{"operation":"document","citation":"DCA17FP006","title":"UGI Utilities Natural Gas-Fueled Explosion","source_type":"incident","agency":"National Transportation Safety Board","status":"current","official":true,"published_on":"2019-02-25","effective_on":"2017-07-02","summary":"Accident. in Millersville, PA, USA. on 2017-07-02. UGI Utilities. Leak/explosion/fire","machine_formats":{"json":"https://regulus.evalyn.ai/document/ntsb-case-dca17fp006.json","markdown":"https://regulus.evalyn.ai/document/ntsb-case-dca17fp006.md"},"app_url":"https://regulus.evalyn.ai/document/ntsb-case-dca17fp006","source_url":"https://www.ntsb.gov/investigations/Pages/DCA17FP006.aspx","body":"NTSB investigation DCA17FP006.\n\nEvent Type: Accident\n\nEvent Date: 2017-07-02\n\nEvent City: Millersville\n\nEvent State Or Region: PA\n\nEvent Country: USA\n\nPipeline Operator: UGI Utilities\n\nAccident Type: Leak/explosion/fire\n\nCompletion Status: Completed\n\nReport Number: PAB1901\n\nReport Date: 2019-02-25\n\nProbable cause: The National Transportation Safety Board determines that the probable cause of the natural gas explosion at 206 Springdale Lane was an improperly installed mechanical tapping tee that leaked and allowed gas to migrate into the house where it ignited.\n\nTier1Name: Post-release\n\nTier2Name: Explosion\n\nTier1Name: Post-release\n\nTier2Name: Fire (post-release)\n\nTier1Name: Emergency response\n\nTier2Name: Emergency response\n\nTier1Name: Post-release\n\nTier2Name: Evacuation\n\nTier1Name: System operating\n\nTier2Name: Product leak/release\n\nFinding Tier1Name: Pipeline\n\nFinding Tier2Name: Pipeline handling/service\n\nFinding Tier3Name: Operating information\n\nFinding Modifier Name: Related operating info\n\nFinding Report Text: Pipeline - Pipeline handling/service - Operating information - Related operating info\n\nFinding Tier1Name: Pipeline\n\nFinding Tier2Name: Pipeline handling/service\n\nFinding Tier3Name: Operating information\n\nFinding Modifier Name: Capability exceeded\n\nFinding Report Text: Pipeline - Pipeline handling/service - Operating information - Capability exceeded\n\nFinding Tier1Name: Personnel\n\nFinding Tier2Name: Experience/knowledge\n\nFinding Tier3Name: Knowledge\n\nFinding Modifier Name: Not specified\n\nFinding Report Text: Personnel - Experience/knowledge - Knowledge - Not specified\n\nFinding Tier1Name: Pipeline\n\nFinding Tier2Name: Pipline systems/equipment\n\nFinding Tier3Name: Fittings\n\nFinding Modifier Name: Malfunction\n\nFinding Report Text: Pipeline - Pipline systems/equipment - Fittings - Malfunction\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 July 2, 2017, at 12:32 p.m. eastern daylight time, a natural gas-fueled explosion occurred at a single-family residence at 206 Springdale Lane, Millersville, Pennsylvania. The explosion killed one person and injured three others, destroyed the residence and significantly damaged six neighboring homes, one of which was subsequently condemned.\n\nWhat We Found\nWe determined that the probable cause of the natural gas explosion at 206 Springdale Lane was an improperly installed mechanical tapping tee that leaked and allowed gas to migrate into the house where it ignited.\n\nPAB-19-01\n<<<PAGE 1>>>\n\nNational Transportation Safety Board\nPipeline Accident Brief\nUGI Utilities Natural Gas-Fueled Explosion\nMillersville, Pennsylvania\nJuly 2, 2017\nThe Accident\nOn July 2, 2017, at 12:32 p.m. eastern daylight time, a natural gas-fueled explosion\noccurred at a single-family residence at 206 Springdale Lane, Millersville, Pennsylvania.1 The\nexplosion killed one person and injured three others, destroyed the residence and significantly\ndamaged six neighboring homes, one of which was subsequently condemned.\n2 (See figure 1.)\nFigure 1. Debris field at cul-de-sac area where explosion occurred.\nAt 10:26 a.m., a neighborhood resident walking in the area smelled natural gas and reported\nit to the local gas utility, UGI Utilities, Inc. (UGI).\n3 About half an hour later, a UGI service\n1 All times in this accident brief are eastern daylight time.\n2 Local authorities condemned the residence at 202 Springdale Lane.\n3 On June 1, 1882, UGI is incorporated in Philadelphia as the United Gas Improvement Company, becoming the\nfirst public utility holding company in the United States. In February 1968, the company changed its name to UGI\nCorporation.\nNOTE: This report was reissued on October 26, 2023, with corrections to the timeline on pages 2\nthrough 4 and corrections to the gas reading on page 4.\nNTSB/PAB-19/01\n\n<<<PAGE 2>>>\n\nUGI Utilities Natural Gas-Fueled Explosion\ntechnician arrived to investigate and confirm the gas leak.\n4 A Lancaster Area Sewer Authority\n(LASA) employee arrived on scene in response to UGI’s Emergency PA (Pennsylvania) One Call\nto mark the location of the sewer lines.5 About 15 minutes prior to the explosion, UGI personnel\ndirected the resident of 206 Springdale Lane to evacuate the residence who left in their personal\nautomobile. About 12:15 p.m., UGI requested fire department support. The first fire truck arrived\nat 12:28 p.m. and assumed a stand-by position. The house exploded about 4 minutes later.\nFollowing the accident, the natural gas main and service pipelines for the cul-de-sac homes\nwere leak tested. All segments held pressure, except for the service line at the 206 Springdale Lane\nconnection at the main; this segment had a Permalock mechanical tapping tee.6 Subsequent\ninspection of the Permalock mechanical tee revealed gas was leaking at the connection of the tee\nto the 2-inch main, and two of the four nylon bolts had fractured. At the time of the accident, the\noperating pressure of the line was 54 pounds per square inch, gauge (psig), as measured at the\nclosest monitoring point that was about 0.5 mile away from 206 Springdale Lane.\nThe Pipeline System\nThe natural gas main on Springdale Lane was made from a polyethylene material that was\ninstalled on August 7, 1995. The maximum allowable operating pressure (MAOP) of the system\nmain serving Springdale Lane was 60 psig.\nThe service line to the 206 Springdale Lane residence was installed in June 1998, and was\nconstructed of 1/2-inch polyethylene pipe. The mechanical tapping tee was installed at the same\ntime as the service line. The mechanical tapping tee and service pipe had been in service for\n19 years when the accident occurred.7 The pipe between the main and the meter at the residence\nwas 50 feet long. The service line to the residence was inserted inside a 1-inch polyethylene pipe\nthat served as a protective jacket. The jacket ran from the outlet of the service tee to the meter.\nUGI Actions Following the Gas Leak Report\nShortly after the gas leak report, UGI dispatched a UGI technician to respond. At\n11:00 a.m., the technician arrived on scene and began his assessment to determine the presence of\na leak. Consistent with UGI policy and training, the technician began implementing UGI’s leak\nsurvey procedure. His investigation determined that the leak source was at an adjacent residence,\nwhich was 206 Springdale Lane.\nAt 11:18 a.m., the technician called the on-call UGI senior supervisor of Operations\nConstruction and Maintenance (senior supervisor). The technician requested a response crew\nbecause he measured high-gas-concentration readings and confirmed a leak. The technician told\nthe senior supervisor that he suspected that a mechanical tee was leaking, and that he measured a\n4 UGI refers to its service technicians as mechanics. Each mechanic has a “grade” designation of I, II, or III, which\nis determined by the degree of qualifications and experience.\n5 For additonal information, see http://www.pa1call.org/PA811/Public/.\n6 The Honeywell Elster Perfection PermaLock Mechanical Tapping Tee is a tee that can be installed on a main to\nsupply the individual gas service to a gas customer without the need to shut down the natural gas main.\n7 UGI Gas Operations Manual, section 70.20.\n2\nCORRECTED COPY\n\n<<<PAGE 3>>>\n\nUGI Utilities Natural Gas-Fueled Explosion\nreading of 80 percent gas in the sewer and 98 percent gas over the tee. Based on the gas readings,\nthe technician classified the leak as an emergency leak. The senior supervisor contacted UGI\nDispatch at 11:20 a.m. and requested that they call Emergency PA One Call to mark underground\nutilities because an excavation would be necessary. The Emergency PA One Call ticket was issued\nat 11:27 a.m.\nAbout 11:20 a.m., the senior supervisor began looking for a crew to respond to the leak.\nUsing the UGI duty roster of employees available to respond to emergencies, the senior supervisor\nmade several calls between 11:25 a.m. and 11:44 a.m. to the on-call duty operator, who is required\nto answer all calls for response during off hours, including weekends; however, that duty operator\ndid not respond. The senior supervisor contacted the next duty operator appearing on the on-call\nlist, who answered and agreed to respond to the scene. By 11:50 a.m., the senior supervisor had\nidentified a crew to respond at the site.\nAfter identifying the response crew, the senior supervisor traveled to the scene. The senior\nsupervisor told National Transportation Safety Board (NTSB) investigators that prior to arriving\non-scene he reviewed the location of the closest shutoff valve to the site. On his way to the shutoff\nvalve, he contacted the UGI engineer and informed her that he expected to shut down a main line.\nAs the duty supervisor, the senior supervisor could exercise judgement to determine whether it\nwas appropriate to either squeeze off the line or close a gas valve.8 After the discussion with other\nresponding UGI employees, the senior supervisor decided to squeeze off the main line rather than\nclosing the mainline valve, because he thought this action was the fastest way of stopping the flow\nof gas. Figure 2 shows the location of the valve.\nFigure 2. Location of gas shut-off valve in relation to accident site.\nThe senior supervisor told NTSB investigators that the following factors influenced his\ndecision to squeeze off the main: he considered that given the circumstances surrounding the leak,\n8 To squeeze off a line is a method of controlling either the pressure or the flow through a plastic pipe by reducing its\ncross-sectional area by applying an external force.\n3\nCORRECTED COPY\n\n<<<PAGE 4>>>\n\nUGI Utilities Natural Gas-Fueled Explosion\neven if the valve were turned off, the gas would continue to flow to the leak until the system lost\npressure; and the line could be quickly and successfully excavated and squeezed, as compared to\nthe time necessary to reach the valve.\nThe senior supervisor stated that he received a phone call from the technician, who said\nthat he had measured a lower explosive limit (LEL) of 11 percent in the basement at 202 Springdale\nLane and that he could not gain access to the house at 206 Springdale Lane.9 The senior supervisor\ninformed the technician that he should do whatever was necessary, including a forced entry, to\nclear the house at 206 Springdale Lane.\nShortly after noon, the senior supervisor arrived at the scene and continued making calls\nfrom his vehicle to his management and others to keep them abreast of the situation. Within\n10 minutes of arriving, the senior supervisor made an assessment that the fire department was\nneeded. At 12:14 p.m., he called UGI Dispatch to request that they call 9-1-1, which was\naccomplished 1 minute later. A second UGI technician arrived on the scene at 12:19 p.m.\nThe senior supervisor and the duty operator began excavating the gas main pipeline. The\nfirst UGI technician on the scene had twice visited the residence (202 Springdale Lane) to the left\nof the accident house and had talked with the residents. The LEL measurement on the first visit\nwas 10 percent. Returning 30 minutes later, he advised the residents of 202 Springdale Lane that\nthere was no need to evacuate as the LEL measurement was at 11 percent, which is less than UGI’s\n20 percent LEL threshold for resident evacuation.\nWhile the main line was being excavated, the occupant of 206 Springdale Lane responded\nto the first UGI technician’s knocks on the door. Based on the gas concentration readings of 10 to\n11 percent gas in air in the house, which would represent about 200 percent LEL concentration\n(well above UGI’s 20 percent LEL threshold for resident evacuation), the technician decided to\nevacuate the house.\n10 The occupant requested permission to leave in her personal vehicle that was\nstored in the garage. Although the technician did not allow the occupant to use her powered garage\ndoor opener, he allowed the occupant to start her vehicle in the garage and depart the area. The\nelectrical power to the neighborhood remained energized at the time of the accident.11\nThe UGI technician, who had first arrived on the scene, was near the gas meter for 206\nSpringdale Lane when the explosion occurred. The two gas employees, who were digging at the\nmain in front of the house, had fully excavated the plastic main and were ready to squeeze-off the\nplastic main line when the explosion occurred. The representative from LASA was walking in the\ncul-de-sac when the explosion occurred. The technician located near the gas meter was killed and\nthree others were injured.\n9 Lower explosive limit (LEL) is the minimum concentration of vapor (percentage by volume) in air below which\npropagation of a flame does not occur in the presence of an ignition source.\n10 Atmospheres containing gas concentrations between 5 to 17 percent will support ignition and are considered\nhighly flammable.\n11 At 12:59 p.m., the UGI Dispatch contacted the local electric power provider, PPL Electric Utilities (PPL), and\nrequested that they shut off the power to the area. At 1:08 p.m., PPL confirmed that the electric power was shut off\nand that its personnel were on site.\n4\nCORRECTED COPY\n\n<<<PAGE 5>>>\n\nUGI Utilities Natural Gas-Fueled Explosion\nTechnician Experience and Qualifications\nThe technician, who was killed in the explosion, had over 16 years of utility experience. In\n2001, he started working at UGI. He was a technician in the Construction and Maintenance\ndepartment. Since April 2003, he held an Investigating Leak and Odor Complaints qualification.\nHe held 73 operator qualification tasks that covered all aspects of gas utility work, including\nemergency response, pipe joining, repair and maintenance, and inspection activities. Since 2013,\nhe had responded to and resolved 446 emergency calls. Of those 446 calls, 238 were gas leaks. Of\nthose 238 leaks, 27 were hazardous underground gas leaks.\nMechanical Tapping Tees\nNTSB’s examination of the tee assembly involved in the accident revealed the assembly\nwas incorrectly installed because a locking sleeve, an important piece of hardware that served as\nan attachment between the tee and the main, was not attached to the main. The tee is also secured\nto the main by four nylon bolts. Although four nylon bolts were installed, two of them were\nfractured. Since the locking sleeve was not attached to the main, additional tensile stress was\nplaced on the four nylon bolts, which then become the fail-safe feature holding the tee assembly\nin place. The NTSB determined two of the four nylon bolts fractured when in service in a manner\nconsistent with slow crack growth. The incorrect installation of the tee, combined with the\nin-service fracture of the two nylon bolts, allowed gas to escape from the tee assembly. See Safety\nRecommendation Report PSR-18/01 Installation of PermaLock Mechanical Tapping Tee\nAssemblies, including Safety Recommendations P-18-001 through -004, for details pertaining to\nexamination and testing of tee assemblies.\nPostaccident Actions\nUGI took the events of July 2, 2017, as an opportunity to reinforce and enhance the\nprocedures and programs specifically revolving around emergency response to ensure employee\npreparedness, competence, and confidence when responding to emergency situations. The\nfollowing summarizes the emergency response improvements UGI implemented across\ndepartments and job functions:\n1. System Improvement Initiatives\nImmediately following the accident, UGI instituted the following initiatives to manage the\nintegrity of the system on Springdale Lane from the intersection of Burr Oak Drive west to the end\nof the cul-de-sac. UGI implemented the following improvements:\n• Conducted a daily driving leak survey of the main in the neighborhood\n• Remediated or replaced all known mechanical tees\n• Replaced the entire gas main\n5\n\n<<<PAGE 6>>>\n\nUGI Utilities Natural Gas-Fueled Explosion\n• Took actions to manage the integrity of the surrounding neighborhood defined by\nthe boundaries of North Duke Street, Blue Rock Road, Letort Road, and Little\nConestoga Creek\n2. Pipeline and Public Safety Improvements\nThe UGI Pipeline and Public Safety department undertook several training initiatives to\nemphasize the incident command system. Outreach efforts with external emergency response\ndepartments was increased to strengthen the awareness of natural gas pipeline safety.\n3. Training and Field Compliance Improvements\nUGI updated its training to improve the skill set of its employees when responding to an\nemergency.\n4. Pipeline Facility Improvements\nUGI implemented pipeline facility enhancement to ensure the safe and reliable delivery of\nnatural gas to its customers. This enhancement included the increased remediation activity of\nmechanical tees throughout its distribution system, by either remediating or replacing 2,577 total\nmechanical tees since the accident [through October 4, 2018]. UGI continues to examine the main\nand service facilities to determine the mechanical tees that must be replaced.\n5. Dispatch Improvements\nUGI modified its dispatch procedures and protocols. UGI streamlined dispatch processes\nto proactively identify the need for electrical shutdown and additional help.\n6. Standard and Procedure Improvements\nUGI created an emergency plan that is separate from its Gas Operations Manual (GOM).\nUGI’s emergency plan contains similar content as previously included in GOM 60.50– Emergency\nPlan; however, the procedures have been revised to add further clarity to the emergency response\nsituations and the actions undertaken.\n7. 9-1-1-Related UGI Initiatives\nTo enhance safety and to ensure 9-1-1 emergency responders are timely notified, UGI:\n• Developed a first-hour checklist for first responders that provides guidance on when\nto (1) contact the local emergency response agencies: 9-1-1 and Emergency\nMedical Services, (2) shut off electrical power in the area, and (3) conduct an\nevacuation\n• Updated its response procedures to include “safety perimeter\" criteria\n• Reinforced the discretion that UGI’s first responders must shut down a pipeline\n6\n\n<<<PAGE 7>>>\n\nUGI Utilities Natural Gas-Fueled Explosion\n• Created checklists for leak investigations\n• Identified in its emergency response procedures specific emergency situations\nwhere immediate 9-1-1 notification is required by UGI personnel\n• Reviewed and updated its dispatch procedures to include a decision matrix\n• Identified situations and keywords where immediate 9-1-1 notification is required\n8. Safety Culture Assessment Project\nIn June 2018, UGI contracted DuPont Sustainable Solutions (DSS) to assess the UGI safety\nculture and the efficacy of UGI safety-related initiatives and incident investigation process to\ncreate a unified safety brand. The assessment included a comprehensive evaluation that provided\na baseline to understand the current state and the development of an improvement strategy to\nadvance the culture, systems, and processes as part of a world-class safety program.\nPennsylvania Public Utility Commission Enforcement Action\nOn October 4, 2018, the Pennsylvania Public Utility Commission Bureau of Investigation\nand Enforcement, issued a formal complaint against UGI that proposed a cumulative civil penalty\nof $2,090,022. This complaint, which was an enforcement action of that regulatory agency, alleged\nseveral safety violations that occurred during the gas leak response on Springdale Lane.\nPreviously Issued Safety Recommendations\nAs a result of this natural gas-fueled explosion on June 25, 2018, the NTSB issued the\nfollowing four safety recommendations:\nTo the Pipeline and Hazardous Materials Safety Administration:\nWork with state pipeline regulators to incorporate into inspection programs, a\nreview to ensure that gas distribution pipeline operators are using best practices\nrecommended by the manufacturer in its distribution integrity management\nprograms, including using the specified tools and methods, to correctly install\nPermalock mechanical tapping tee assemblies. (P-18-001)\nSafety Recommendation P-18-001 is classified Open—Initial Response Received.\nReference the use of external sources of information for threat identification in your\nfrequently asked questions for preparation of distribution integrity management\nprograms. (P-18-002)\nSafety Recommendation P-18-002 is classified Closed-Acceptable Action.\n7\n\n<<<PAGE 8>>>\n\nUGI Utilities Natural Gas-Fueled Explosion\nTo Honeywell International, Incorporated:\nUpdate your Permalock mechanical tapping tee assembly installation instructions\nto specify the exact tools that should be used during installation and explain what\nan installer should sense while using those tools throughout the installation process.\n(P-18-003)\nSafety Recommendation P-18-003 is classified Open—Initial Response Received.\nSpecify in your Permalock mechanical tapping tee assembly installation\ninstructions a not-to-exceed torque limit for Nylon bolts and have that value\nchecked and adjusted with a torque wrench immediately after installation.\n(P-18-004)\nSafety recommendation P-18-004 is classified Open—Initial Response Received.\nProbable Cause\nThe National Transportation Safety Board determines that the probable cause of the natural\ngas explosion at 206 Springdale Lane was an improperly installed mechanical tapping tee that\nleaked and allowed gas to migrate into the house where it ignited.\nFor more details about this accident, visit www.ntsb.gov/investigations/dms.html and search for\nNTSB accident identification number DCA17FP006.\nIssued: February 25, 2019\nRevised: October 26, 2023\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 or substantial property damage,\nor significant injury to the environment. (49 U.S. Code, Section 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 U.S. Code, Section 1154(b).\n8\n\nPSR-18-01\n<<<PAGE 1>>>\n\nNational Transportation Safety Board\nWashington, DC 20594\nSafety Recommendation Report\nInstallation of PermaLock Mechanical\nTapping Tee Assemblies\nAccident/Incident Number: DCA17FP006\nOperator: UGI Utilities, Inc.\nAccident: Residential Natural Gas Explosion\nLocation: Millersville, Pennsylvania\nDate: July 2, 2017\nRecommendation Number: P-18-1 through -4\nAdopted: June 18, 2018\nThe National Transportation Safety Board (NTSB) is providing the following information\nto urge the Pipeline and Hazardous Materials Safety Administration (PHMSA) and Honeywell to\ntake action on safety recommendations intended to prevent the incorrect installation of PermaLock\nmechanical tapping tee assemblies in gas distribution systems. These recommendations are derived\nfrom our ongoing investigation of a fatal accident involving a natural gas explosion and fire in\nMillersville, Pennsylvania. The NTSB is issuing two recommendations to PHMSA and two\nrecommendations to Honeywell.\nOngoing Investigation\nOn July 2, 2017, at 12:32 p.m. eastern standard time, a natural gas explosion and fire\ndestroyed a single-family residence at 206 Springdale Lane, in Millersville, Pennsylvania. One\nperson died, and three people were injured. Two nearby residences were severely damaged and\ncondemned for demolition. The NTSB investigation is ongoing, and the cause of the accident has\nnot been determined.\nUGI Utilities, Inc. (UGI) supplied natural gas to the Millersville residences through a\nplastic natural gas pipeline (main) and service lines, which UGI operated at a pressure of 54 pounds\nper square inch, gauge. The main was 2 inches in diameter and made of Aldyl polyethylene; the\n0.50-inch diameter service lines were made of polyethylene. Postaccident, the main and service\nlines at the accident site were pressure tested, which indicated that a PermaLock mechanical\ntapping tee assembly was leaking gas at the connection of the tee assembly to the main in front of\nthe destroyed residence. UGI installed the tee assembly in June of 1998; it had been in service for\n19 years when the accident occurred. (See figure.)\n58092 PSR-18/01\n\n<<<PAGE 2>>>\n\nStop (for cap)\nTo\nservice\nline\nStop (for the outer lip portion\nof the locking sleeve)\nFigure. Cross-section diagram of an exemplar PermaLock mechanical tapping tee assembly,\nprovided by Honeywell.\nPermaLock Mechanical Tapping Tee Assembly\nPerfection Corporation, later known as Elster Perfection Corporation, which is currently a\ndivision of Honeywell, manufactured the PermaLock mechanical tapping tee assembly involved\nin the accident.\n1 Since 1987, three versions of the PermaLock tee assembly have been\nmanufactured, and millions of the tee assemblies have been sold worldwide.2 Each of the three\nversions has a different cutter tool design and method of attaching the tower to the main. The tee\nassembly in this accident was manufactured in 1998; it was the third version. The tee assembly\nwas made of medium density polyethylene and consisted of a tower (upper half) and a base (lower\n1 For simplicity, in this report, the NTSB will use Honeywell as the umbrella company name encompassing the\nElster Perfection Corporation and the Perfection Corporation.\n2 The first version of the PermaLock tee assembly had a flat cap and a one-piece cutter design that projected into\nthe main; it was manufactured from 1987 to 1990. The second version had a domed cap and a cutter with a retractable\ncenter piece; it was manufactured from 1990 to 1996. The third version has a flat cap, a cutter tool, and a locking\nsleeve, and it is shipped with a depth tube; manufacturing of this version began in 1995 and continues today, in 2018.\n2\n\n<<<PAGE 3>>>\n\nhalf) joined together around the outer surface of a main by four Nylon 6/6 bolts.3 The tower\ncontained an internal circular steel cutter tool and a steel locking sleeve.4\nHoneywell ships the third version of the tee assembly with general written installation\ninstructions and a plastic depth tube.5 The depth tube is provided so that the person installing the\ntee assembly can verify that the locking sleeve attaches to the main. According to the written\ninstructions, the cutter tool pierces a hole in the main, and the locking sleeve attaches the tower to\nthe main. The cutter tool is then decoupled (separated) from the locking sleeve and remains stored\nin the tower for the service life of the tee assembly.\nNTSB examination of the PermaLock tee assembly involved in the accident has revealed\nthat the tee assembly was incorrectly installed. Although the cutter tool pierced a hole in the main,\nthe locking sleeve did not progress down far enough into the tower to form threads in that hole. As\na result, the locking sleeve was not attached to the main.6 The NTSB also found that two of the\nfour Nylon bolts on the tee assembly were fractured in a manner consistent with slow crack\ngrowth.\n7 These findings indicate the likelihood of varying tee assembly installation techniques.\nInstallation Instructions\nHoneywell’s written installation instructions, which are shipped with the third version of\nthe PermaLock tee assembly, describe the general requirements of the installation, but they do not\nspecify all of the necessary details to properly accomplish the installation and ensure that the\nlocking sleeve attaches to the main.\n8 Honeywell also produced an instructional video on the\ninstallation of the third version of the PermaLock tee assembly.\n9 In the video, the instructor\nexplains that using shorter wrenches allows the person installing the tee assembly to better sense\nresistance on the wrench handle during the various installation phases. The instructor further\nexplains that using longer wrenches reduces that ability to sense the various installation phases via\nthe wrench handle. However, the instructor does not specify the appropriate size of the wrench\nthat should be used. In reviewing the written instructions and the instructional video for the tee\nassembly involved in the accident, the NTSB has found that the different formats provided varying\n3 (a) Starting in 2001, the bolt material on the third version was upgraded to Nylon 11. Beginning in 2005, the\nthird version of the tee assembly was upgraded to and made of high density polyethylene. (b) Honeywell also offers\naccessories for the third version, such as stainless steel bolts and nuts for use in lieu of the Nylon bolts for tee\nassemblies installed on 1.25-inch diameter and 2-inch diameter mains.\n4 When joined together, the cutter tool and the locking sleeve are referred to as the cutter assembly.\n5 The specified length of the depth tube varies in accordance with the various tee assembly sizes.\n6 NTSB x-ray computed tomography images and post disassembly inspection of the tee assembly confirmed this\ncondition.\n7 Slow crack growth, also known as stress rupture, occurs when sustained tensile stresses in parts made from\npolymeric materials enable a network of fine craze cracks that coalesce and propagate with time, ultimately resulting\nin fracture of the part. See K. G. Budinski and M. K. Budinski, Engineering Materials: Properties and Selection,\n9th ed. (Upper Saddle River, New Jersey: Prentice Hall, 2010: 275-278).\n8 A copy of these instructions is available in the docket for the Millersville accident investigation; see the NTSB\nDocket Management System and search for accident ID DCA17FP006.\n9 The video was produced in 1996, about 1 year after Honeywell began manufacturing the third version of the tee\nassembly. A copy of the video is available in the docket for the Millersville accident investigation; see the NTSB\nDocket Management System and search for accident ID DCA17FP006.\n3\n\n<<<PAGE 4>>>\n\namounts of critical information about the installation process, which likely affected the installation\noutcomes.\nUGI Training Program\nTitle 49 Code of Federal Regulations (CFR), Part 192, Subpart N, effective October 2002,\nrequires that personnel installing mechanical tapping tee assemblies must have received\nqualification training prior to installing a tee assembly. UGI instituted a certification program for\nemployees who install mechanical tapping tee assemblies, which included a written examination\nand a practical test. However, when the tee assembly involved in the accident was installed in\n1998, federal regulations concerning operator qualification training standards for installation of\ntee assemblies did not exist, and UGI did not have a training program for installing them. At that\ntime, UGI was relying solely on the written installation instructions shipped with the tee assembly.\nNTSB Tee Assembly Installation Testing\nThe NTSB experimented with installing several exemplar PermaLock tee assemblies and\nfound the following.\nLocking Sleeve\nThe NTSB found that certain techniques can alter the tee assembly installation, particularly\naffecting whether the locking sleeve attaches to the main. For example, when the NTSB used\n4.5-inch and 7-inch length wrenches, the level of resistance was felt in the wrench handles as the\ncutter assembly was driven down the tower. Specifically, it was possible to feel the following\ninstallation stages:\n• the cutter tool piercing the main;\n• the cutter tool being driven through the wall of the main;\n• the locking sleeve forming threads into the main;\n• the outer lip portion of the locking sleeve making contact with a manufactured stop\nnear the bottom of the tower; and\n• the cutter tool separating from the locking sleeve, which was also audible.\nHowever, when using a 19-inch length wrench, changes in resistance were difficult to feel\nvia the wrench handle during the installation stages. NTSB testing demonstrated that as the cutter\nassembly was driven down the tower with the longer wrench, the outer lip portion of the locking\nsleeve was easily driven below the stop, leading to an incorrectly installed locking sleeve and\npotential damage to the threads in the main.\nSensing resistance on the handle of a wrench indicates the correct positioning of a\nPermaLock tee assembly during the installation stages. In particular, sensing that the locking\nsleeve is resting against the stop near the bottom of the tower is critical to knowing that a locking\nsleeve is properly attached to a main. Therefore, knowing which wrench length will best facilitate\nthe ability to feel increasing resistance is safety-critical information necessary to correctly\ninstalling a PermaLock tee assembly.\n4\n\n<<<PAGE 5>>>\n\nUsing the supplied depth tube is also essential to correctly installing a PermaLock tee\nassembly. The depth tube is inserted into the tower, on top of the cutter assembly. The depth tube\nprovides the installer a visual indication of the vertical travel distance of the cutter assembly,\nthereby, allowing the installer to visually verify the point at which the locking sleeve attaches to\nthe main. When the locking sleeve attaches to the main, the depth tube will be flush to 0.125 inch\nabove the top of the tower. Knowing to use the depth tube and how to use it are also critical to\nreliably ensuring the correct and safe installation of a PermaLock tee assembly.\nDetailed installation instructions for each specific tee assembly version are necessary to\neliminate confusion or misinterpretation during installation. For tee assemblies with a locking\nsleeve, such instructions must specify (1) the exact tools that are most effective for attaching a\nlocking sleeve to a main and (2) the use of a depth tube to verify that attachment. Therefore, the\nNTSB concludes that more detailed installation instructions for PermaLock mechanical tapping\ntee assemblies that specify the exact tools to be used and emphasize what should be sensed while\nusing those tools are necessary to ensure correct installation and prevent gas leaks. The NTSB\nrecommends that Honeywell update its PermaLock mechanical tapping tee assembly installation\ninstructions to specify the exact tools that should be used during installation and explain what an\ninstaller should sense while using those tools throughout the installation process. For example,\nspecify which size wrench to use when installing a PermaLock tee assembly, and explain what\nshould be sensed via the wrench handle when the locking sleeve reaches the stop at the bottom of\nthe tower indicating the locking sleeve is attached to the main.\nNylon Bolts\nAccording to a Honeywell representative, the locking sleeve is the primary means of\nsecuring a PermaLock tee assembly tower to a main. A saddle O-ring, made from an elastomer, is\nlocated under the tower of the tee assembly (see figure). When the tower is attached to the main,\nthe saddle O-ring forms a seal between the tower and the main that prevents gas from escaping out\nof the tee assembly. If the locking sleeve within the tower is not attached to the main, additional\ntensile stress is placed on the four Nylon bolts, which are used to join the tower and the base\ntogether around the outer surface of the main. The four Nylon bolts then become the fail-safe\nfeature holding the tee assembly in place. When the locking sleeve is not attached to the main,\nfracture of one or more of the Nylon bolts can be sufficient to allow a gap to open in the saddle\nO-ring area between the tower and the main where gas can escape out of the tee assembly.\nThe mechanical behavior of bolts fabricated from polymers, such as Nylon, is different\nthan metallic materials, such as stainless steel. Nylon bolts have lower tensile strength and creep\nresistance, and they are susceptible to failure by slow crack growth, a failure mode not encountered\nin traditional metal alloys (such as in the case of the bolt-joint design of the tee assembly involved\nin the Millersville accident).\n10 Honeywell tee assembly installation instructions do not warn about\nthe consequences of slow crack growth and stress relaxation due to creep, which can result from\novertightening the Nylon bolts.11 The NTSB concludes that Nylon bolts are susceptible to slow\n10 (a) Tensile strength refers to the amount of stress a material can endure before fracturing. (b) Creep is the\ndeformation of a material when exposed to constant stress for an extended period of time. Creep resistance refers to\nthe ability of a material to resist deformation when subjected to constant stress for an extended period of time.\n11 Stress relaxation is the reduction in stress in plastic material when subjected to constant strain. Deformation\ncan progress until eventual fracture of the material.\n5\n\n<<<PAGE 6>>>\n\ncrack growth when overtightened. Therefore, the NTSB recommends that Honeywell specify in\nits PermaLock mechanical tapping tee assembly installation instructions a not-to-exceed torque\nlimit for Nylon bolts and have that value checked and adjusted with a torque wrench immediately\nafter installation.\nUGI Remediation Program\nThe UGI remediation program refers to repairing or replacing PermaLock tee assemblies.\n12\nSpecifically, the UGI Gas Operations Manual, Section 70.40.20, “Remediation of Perfection\nPlastic Mechanical Tapping Tees,” states that the tee assembly Nylon bolts are subject to breaking,\nand the locking sleeve may not have attached to the main during installation.13 UGI remediation\nincludes replacing the Nylon bolts, checking the attachment of the locking sleeve to the main,\ngathering information on the tee assembly installation and site conditions, and handling any leaks\nthat have occurred.\n14\nWhen a tee assembly is excavated and found with one or more fractured Nylon bolts but\nshows no evidence of a gas leak, UGI replaces all of the Nylon bolts with type 316 stainless steel\nbolts, flat and lock washers, and nuts. When a tee assembly is found leaking gas at its base, UGI\ncuts out the segment of the main with the tee assembly and replaces it with a new main segment\nand a new approved tee assembly.\nSince 2007, UGI has remediated or replaced about 4,000 PermaLock tee assemblies, more\nthan a 1,000 of which have been remediated or replaced since the July 2, 2017, Millersville\naccident. UGI also stopped installing PermaLock tee assemblies about 10 years ago, choosing\ninstead to install electrofusion tee assemblies in their place.\n15\nRelated Incidents and Investigations\nOut of concern that incorrectly installed PermaLock tee assemblies may be a widespread\nsafety issue, the NTSB reviewed related incidents and investigations and found the following.\nUGI Excavation, 2006\nOn September 2, 2006, a natural gas explosion destroyed a residence at 39 Apple Blossom\nDrive, in West Lampeter Township, Pennsylvania. UGI excavated a PermaLock tee assembly that\nwas leaking gas from the main in front of the residence. The tee assembly had two fractured bolts.\nUGI contracted JANA Laboratories, Incorporated (JANA), to examine the tee assembly; JANA\n12 The remediation program applies to all three versions of the PermaLock tee assemblies. Because the first two\nversions of the tee assembly do not contain a locking sleeve, the position of the internal cutter tool is not checked. For\nall versions, the Nylon bolts are replaced.\n13 The UGI Gas Operations Manual became effective February 16, 2015.\n14 According to the UGI Gas Operations Manual, to determine the depth of a locking sleeve and whether it is\nattached to a m","truncated":true,"body_characters":49540}