{"operation":"document","citation":"DCA14MP001","title":"Birmingham Public Housing Gas Explosion","source_type":"incident","agency":"National Transportation Safety Board","status":"current","official":true,"published_on":"2021-05-18","effective_on":"2013-12-17","summary":"Accident. in Birmingham, AL, USA. on 2013-12-17. Alabama Gas Corporation. Rupture/fire","machine_formats":{"json":"https://regulus.evalyn.ai/document/ntsb-case-dca14mp001.json","markdown":"https://regulus.evalyn.ai/document/ntsb-case-dca14mp001.md"},"app_url":"https://regulus.evalyn.ai/document/ntsb-case-dca14mp001","source_url":"https://www.ntsb.gov/investigations/Pages/DCA14MP001.aspx","body":"NTSB investigation DCA14MP001.\n\nEvent Type: Accident\n\nEvent Date: 2013-12-17\n\nEvent City: Birmingham\n\nEvent State Or Region: AL\n\nEvent Country: USA\n\nPipeline Operator: Alabama Gas Corporation\n\nAccident Type: Rupture/fire\n\nCompletion Status: Completed\n\nReport Number: PAB1601\n\nReport Date: 2016-03-30\n\nProbable cause: The National Transportation Safety Board determines that the probable cause of the accident was the release of natural gas through a large crack in the 62-year-old, cast iron gas main that resulted when tree growth cracked the corroded pipe. Once the accumulating gas reached the explosive limit inside the apartment, an active pilot light on an appliance ignited the gas. Contributing to the accident was the absence of the odorant, which was absorbed by the soil and prevented residents from smelling the gas.\n\nTier1Name: System operating\n\nTier2Name: Explosion\n\nTier1Name: System operating\n\nTier2Name: Fire (post-release)\n\nTier1Name: System shutdown\n\nTier2Name: Emergency response\n\nTier1Name: System operating\n\nTier2Name: Product leak/release\n\nTier1Name: System operating\n\nTier2Name: Pipe structural malfunction/failure\n\nFinding Tier1Name: Environment/Infrastructure\n\nFinding Tier2Name: Physical environment\n\nFinding Tier3Name: Foreign object/substance\n\nFinding Modifier Name: Awareness of condition\n\nFinding Report Text: Environment/Infrastructure - Physical environment - Foreign object/substance - Awareness of condition\n\nFinding Tier1Name: Pipeline\n\nFinding Tier2Name: Pipeline structure\n\nFinding Tier3Name: Pipe\n\nFinding Modifier Name: Capability exceeded\n\nFinding Report Text: Pipeline - Pipeline structure - Pipe - Capability exceeded\n\nFinding Tier1Name: Pipeline\n\nFinding Tier2Name: Pipeline structure\n\nFinding Tier3Name: Pipe\n\nFinding Modifier Name: Not serviced/maintained\n\nFinding Report Text: Pipeline - Pipeline structure - Pipe - Not serviced/maintained\n\nFinding Tier1Name: Pipeline\n\nFinding Tier2Name: Pipeline structure\n\nFinding Tier3Name: Pipe\n\nFinding Modifier Name: Inoperative\n\nFinding Report Text: Pipeline - Pipeline structure - Pipe - Inoperative\n\nFinding Tier1Name: Environment/Infrastructure\n\nFinding Tier2Name: Conditions/weather/phenomena\n\nFinding Tier3Name: (general)\n\nFinding Modifier Name: Awareness of condition\n\nFinding Report Text: Environment/Infrastructure - Conditions/weather/phenomena - (general) - Awareness of condition\n\nFinding Tier1Name: Environment/Infrastructure\n\nFinding Tier2Name: Conditions/weather/phenomena\n\nFinding Tier3Name: (general)\n\nFinding Modifier Name: Ability to respond/compensate\n\nFinding Report Text: Environment/Infrastructure - Conditions/weather/phenomena - (general) - Ability to respond/compensate\n\nFinding Tier1Name: Pipeline\n\nFinding Tier2Name: Pipeline operation/capability\n\nFinding Tier3Name: Pipeline integrity/capacity\n\nFinding Modifier Name: Inadequate inspection\n\nFinding Report Text: Pipeline - Pipeline operation/capability - Pipeline integrity/capacity - Inadequate inspection\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\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\nAt 2:29 a.m. on December 17, 2013, one side (unit 80) of a two-story duplex at a public housing project in Birmingham, Alabama, exploded when natural gas in the apartment ignited. The explosion and fire destroyed unit 80 and heavily damaged the adjoining apartment (unit 79). The explosion also damaged several adjacent homes at the Charles P. Marks Village, operated by the Housing Authority of the Birmingham District.\nAt least three unit 80 residents were sleeping in upstairs bedrooms and were blown out\nof the apartment; two received non-life-threatening injuries. Two adults sleeping in a downstairs\n\nbedroom were crushed when the second floor collapsed. One died at the scene, and the other was\n\ncritically injured.\n\nWhat We Found\nWe determined that the probable cause of the accident was the release of natural gas through a large crack in the 62-year-old, cast iron gas main that resulted when tree growth cracked the corroded pipe. Once the accumulating gas reached the explosive limit inside the apartment, an active pilot light on an appliance ignited the gas. Contributing to the accident was the absence of the odorant, which was absorbed by the soil and prevented residents from smelling the gas.\n\nPAB-16-01\n<<<PAGE 1>>>\n\nNational Transportation Safety Board\nPipeline Accident Brief\nBirmingham Public Housing Gas Explosion\nAccident No.: DCA14MP001\nType of System: Natural gas main pipeline\nAccident Type: Rupture and fire\nLocation: Birmingham, Alabama\nDate: December 17, 2013\nTime: 2:29 a.m. central standard time\nOwner/Operator: Alabama Gas Corporation\nFatalities:\n1\nInjuries:\n3\nDamage/Clean-up Cost: $505,300\nMaterial Released: Natural gas\nQuantity Released: 147,000 cubic feet\nPipeline Pressure: 19 pounds per square inch, gauge\nMaximum Allowable\n25 pounds per square inch, gauge\nOperating Pressure:\nComponent Affected: 2-inch cast iron distribution pipeline\nThe Accident\nAt 2:29 a.m. on December 17, 2013, one side (unit 80) of a two-story duplex at a public\nhousing project in Birmingham, Alabama, exploded when natural gas in the apartment ignited.\n1\n(See figure 1.) The explosion and fire destroyed unit 80 and heavily damaged the adjoining\napartment (unit 79). The explosion also damaged several adjacent homes at the\nCharles P. Marks Village, operated by the Housing Authority of the Birmingham District.\nA Birmingham Fire and Rescue Service (BFRS) official said the six residents of unit 79\nescaped. At least three unit 80 residents were sleeping in upstairs bedrooms and were blown out\nof the apartment; two received non-life-threatening injuries. Two adults sleeping in a downstairs\nbedroom were crushed when the second floor collapsed. One died at the scene, and the other was\ncritically injured.\nThe BFRS arrived at the scene at 2:34 a.m. and extinguished the structure fire by\n3:16 a.m. Meanwhile, a separate, torch-like fire continued to burn from the broken natural gas\nservice pipeline riser adjacent to the building. (See figure 2.) Alabama Gas Corporation\n(Alagasco) crews assisted with the recovery and rescue efforts and searched for a debris-free\npath to uncover the natural gas service line to the affected apartment. At 6:14 a.m., an Alagasco\ncrew isolated the gas flow at the riser valve stopping the fire.\n1 All times in this brief are central standard time.\n201600223 NTSB/PAB-16/01\nNote: This report was reissued on April 3, 2017, with corrections to page 14.\n\n<<<PAGE 2>>>\n\nBirmingham Public Housing Gas Explosion\nFigure 1. Aerial view of the Charles P. Marks Village before the explosion.\nFigure 2. The riser fire shoots up from the ground amid the rubble at Charles P. Marks Village.\n2\nNTSB/PAB-16/01\n\n<<<PAGE 3>>>\n\nBirmingham Public Housing Gas Explosion\nThe occupants of several neighboring apartments were evacuated; many took shelter at a\nnearby recreation center. One unit 80 resident was killed, and three were injured. Alagasco\nestimated the property damage was $505,300.\nThe explosion destroyed unit 80. Unit 79, the other half of the duplex, sustained less\nsevere damage, mostly from the post-explosion fire. The common wall between units 79 and 80\npushed away from unit 80; debris from the top of the wall landed into the living areas of the\nfirst floor of unit 79. (See figure 3.)\nThe force of the explosion blew large fragments of concrete and brick into the yard, the\nalley between 64th and 65th Courtway South, and onto Joppa Avenue. The flying debris\ndamaged buildings near unit 80. Based on the location and extent of explosion-related damage,\ninvestigators determined the origin of explosion was inside unit 80.\nFigure 3. Units 79 and 80 after the explosion.\nDuring interviews by NTSB investigators, occupants of unit 79 and 80 and the\nsurrounding apartments stated they had smelled gas outside—some as far back as two weeks\nbefore the explosion. Most said they smelled gas just outside the entrance to their homes.\nOne resident said he had smelled a faint gas odor inside the home; however, no one notified\nAlagasco or the fire department the day of the explosion.\nDuring the 3 years before the incident, Alagasco had received several complaints of gas\nodors from Marks Village residents, but none involved units 79 or 80. Unit 79 and 80 residents\nsaid they had reported gas odors to the office at Marks Village, but housing authority officials\nwere unable to locate records documenting complaints for those units.\n3\nNTSB/PAB-16/01\n\n<<<PAGE 4>>>\n\nBirmingham Public Housing Gas Explosion\nNatural Gas System Examination\nA 2-inch, cast iron natural gas main operating at 19.5 pounds per square inch gauge (psig)\nran along the north side of units 79 and 80 parallel to 65th Courtway South. One and one-half-\ninch service lines supplied gas to units 79 and 80. (See figure 4.) The natural gas lines from the\nmeter outlets into the duplex consisted of threaded, black-iron pipe. The unit 80 line entered the\napartment through the wall about 3 feet above the concrete slab at the northeast corner of the\nunit. From this point, the line followed the north wall and turned south into the kitchen. The gas\nservice line continued vertically into the structure along the wall, turned horizontally directly\nbelow the second level concrete slab, and traveled the length of the kitchen toward the back of\nthe building. The pipe dropped vertically on the wall behind the sink to provide gas to the range.\nThe pipe continued downward where it supplied the water heater; it then passed through an\nadjacent wall to supply gas to the living room heater where flues for the heater and water heater\njoined and routed to a central chase in the closet with the water heater.2\nAlagasco and housing authority officials said they had no records showing the residents\nof units 79 or 80 reported gas odors either inside or outside their apartments in the 24 hours\nbefore the accident. Investigators found no evidence of a malfunctioning appliance or leaking gas\nlines in units 79 and 80.\nThe investigation showed the explosion occurred inside the unit 80 ground floor and was\ndirected outward. Evidence of this includes the entry door deformation that was indicative of an\noutward blast; the pattern of the debris field indicating debris was blown outward and away from\nthe residence; and the position of the second floor slab, which collapsed when the first floor\nwalls supporting the slab were blown outward. The NTSB investigators ruled out a gas leak\ninside the unit.\nA teenage resident of unit 80 told NTSB investigators he smelled a faint gas odor after\narriving home late the night of the accident. “I smelled it [gas] when I came in the door, but it\nwasn’t that strong, you know, so I just didn’t pay it no mind,” he said.\nAfter the accident, investigators found no evidence of pre-explosion damage to the gas\nsupply piping inside the duplex. Although there was extensive damage to the appliances,\ninvestigators found no evidence of a malfunction—determining instead that the tenants would\nlikely have detected a malfunction of the appliances that they used for heat, hot water, and\ncooking.\nThe Pipeline and Hazardous Materials Safety Administration (PHMSA) requires\noperators to odorize natural gas in distribution lines as necessary so that the gas is readily\ndetectable by a person with a normal sense of smell when the gas concentration in the air is\none-fifth of the lower explosive limit.3 Alagasco uses tertiary butyl mercaptan to odorize its\n2 “Chase” refers to the space in a building, typically behind walls where utilities are routed.\n3 Pipeline Safety Regulation 49 Code of Federal Regulations (CFR) 192.625; Odorization of Gas.\n4\nNTSB/PAB-16/01\n\n<<<PAGE 5>>>\n\nBirmingham Public Housing Gas Explosion\nnatural gas. When odorized natural gas passes through the ground from a leaking supply pipe, the\nsoil can absorb and deplete the odorant from the gas.4\nBefore the fire was extinguished, two Alagasco technicians and a supervisor arrived at\n3:28 a.m. and began conducting bar hole tests around the building along the buried gas pipe to\ndetermine the source of the gas leak.5 Technicians located multiple areas close to the scene that\nindicated the presence of leaking natural gas, including an area on the west side of Joppa Court\nadjacent to unit 80 and along 65th Courtway South north of units 79 and 80.\nThe Alagasco employees noticed bubbles in standing water that had accumulated near the\ncurb on the northeast side of the apartment, which is an indication of a subsurface gas leak.\nAt 7:14 a.m., they excavated down to the gas main and found a tree root tightly wrapped around\nthe cast iron gas main. A rock was wedged between the tree root and the cast iron pipe.\nInvestigators observed a crack in the main at that location. (See figure 4.) They confirmed the\ngas main leak using a soap solution while the line was at operating pressure. According to the\nAlagasco technician, the gas was escaping through a crack at the 5 o’clock position and was\napproximately one-quarter to one-half inch long. At 9:30 a.m., they removed the tree root,\ncleaned the pipe surface, and installed a mechanical clamp to stop the leak.\nOn December 18, 2013, Alagasco technicians cut an 8-foot segment with the newly-installed\nclamp out of gas main and replaced it with a plastic pipe. The pipe segment, rock, and tree root\nthat had been wrapped around the pipe were sent to the NTSB laboratory in Washington, DC, for\nexamination.\nFigure 4. Aerial view showing route of underground utilities near unit 80.\n4 Tenkrat, Daniel; Hlincik, Tomas; and Prokes, Ondrej (2010). Natural Gas Odorization, Natural Gas, ISBN:\n978-953-307-112-1, InTech, DOI: 10.5772/9825. Available from: http://www.intechopen.com/books/natural-\ngas/natural-gas-odorization.\n5 A bar hole survey is performed by boring a hole in soil or pavement in the area of a suspected gas leak to test\nthe subsurface environment with a combustible gas indicator. The results are read in percentage of combustible gas\nwith respect to the lower explosive limit (LEL) as a percentage of gas in air; a 100 percent reading indicates the gas\nconcentration in the bar hole is at or above the LEL. The natural gas LEL is 5 percent gas concentration in air.\n5\nNTSB/PAB-16/01\n\n<<<PAGE 6>>>\n\nBirmingham Public Housing Gas Explosion\nThe sewer and gas mains ran parallel along 65th Courtway South. Units 79 and 80\nreceive gas through service lines that branch from the main gas line in a southward direction.\nThe sewer connection for the units—made of 4-inch terra cotta—runs north from the units and\nties into an 8-inch sewer main. After the explosion, investigators excavated the 4-inch sewer\nlateral from unit 80 and discovered a 23-inch-long broken (collapsed) section. (See figure 5.)\nThe break was located approximately 20 feet from the north edge of the foundation of unit 80\nand about 25 feet south of the gas main leak.\nFigure 5. Cross section of underground piping to the northeast corner of the half-bath in unit 80.\nEmergency Response\nThe BFRS received the first 911 call at 2:29 a.m., and firefighters arrived at the scene\nwithin 5 minutes. By 3:16 a.m., firefighters had extinguished the structure fire, but not the riser\nfire. The first Alagasco service technician arrived at 3:23 a.m. followed by a supervisor at\n3:28 a.m. and additional crew members at 4:00 a.m. The first service technician began checking\nnearby sewer lines using a gas measurement instrument but detected no natural gas.\nHowever, the continuing riser fire prevented the technician from checking the sewer lines\nbetween the sewer main and unit 80.\nTwo separate fires burned during the accident, the structure fire and a riser fire at the\nnatural gas service line riser adjacent to the northeast wall of unit 80. Early in the emergency\noperation and continuing until approximately 6:30 a.m., the BFRS presumed there were no\ntrapped victims inside the burning building. This presumption was based on their search efforts\nand limited information from the other building tenants who were transported to the hospital.\nThe riser fire prevented firefighters from gaining access to the collapsed unit, which delayed a\ncomprehensive search for possible survivors.\n6\nNTSB/PAB-16/01\n\n<<<PAGE 7>>>\n\nBirmingham Public Housing Gas Explosion\nThe riser fire continued to burn while Alagasco looked for a safe, debris-free path to\nexcavate to the service line leading to unit 80 and stop the gas feeding the riser fire. The BFRS\nagreed with the decision to allow the riser to continue burning to avoid the formation of a natural\ngas cloud that could possibly re-ignite.\nAbout 6:00 a.m. when technicians were still unable to locate the buried service line to\nstop the riser fire, Alagasco decided to shut off the gas using the riser isolation valve directly\nbelow the venting, burning gas. At 6:14 a.m., the technician closed the service isolation valve,\nwhich stopped the gas flow.\nFirefighters then resumed their search and found a critically injured, conscious man\npinned beneath the second floor slab on the southeast end of the first floor of unit 80; the body of\na woman was nearby. The rescue team used airbags and hydraulic spreaders to raise the\ncollapsed second floor slab enough to rescue the man and recover the woman’s body.\nPostaccident Investigation\nNatural Gas Leak Path into Unit 80\nIn addition to the gas pipe configuration, the investigation included the examination of\nother pipes in the home, including the wastewater pipes. The 4-inch waste sewer connections\nfrom unit 80 traveled vertically through two penetrations about 29 feet apart in the first floor\nconcrete slab. The laterals then ran horizontally at approximately 32 inches below grade where\nthey were connected to the 8-inch terra cotta bell-and-spigot style sewer main.\nThe NTSB determined that one credible path for the natural gas to enter unit 80 was by\nmigrating through the soil from the cracked cast iron gas main to the buried sewer main about\n3feet away. It then traveled along the exterior of the buried sewer main to the building about\n45 feet away. (See figure 5.) It accumulated under the first floor slab and entered the unit where\nthe sewer pipe passed through the concrete slab at:\n The annulus around the 4-inch cast iron sewer pipe below a toilet located\nin the northeast corner of unit 80 on the first floor. Close examination of\nthe floor penetration around the pipe revealed gaps in the annulus.\n The 4-inch waste piping penetration through the slab near the kitchen sink,\nthe area at the annulus of the 4-inch penetration also had gaps.\nThe second credible path involved the gas leaking inside of the 4-inch sewer at the\ncollapsed section described earlier. In this scenario, gas flowed through the soil from the cracked\ngas main and into the collapsed, 4-inch sewer lateral about 22 feet away. Gas could travel inside\nthe sewer pipe and pass through the water traps in the toilet and under the bathroom sink and into\nthe ground floor. Based on the nearly 20 psig gas pressure, the expected gas flow volume out of\nthe cracked gas main, and the breach in the 4-inch sewer, natural gas likely bubbled through the\nwater seals in the toilet and the sink drains. From either route, the appliances provided the\nignition source for the gas inside the apartment; the range had three open, active pilots, and the\nroom heater had one pilot and might have had the main burner operating. (See figure 6.)\n7\nNTSB/PAB-16/01\n\n<<<PAGE 8>>>\n\nBirmingham Public Housing Gas Explosion\nFigure 6. First level of unit 80 showing areas gas entered the apartment.\nPipeline History\nNatural gas delivered to the Marks Village community is supplied through cast iron\ndistribution mains. Most of the branches are 2-inch diameter cast iron with some mains as large\nas 6 inches. The cast iron main that served units 79 and 80 was about 45 feet north of the\napartment.\nService line installation records for units 79 and 80 show the 1-1/2-inch steel service line\nwith pipe enamel coating was installed in October 1951. Gas company records did not accurately\nshow the underground routing of the service lines to the two units. Existing records did not\nidentify the pipe wall thickness used at the time of installation. Other historical information,\nincluding manufacturing and purchase records for cast iron piping in the community, was no\nlonger available. A grandfathered rule established the maximum allowable operating pressure of\nthe pipeline at 25 psig.\n6 The Alagasco records reflect that pressure testing was not performed\nbecause codes at the time of installation did not require the testing.\n6 Pipeline Safety Regulation 49 CFR 192.619 (a)(3) by using the highest actual operating pressure to which the\npipe segment was subjected to during the 5-year period preceding July 1, 1970.\n8\nNTSB/PAB-16/01\n\n<<<PAGE 9>>>\n\nBirmingham Public Housing Gas Explosion\nAlagasco maintains the integrity of its gas mains and service lines by walking surveys\nperformed on a 3-year basis through a subcontract with a qualified leak detection contractor.7\nThe contractor last surveyed the gas mains for leaks in May 2011 and surveyed the service lines\nin November 2011. All identified leaks were repaired, although the main and service lines in the\nvicinity of units 79 and 80 did not require any repair work.\nLeak Surveys\nAt the request of the NTSB, Alagasco leak-surveyed the community for indications of a\nnatural gas leak near the damaged unit 80 as well as other addresses within the property in the\ndays following the accident. In areas where technicians suspected a leak, they excavated the\nregion to approximately 3 feet below grade to expose the suspected leak location. In total,\nexcavations would involve the removal of six gas-piping segments, labeled A through F. (See\nfigure 7.) All the segments were shipped to the NTSB laboratory in Washington, DC, for\nexamination. Alagasco technicians detected gas leaks at the locations marked with the white\nrectangles. The clamp on segment A (sleeve 1 in figure 7) was installed the morning after the\nexplosion to stop the leak and stabilize the pipe for removal.\nFigure 7. Pipe segments recovered from the accident; rectangles indicate the leak locations.\n7 A “walking survey” consists of a technician walking through a neighborhood sampling the areas (pipe runs\nand meters) with electronic gas detection equipment. Leak grades and categories of interest are: Grade 1, which\nincludes (among other things) any reading of 20 percent LEL or greater at the outside of a building or where gas\nwould likely migrate to an outside wall of a building; Grade 2, which includes(among other things) any reading of\n40 percent LEL or greater under a sidewalk in a wall-to-wall paved area that does not qualify as a Grade 1 leak; and\nGrade 3 which includes (among other things) any reading less than 100 percent LEL under a street without wall-to-\nwall paving where it is unlikely that gas could migrate into a building.\nIn accordance with 49 CFR 192.723 (b)(2) Distribution leakage surveys; cathodically unprotected pipe\nrequires 3-year maximum interval.\n9\nNTSB/PAB-16/01\n\n<<<PAGE 10>>>\n\nBirmingham Public Housing Gas Explosion\nMaterials Laboratory Testing\nPrior to destructive testing, several pipe segments were pressure tested with compressed\nair at the NTSB Materials Laboratory to verify the leak locations; determine pressure decay with\ntime; and estimate the leak rate. In summary, the leak tests showed that pipe segments C, D, and\nF contained leaks in the same respective areas as those identified during the on-scene accident\ninvestigation and revealed evidence of a leak at the ends of the sleeve 2 that was not detected\npreviously. Pipe segment B was not pressure tested since Alagasco reported the leak to be at the\nthreaded connection on the segment and the fitting had been disconnected in the field.\nAlagasco technicians identified segment E to be of interest and submitted it for testing\nbecause it contained an existing sleeve. Testing revealed evidence of leaks at both ends of the\nsleeve that were not detected during the on-scene pressure testing. Visual examination of\nsegment F (a 2-inch nominal diameter cast iron pipe) revealed a 4-inch long linear indication at\nthe 12 o’clock position. Leak testing confirmed the field test results and identified two additional\nleaks at the 10 o’clock and 1 o’clock positions. The length of the 10 o’clock and 1 o’clock cracks\nmeasured approximately 3.6 inches and 2 inches, respectively, along the pipe axis.\nNTSB investigators disassembled and removed the new clamp on pipe segment A. They\ndiscovered a fracture that extended circumferentially around the pipe. (See figure 8.) The fracture\nsurface revealed a radiating pattern that originated from the outer surface at the bottom of the\npipe. The fracture extended from each side of the fracture origin and propagated\ncircumferentially up toward the top of the pipe.\nFigure 8. Pipe segment A after the new clamp was removed to expose the crack.\n10\nNTSB/PAB-16/01\n\n<<<PAGE 11>>>\n\nBirmingham Public Housing Gas Explosion\nThe fracture face exhibited five regions adjacent to the outside surface consistent with\noxidized cast iron. The largest oxidized region was located at the bottom of the pipe and\nextended through the pipe wall. The circumferential length of the oxidized region measured\napproximately 1.6 inches along the outer surface. The oxidized region at the inner surface\nmeasured approximately 0.7 inch circumferentially.\nThe dark gray area on the fracture face in the area adjacent to the outer surface indicates\nsignificant graphitic corrosion in the cast iron gas main. (See figure 9.) Graphitic corrosion\nreduced the strength of pipe segment A and made it more brittle.\nFigure 9. SEM electron backscatter image of the pipe segment A fracture face.\nIn addition, NTSB investigators examined the large tree root and rock that had been\nrecovered with the pipe segment. They concluded that the tree root around the pipe increased the\nforce exerted by the rock against the corroded cast iron pipe wall. The compressive, pinpoint\nforces exerted by the rock and downward forces from ground settlement likely caused the\ncorroded pipe to crack.\nDistribution Integrity Management\nPHMSA amended the Federal Pipeline Safety Regulations on December 4, 2009, and\nFebruary 1-2, 2010, to require operators of gas distribution pipelines to develop and implement\nan integrity management program that includes a written integrity management plan. The\nregulations took effect in 2011. Although there are required program elements, PHMSA does not\nmandate specific methods of implementation. Alagasco performs an evaluation of its Distribution\nIntegrity Management Program (DIMP) on an annual basis; plus the program is periodically\naudited by the Alabama Public Service Commission, most recently in March 2014.\nThe Alagasco cast iron management program has evolved over the last three decades.\nSince 1997, Alagasco has replaced approximately 405 miles of cast iron piping. The pipe\nreplacement program operates as a separate, but related, program from DIMP. The focus of the\npipe replacement program is to prioritize areas for replacement. Management bases the\nreplacement on evaluation of leak repair data and input from field operations personnel to create\nthe pipe replacement priority list.\n11\nNTSB/PAB-16/01\n\n<<<PAGE 12>>>\n\nBirmingham Public Housing Gas Explosion\nAlagasco analyzes 10 years of pipeline data and evaluates its list of scheduled pipeline\nreplacements on an annual basis. On the June 2013 priority list, it ranked Marks Village near the\nbottom of the priority list. Following the explosion at Marks Village, Alagasco re-ranked the\npriority list and completed the replacement of all cast iron gas pipes at Marks Village in\nMarch 2014.\nAfter the accident, Alagasco reviewed the condition of cast iron piping at 13 other Birmingham\npublic housing communities. The assessment revealed two installations of cast iron piping that\ndated back to 1917. Again, following a review of these properties, Alagasco re-ranked and\nscheduled the cast iron replacement work well ahead of the previously planned replacement\ndates. Alagasco has replaced cast iron at one of the two 1917 era communities.\nAlabama Public Service Commission Audits\nThe Alabama Public Service Commission (ALPSC) is an intrastate regulator that\noversees all operator distribution mains and service pipelines within the state of Alabama.\nThe regulator’s inspection of Alagasco encompasses the auditing of records, physical plants,\ncorrosion control programs, operator qualification, and field inspection. The ALPSC also\nconducts “protocol 9” inspections.8 These inspections cover all areas of the operation through all\nterritories of the gas company.\nIn 2012, the ALPSC sent letters to all operators of natural gas pipelines in Alabama in\nresponse to an NTSB safety recommendation from an incident in Allentown, Pennsylvania. In its\nAugust 23, 2012, letter to Alagasco, the ALPSC noted that cast iron pipe has been considered a\nserious threat to natural gas distribution systems. The ALPSC noted that the Alabama ranks\namong the top 10 states with the most cast iron piping remaining in its distribution systems.\nRecognizing the economic difficulty of large-scale replacements, the regulators called on\nAlagasco to look at cast iron replacement as a top priority. The ALPSC noted the efforts that\nAlagasco had already taken with respect to cast iron replacement and encouraged the company to\naccelerate and address replacements, particularly in business areas, as soon as practical.\nAlagasco reported that during the past five years it replaced an average of 41 miles of\ncast iron pipe per year. In its 2011 Gas Distribution System annual report, Alagasco reported it\nhas 928 miles of cast iron pipe remaining in its system. Alagasco anticipated replacing an\nadditional 35 miles in 2012 and 51 miles in 2013. As a result, Alagasco estimated it would have\nall of its cast iron pipelines replaced in approximately 20 years.\n8 Pipeline and Hazardous Materials Safety Administration, Form 15; through Amendment 195-95 -- Inspection\nreport format requiring covered task performance, qualification status, abnormal operating condition recognition and\nreaction, verification of qualification, and program inspection deficiencies.\n12\nNTSB/PAB-16/01\n\n<<<PAGE 13>>>\n\nBirmingham Public Housing Gas Explosion\nPostaccident Actions\nFollowing the accident, Alagasco reviewed its actions and response to identify potential\nareas of improvement. The postaccident actions included:\n Replaced the cast iron pipe in Marks Village in early 2014. The cast iron mains\nwere replaced with polyethylene pipe ranging from ¾-inch to 4-inch diameter.\nThe majority of the service lines were replaced with polyethylene pipe from the\nmain lines to the meter locations. In addition, Alagasco added main isolation\nvalves with the capability of stopping the flow of gas into this community if such\nan action is required in the future.\n Alagasco completed the scanning of all available service cards (service line\nlocation information), trained its field personnel in the use of the new service\ninformation, and made the information electronically accessible in the service\ntrucks.\n Initiated annual leak surveys for cast iron and unprotected steel mains serving\nmulti-family residences. These surveys were previously conducted on a 3-year\ncycle in accordance with DOT 192 requirements. Alagasco now conducts these\nsurveys annually. The first cycle for such surveys was completed in 2014.\n Met with the BFRS and created an “Emergency Response Lessons Learned”\ndocument. On August 25, 2014, Alagasco met with members of the BFRS\ninvolved in the emergency response for this incident. The purpose of the meeting\nwas to discuss Alagasco’s actions/response to the Marks Village incident and to\nallow the BFRS to provide its observations concerning the response efforts.\n Revised Alagasco’s evaluation process for future cast iron pipe replacement\nlocations. Alagasco’s evaluation process now includes analysis of leak history\nfor both mains and services.\n Prepared a special mail-out of procedures for reporting gas leaks to customers in\nmulti-family units. This was mailed in August 2014 to customers in multi-family\nunits who are served by a cast iron or bare steel gas main. It instructs customers\nto call Alagasco or 911 first (rather than the landlord or maintenance department)\nif a gas leak is suspected.\n Changed safety information processes for electronic bill customers. Alagasco\nnow ensures that customers who receive and pay their bills electronically receive\nthe same safety information (by US Mail) as those who receive their bills in\npaper format.\n13\nNTSB/PAB-16/01\n\n<<<PAGE 14>>>\n\nBirmingham Public Housing Gas Explosion\n Revised the Alagasco Customer Natural Gas Safety brochure (also known as the\nAlagasco 16-75 brochure) to include language specifically targeting customers\nliving in rental properties (including multi-family units). The first semi-annual\nmailing of the revised brochure occurred in April 2015.\n Ensured customers have continuous access to safety information through the\nwebsite, http://www.alagasco.com/safety---education/if-you-smell-natural-gas-\n58.html.\n Expanded the practice of distributing the 16-75 safety brochures to customers at\nservice calls. For the Birmingham customer base, 16-75 safety brochures were\ngiven to all customers during service calls where the mechanic interacted with\nthe customer. Alagasco has expanded that practice into all of its service areas.\nProbable Cause\nThe National Transportation Safety Board determines that the probable cause of the\naccident was the release of natural gas through a large crack in the 62-year-old, cast iron gas\nmain that resulted when tree growth cracked the corroded pipe. Once the accumulating gas\nreached the explosive limit inside the apartment, an active pilot light on an appliance ignited the\ngas. Contributing to the accident was the absence of the odorant, which was absorbed by the soil\nand prevented residents from smelling the gas.\nFor more details about this accident, visit www.ntsb.gov/investigations/dms.html and\nsearch for NTSB accident ID DCA14MP001.\nIssued: March 30, 2016\nThe NTSB has authority to investigate and establish the facts, circumstances, and cause or\nprobable cause of a pipeline accident in which there is a fatality, substantial property damage, or\nsignificant injury to the environment. (49 U.S. Code § 1131 - General authority)\nThe NTSB does not assign fault or blame for an accident or incident; rather, as specified by NTSB\nregulation, “accident/incident investigations are fact-finding proceedings with no formal issues\nand no adverse parties . . . and are not conducted for the purpose of determining the rights or\nliabilities of any person.” Title 49 Code of Federal Regulations, Section 831.4. Assignment of\nfault or legal liability is not relevant to the NTSB’s statutory mission to improve transportation\nsafety by investigating accidents and incidents and issuing safety recommendations. In addition,\nstatutory language prohibits the admission into evidence or use of any part of an NTSB report\nrelated to an accident in a civil action for damages resulting from a matter mentioned in the report.\n49 USC 1154(b).\nCORRECTED COPY\n14\nNTSB/PAB-16/01","truncated":false,"body_characters":35659}