, Pennsylvania, on March 5, 2008, was excavation damage to the 2-inch natural gas distribution pipeline that stripped the pipe’s protective coating and made the pipe susceptible to corrosion and failure.\n\nTier1Name: System operating\n\nTier2Name: Fire/explosion (post-release)\n\nTier1Name: System operating\n\nTier2Name: Pipe structural malfunction/failure\n\nFinding Tier1Name: Pipeline\n\nFinding Tier2Name: Pipeline structure\n\nFinding Tier3Name: Pipe\n\nFinding Modifier Name: Damaged/degraded\n\nFinding Report Text: Pipeline - Pipeline structure - Pipe - Damaged/degraded\n\nFinding Tier1Name: Pipeline\n\nFinding Tier2Name: Pipeline structure\n\nFinding Tier3Name: Pipe coatings/anti-corrosion\n\nFinding Modifier Name: Incorrect service/maintenance\n\nFinding Report Text: Pipeline - Pipeline structure - Pipe coatings/anti-corrosion - Incorrect service/maintenance\n\nFinding Tier1Name: Pipeline\n\nFinding Tier2Name: Pipeline structure\n\nFinding Tier3Name: Pipe coatings/anti-corrosion\n\nFinding Modifier Name: Failure\n\nFinding Report Text: Pipeline - Pipeline structure - Pipe coatings/anti-corrosion - Failure\n\nOfficial NTSB investigation data. NTSB findings determine probable cause and make safety recommendations; they do not adjudicate civil liability or regulatory violations.\n\nWhat Happened\nOn March 5, 2008, about 1:39 p.m., a natural gas explosion destroyed a residence at 171 Mardi Gras Drive in Plum Borough, Pennsylvania, killing a man and seriously injuring a 4-year-old girl. Two other houses were destroyed, and 11 houses were damaged.\n\nAt 1:40 p.m., the Holiday Park Fire Department was notified about an explosioninvolving a home with two people inside. About 1:45 p.m., the police were on the scene. About 1:50 p.m., the fire chief arrived at the scene. About 1:59 p.m., an injured man was pulled from the debris. An injured girl, who had been blown free of the debris and rescued by a neighbor, received on-scene medical assistance. About 30 minutes after the explosion, a helicopter evacuated the man and the girl. The man died en route to the hospital. The local fire department declared the fire to be under control at 2:20 p.m.; at that time, the gas pipeline was feeding three small fires in the debris. The fire department remained at the scene until the fires were extinguished, at 6:59 p.m.\n\nWhat We Found\nWe determined that the probable cause of the leak, explosion, and fire in Plum Borough, Pennsylvania, on March 5, 2008, was excavation damage to the 2-inch natural gas distribution pipeline that stripped the pipe’s protective coating and made the pipe susceptible to corrosion and failure.\n\nPAB-08-01\n<<<PAGE 1>>>\n\nT\nR\nA\nN\nS\nL\nA\nN\nO\nI\nT\nA\nN\nP\nL\nU\nR\nI\nB\nU\nS\nE\nU\nM\nU N\nP\nO\nR\nT\nA\nT\nI\nO\nN\nS\nA\nF\nE\nT\nY\nB\nD\nO\nA\nR\nNational Transportation Safety Board\nWashington, D.C. 20594\nPipeline Accident Brief\nAccident No.: DCA-08-FP-006\nType of System: Natural gas distribution\nAccident Type: Leak, explosion, and fire\nLocation: Plum Borough, Pennsylvania\nDate: March 5, 2008\nTime: 1:39 p.m. eastern standard time1\nOwner/Operator: Dominion Peoples Natural Gas Company\nProperty Damage and Losses: $1,000,000\nFatalities: 1\nInjuries: 1\nMaterial Released: Natural gas\nPipeline Pressure: 10 pounds per square inch, gauge\nComponent Affected: 2-inch steel natural gas distribution pipeline\nThe Accident\nOn March 5, 2008, about 1:39 p.m., a natural gas explosion destroyed a residence\nat 171 Mardi Gras Drive in Plum Borough, Pennsylvania, killing a man and seriously\ninjuring a 4-year-old girl. Two other houses were destroyed, and 11 houses were\ndamaged. Property damage and losses were $1,000,000.\nPostaccident Investigation\nNo report of a gas odor was filed with Dominion Peoples Natural Gas Company\n(Dominion) before the accident. Several neighbors and a postal worker who were on the\nproperty 30 minutes before the explosion stated during postaccident interviews that they\nhad not smelled gas before the accident. The Pennsylvania Public Utility Commission\n(PUC) tested several homeowners to determine whether they could smell the odorant that\nindicates the presence of natural gas; each was able to smell the odorant at minimum\nlevels.\n1 All times in this brief are eastern standard time.\nNTSB/PAB-08/01\n\n<<<PAGE 2>>>\n\nEmergency Response\nAt 1:40 p.m., the Holiday Park Fire Department was notified about an explosion\ninvolving a home with two people inside. (See figure 1.) About 1:45 p.m., the police\nwere on the scene. About 1:50 p.m., the fire chief arrived at the scene. About 1:59 p.m.,\nan injured man was pulled from the debris. An injured girl, who had been blown free of\nthe debris and rescued by a neighbor, received on-scene medical assistance. About 30\nminutes after the explosion, a helicopter evacuated the man and the girl. The man died en\nroute to the hospital. The local fire department declared the fire to be under control at\n2:20 p.m.; at that time, the gas pipeline was feeding three small fires in the debris. The\nfire department remained at the scene until the fires were extinguished, at 6:59 p.m.\nFigure 1. Damage to 171 Mardi Gras Drive.\nDominion Peoples Natural Gas Company’s Actions\nDominion operated two gas distribution pipelines in the neighborhood: a 2-inch\ncarbon steel main pipeline in front of the destroyed home and an 8-inch carbon steel main\npipeline across the street from the destroyed home. (See figure 2.) The 2-inch pipeline\nprovided gas to the homes on the street; the 8-inch pipeline passed through the\nneighborhood.\nAt 1:44 p.m., Dominion was notified of the explosion by a neighbor who had called\nDominion’s emergency dispatch telephone number. At that time, Dominion dispatched\npersonnel to the scene. By 2:12 p.m., a Dominion customer serviceperson had arrived at\nthe scene. At 2:17 p.m., the maintenance crews arrived. About 2:20 p.m., Dominion\nsupervisors arrived.\n2\n\n<<<PAGE 3>>>\n\nAfter arriving, Dominion began to shut down both pipelines. According to a\nDominion crewmember, the crew had to shut off four gas control valves to stop the flow\nof gas to the two pipelines. Two other crewmembers told a Safety Board investigator that\nalthough they were able to close the shut-off valves, the valves were “a bit snug.”\nConsequently, the 2-inch pipeline was not shut down until about 5:50 p.m., and the 8-inch\npipeline was not shut down until 5:55 p.m. Dominion provided the following explanation\nfor the 4 hours needed to close the four shut-off valves. The two pipelines were two-way\nfeeds in which pressurized gas flowed from either direction; thus, shutting them down\nrequired closing four valves. Two of the four valves closed properly; however, two other\nvalves did not close completely. A Dominion crew had to dig up and fix the faulty valves\nbefore they could completely shut off the gas flow. Since the fire department had the fire\nunder control at 2:20 p.m., the 4 hours needed by Dominion to close the four control\nvalves did not increase the severity of the accident.\nIn November 2008, Dominion’s manager of delivery operations confirmed that\nDominion was in the process of reclassifying many of the shut-off valves within its\nsystem as critical valves. These critical valves are subject to more frequent inspections\nand maintenance checks in accordance with the Federal natural gas pipeline safety\nregulations in 49 Code of Federal Regulations Section 192.747. According to these\nregulations, “each valve, the use of which may be necessary for the safe operation of a\ndistribution system, must be checked and serviced, at intervals not exceeding 15 months,\nbut at least once each calendar year.” The regulations also require an operator to take\nprompt remedial action to correct any such valve found to be inoperable unless the\noperator designates an alternative valve. Non-critical valves are to be checked and\nserviced every 5 years.\nFigure 2. Diagram of accident. (North is to the right.)\n3\n\n<<<PAGE 4>>>\n\nAccording to a Dominion crewmember interviewed by a Safety Board investigator,\nthe Dominion crewmembers began bar-hole testing shortly after their arrival, at 2:17 p.m.\nTheir initial bar-hole testing focused on the 8-inch pipeline because the 2-inch pipeline\nwas a loop off the 8-inch pipeline. However, after the crewmembers noticed “bubbling”\nin the wet ground above the 2-inch pipeline and in a sewer line in front of the accident\nresidence, they started excavating these areas.\nUnder the supervision of the PUC, Dominion crews exposed the 2-inch pipeline at\n8:29 p.m. A circumferential crack ran about 270 degrees around the pipe; the top section\nof the pipe was not cracked. The pipe was bowed with a dented underside. The pipe was\nmarked and photographed. (See figure 3.) A 90-inch section of the pipe, which contained\nthe circumferential crack and the dented area, was sent to the Safety Board’s Materials\nLaboratory for examination.\nFigure 3. Cracked pipeline. (The large white mark indicates the top of the pipeline\nwhen it was excavated.)\nDuring the next 2 days, bar-hole testing was conducted every 30 minutes on the 2-\ninch pipeline, the 8-inch pipeline, and all service pipelines in the area. At 10:00 p.m. on\nMarch 6, the day after the explosion, the gas readings were recorded as high as 18.8\npercent along the 8-inch pipeline. Two days after the accident, at noon, the readings had\ndiminished to zero. During pressure tests of the repaired 2-inch pipeline, no leakage\noccurred.\nPipeline Information and Leak History\nThe 2-inch pipe had been manufactured in accordance with American Petroleum\nInstitute (API) Specification 5L Grade B standard wall thickness (that is, 0.154-inch\nnominal wall thickness). Its exterior coating had been wrapped in coal tar enamel,\n4\n\n<<<PAGE 5>>>\n\ncathodically protected, and monitored. The pipeline had been installed on\nAugust 9, 1961, as a distribution main pipeline; it had a maximum allowable operating\npressure of 30 pounds per square inch, gauge (psig) and was operated at about 10 psig.\nThe odorant used for the natural gas was a 50-50 blend of tertiary-butyl mercaptan\nand tetrahydrothiophene. Dominion’s records indicate that the odorant was in the piping\nsystem, that the odorometer tests, which were conducted before and after the accident,\nmet U.S. Department of Transportation (DOT) and Pennsylvania State requirements, and\nthat the odorant level was within prescribed concentrations. The leak history was also\nexamined, and no leaks on the 2-inch pipeline had been reported since its installation.\nThe cathodic protection pipe-to-soil potentials were all above the DOT requirement2 of\n0.85 volts.\nSafety Board’s Materials Laboratory Testing\nThe Safety Board’s Materials Laboratory examined the section of 2-inch pipe that\nwas removed from the accident site and noted that the pipe had several bends. The coal\ntar enamel coating was missing from a 3-foot section that included the pipeline’s cracked\nbottom. The bottom was also dented and deformed upward at the crack.\nGeneral corrosion was found along the length of the pipeline. Intrusions of\nintergranular corrosion were found adjacent to the crack. The loss of wall thickness was\nestimated to be about 0.010 inches at the crack. Mechanical test results were consistent\nfor a pipe that was manufactured in accordance with API 5L Grade B specifications.\nBased on the crack in the 2-inch pipeline and the results of bar-hole tests and laboratory\nexamination, the crack was the most likely cause of the release of natural gas and the\nsubsequent explosion.\nPrior Excavation Activity\nOn October 15, 2003, about 5 years before the accident, the owners of 171 Mardi\nGras Drive had hired a master plumber to replace the sewage line so that the house would\ncomply with the county code. The plumber hired an excavator to uncover the sewer line.\nThe Pennsylvania One-Call records verified that it had been notified of the excavation\nand that Dominion and the local water company had made the markouts.3\nDuring postaccident interviews with a Safety Board investigator, the plumber and\nexcavator said that they had seen the markouts and that the markouts had been properly\nplaced. The excavator said that he had used a backhoe to uncover the sewer line, that he\nhad replaced the sewer’s original terra cotta line with a plastic line, that he had backfilled\nmost of the excavation with porous sandstone, and that he had not dug near the pipeline.\nThe plumber said that he had done the digging near the pipeline and that he had done it\nby hand. Both said that they had not damaged the pipeline during the excavation.\n2 Title 49 Code of Federal Regulations 192.463 requires that a steel gas pipeline have a pipe-to-soil\nelectrical potential that exceeds 0.85 volts.\n3 A markout is a ground marking that is typically color coded and that indicates the location of\nunderground utilities.\n5\n\n<<<PAGE 6>>>\n\nThe sewer line that the plumber had installed was perpendicular to the pipeline and\ncrossed below it on the north side of the driveway. The crack in the pipeline was 5 feet\nfrom the driveway; the sewer line was 3 feet, 8 inches, from the driveway. The gas\nservice pipeline was on the south side of the driveway.\nFailure of Pipeline\nThe pipeline failure was probably rapid since no one had smelled gas 30 minutes\nbefore the explosion. The porous backfill for the new sewer line could have provided an\neasy pathway for the gas to migrate into the residence. Additionally, the crack on the\npipeline, at 10 psig, could have quickly allowed a flammable amount of gas to collect\nwithin the residence, which had many potential ignition sources.\nAccording to Pennsylvania One-Call, the only recorded excavation was the\nplumber’s replacement of the sewer line in 2003. The dents and the deformation in the\npipeline indicate that it had been struck from below by something more powerful than a\nhand shovel. The extent of the corrosion observed by the Safety Board’s Materials\nLaboratory is consistent with 5 years of in-ground exposure. Therefore, it is likely that\nthe excavator struck the pipeline with the backhoe, thereby stripping the pipeline of its\nprotective coating and making the pipeline susceptible to corrosion and failure.\nProbable Cause\nThe National Transportation Safety Board determines that the probable cause of\nthe leak, explosion, and fire in Plum Borough, Pennsylvania, on March 5, 2008, was\nexcavation damage to the 2-inch natural gas distribution pipeline that stripped the pipe’s\nprotective coating and made the pipe susceptible to corrosion and failure.\nAdopted: November 21, 2008\n6","truncated":false,"body_characters":14931}