# Pacific Gas & Electric Third-Party Line Strike and Fire - **operation:** document - **citation:** PLD19MR001 - **title:** Pacific Gas & Electric Third-Party Line Strike and Fire - **source type:** incident - **agency:** National Transportation Safety Board - **status:** current - **official:** true - **published on:** 2021-10-14 - **effective on:** 2019-02-06 - **summary:** Accident. in San Francisco, CA, USA. on 2019-02-06. Pacific Gas & Electric. Leak/explosion/fire - **machine formats:** - **json:** https://regulus.evalyn.ai/document/ntsb-case-pld19mr001.json - **markdown:** https://regulus.evalyn.ai/document/ntsb-case-pld19mr001.md - **app url:** https://regulus.evalyn.ai/document/ntsb-case-pld19mr001 - **source url:** https://www.ntsb.gov/investigations/Pages/PLD19MR001.aspx **body:** NTSB investigation PLD19MR001. Event Type: Accident Event Date: 2019-02-06 Event City: San Francisco Event State Or Region: CA Event Country: USA Pipeline Operator: Pacific Gas & Electric Pipeline Type: Distribution Accident Type: Leak/explosion/fire Completion Status: Completed Report Number: 67135 Report Date: 2021-07-27 Probable cause: The National Transportation Safety Board determines that the probable cause of the February 6, 2019 release of natural gas from a Pacific Gas & Electric distribution main and resulting fire was the failure of Kilford Engineering, Inc. to follow safe excavation practices within the tolerance zone which caused the impact of the bucket attachment of the mini excavator with the branch connection, that led to a longitudinal fracture in the 4-inch distribution main. Tier1Name: Other Tier2Name: Fire (post-release) Tier1Name: System shutdown Tier2Name: Emergency response Tier1Name: Emergency response Tier2Name: Evacuation Tier1Name: System shutdown Tier2Name: Product leak/release Tier1Name: Other Tier2Name: External/third-party damage Finding Tier1Name: Organizational Finding Tier2Name: Development Finding Tier3Name: Design Finding Modifier Name: Emergency services Finding Report Text: Organizational - Development - Design - Emergency services Finding Tier1Name: Organizational Finding Tier2Name: Support/oversight/monitoring Finding Tier3Name: Safety programs Finding Modifier Name: State/Local agency Finding Report Text: Organizational - Support/oversight/monitoring - Safety programs - State/Local agency Finding Tier1Name: Organizational Finding Tier2Name: Support/oversight/monitoring Finding Tier3Name: Enforcement Finding Modifier Name: State/Local agency Finding Report Text: Organizational - Support/oversight/monitoring - Enforcement - State/Local agency Finding Tier1Name: Personnel Finding Tier2Name: Action/decision Finding Tier3Name: Action Finding Modifier Name: Equipment/vehicle operator Finding Report Text: Personnel - Action/decision - Action - Equipment/vehicle operator Finding Tier1Name: Personnel Finding Tier2Name: Action/decision Finding Tier3Name: Information processing/decision making Finding Modifier Name: Equipment/vehicle operator Finding Report Text: Personnel - Action/decision - Information processing/decision making - Equipment/vehicle operator Finding Tier1Name: Personnel Finding Tier2Name: Action/decision Finding Tier3Name: Information processing/decision making Finding Modifier Name: Equipment/vehicle operator Finding Report Text: Personnel - Action/decision - Information processing/decision making - Equipment/vehicle operator Finding Tier1Name: Environment/Infrastructure Finding Tier2Name: Physical environment Finding Tier3Name: Vehicle/equipment operations Finding Modifier Name: Compliance w/ procedure Finding Report Text: Environment/Infrastructure - Physical environment - Vehicle/equipment operations - Compliance w/ procedure Finding Tier1Name: Environment/Infrastructure Finding Tier2Name: Operating environment/control system Finding Tier3Name: Communication system Finding Modifier Name: Availability of related info Finding Report Text: Environment/Infrastructure - Operating environment/control system - Communication system - Availability of related info Finding Tier1Name: Pipeline Finding Tier2Name: Pipline systems/equipment Finding Tier3Name: (general) Finding Modifier Name: Not specified Finding Report Text: Pipeline - Pipline systems/equipment - (general) - Not specified Finding Tier1Name: Personnel Finding Tier2Name: Experience/knowledge Finding Tier3Name: Knowledge Finding Modifier Name: Equipment/vehicle operator Finding Report Text: Personnel - Experience/knowledge - Knowledge - Equipment/vehicle operator Official NTSB investigation data. NTSB findings determine probable cause and make safety recommendations; they do not adjudicate civil liability or regulatory violations. What Happened On February 6, 2019, the excavator operator for a third-party contractor, Kilford Engineering Inc., impacted a Pacific Gas & Electric Company (PG&E) branch connection with the mini excavator trenching bucket attachment during mechanical excavation for fiberoptic conduit installation, which resulted in the release and ignition of natural gas. The accident occurred in the Richmond District, a neighborhood in San Francisco, California. A nearby restaurant with a rental unit above caught fire. There were no injuries. Estimated damages to nearby buildings and the pipeline system exceeded $10 million. The San Francisco Fire Department was dispatched and arrived on scene and focused on containing the fire and minimizing its spread while PG&E crews worked to isolate and shut down the gas pipeline line. The fire department and police department evacuated about 100 persons, and PG&E shut off natural gas service to 328 customers. At 3:36 p.m., the damaged pipelines and branch connection were isolated, and the fire department extinguished the gas fire 2 minutes later. What We Found We determined that the probable cause of the release of natural gas from the Pacific Gas & Electric Company distribution pipeline and the subsequent fire was the failure of the Kilford Engineering Inc. operator and spotter to follow safe excavation practices within the tolerance zone, which resulted in the mini excavator trenching bucket attachment impacting the branch connection. What We Recommended As a result of the investigation, we made one recommendation each to the San Francisco Police Department, Fire Department, and Department of Emergency Management and two recommendations to PG&E. PAR-21-02 <<>> Pacific Gas & Electric Third-Party Line Strike and Fire San Francisco, California February 6, 2019 Accident Report NTSB/PAR-21/02 PB2021-100925 National Transportation Safety Board <<>> NTSB/PAR-21/02 PB2021-100925 Notation 67135 Adopted July 27, 2021 Pipeline Accident Report Pacific Gas & Electric Third-Party Line Strike and Fire San Francisco, California February 6, 2019 National Transportation Safety Board 490 L’Enfant Plaza, S.W. Washington, D.C. 20594 <<>> National Transportation Safety Board. 2021. Pacific Gas & Electric Third-Party Line Strike and Fire, San Francisco, California, February 6, 2019. NTSB/PAR-21/02. Washington, DC: NTSB. Abstract: On February 6, 2019, at 1:07 p.m. local time, the excavator operator for a third-party contractor, Kilford Engineering Inc., impacted a Pacific Gas & Electric Company (PG&E) branch connection with a mini excavator trenching bucket attachment during mechanical excavation for fiberoptic conduit installation, which resulted in the release and ignition of natural gas. The accident occurred in the Richmond District of San Francisco, California. A nearby restaurant with a rental unit above caught fire. There were no injuries. Estimated damages to nearby buildings and the pipeline system exceeded $10 million. The National Transportation Safety Board (NTSB) determined that the probable cause of the accident was the failure of the Kilford operator and spotter to follow safe excavation practices within the tolerance zone, which resulted in the mini excavator trenching bucket attachment impacting the pipeline’s branch connection. The investigators focused on the safety issues of third-party excavation damage to buried natural gas pipelines, enforcement challenges of California’s damage prevention law, PG&E’s data integration gaps during the development of the valve isolation plan, and insufficient joint emergency response planning between PG&E and San Francisco emergency response agencies. As a result of the investigation, the NTSB makes one recommendation each to the San Francisco Police Department, Fire Department, and Department of Emergency Management and two recommendations to PG&E. The National Transportation Safety Board (NTSB) is an independent federal agency dedicated to promoting aviation, railroad, highway, marine, and pipeline safety. Established in 1967, the agency is mandated by Congress through the Independent Safety Board Act of 1974, to investigate transportation accidents, determine the probable causes of the accidents, issue safety recommendations, study transportation safety issues, and evaluate the safety effectiveness of government agencies involved in transportation. The NTSB makes public its actions and decisions through accident reports, safety studies, special investigation reports, safety recommendations, and statistical reviews. The NTSB does not assign fault or blame for an accident or incident; rather, as specified by NTSB regulation, “accident/incident investigations are fact-finding proceedings with no formal issues and no adverse parties … and are not conducted for the purpose of determining the rights or liabilities of any person” (Title 49 Code of Federal Regulations section 831.4). Assignment of fault or legal liability is not relevant to the NTSB’s statutory mission to improve transportation safety by investigating accidents and incidents and issuing safety recommendations. In addition, statutory language prohibits the admission into evidence or use of any part of an NTSB report related to an accident in a civil action for damages resulting from a matter mentioned in the report (Title 49 United States Code section 1154(b)). For more detailed background information on this report, visit the Accident Dockets link and search for NTSB accident ID PLD19MR001. Recent publications are available in their entirety on the NTSB website. Other information about available publications also may be obtained from the website or by contacting— National Transportation Safety Board Records Management Division, CIO-40 490 L’Enfant Plaza, SW Washington, DC 20594 (800) 877-6799 or (202) 314-6551 Copies of NTSB publications may be downloaded at no cost from the National Technical Information Service, at the National Technical Reports Library search page, using product number PB2021-100925. For additional assistance, contact— National Technical Information Service 5301 Shawnee Rd. Alexandria, VA 22312 (800) 553-6847 or (703) 605-6000 NTIS website <<>> NTSB Pipeline Accident Report Contents Contents ......................................................................................................................................i Figures ..................................................................................................................................... iii Tables........................................................................................................................................ iv Abbreviations and Acronyms ................................................................................................... v Executive Summary ................................................................................................................. vi Accident Summary ..................................................................................................................... vi Probable Cause .......................................................................................................................... vi Safety Issues .............................................................................................................................. vi Findings ....................................................................................................................................vii Recommendations ................................................................................................................... viii 1 Factual Information ............................................................................................................ 1 1.1 Accident Description ........................................................................................................... 1 1.1.1 Excavation Planning .................................................................................................. 2 1.1.2 Excavation Operation................................................................................................. 4 1.2 Response to Gas Release and Fire ........................................................................................ 8 1.2.1 San Francisco Police and Fire Department Response ................................................. 8 1.2.2 Pacific Gas & Electric Response ................................................................................ 9 1.3 PG&E Natural Gas Systems and Main Specifications ........................................................ 13 1.3.1 PG&E Overview ...................................................................................................... 13 1.3.2 Pipeline System ....................................................................................................... 14 1.3.3 Emergency Response Procedures ............................................................................. 15 1.4 Postaccident Pipeline Examination ..................................................................................... 15 1.5 Kilford Engineering ........................................................................................................... 19 1.5.1 Licensing ................................................................................................................. 19 1.5.2 Safety Procedures .................................................................................................... 20 1.5.3 Postaccident interviews with Kilford’s Mini Excavator Operator ............................. 21 1.5.4 Past Incident ............................................................................................................ 21 1.6 California Damage Prevention Regulations ........................................................................ 22 1.6.1 Excavation Regulations............................................................................................ 22 1.6.2 California Public Utilities Commission .................................................................... 22 1.6.3 Contractors State License Board .............................................................................. 23 1.6.4 California Underground Facilities Safe Excavation Board ........................................ 24 1.6.5 Damage Prevention Program Evaluation .................................................................. 25 2 Analysis .............................................................................................................................. 26 2.1 Introduction ....................................................................................................................... 26 2.2 Exclusions ......................................................................................................................... 26 2.3 Third-Party Excavation Damage ........................................................................................ 27 2.3.1 Kilford Engineering Inc. .......................................................................................... 27i <<>> NTSB Pipeline Accident Report 2.3.2 Enforcement Challenges of California Damage Prevention Law .............................. 29 2.4 Data Integration and Emergency Response ........................................................................ 30 2.5 Coordination of Emergency Response ................................................................................ 30 3 Conclusions ........................................................................................................................ 32 3.1 Findings ............................................................................................................................. 32 3.2 Probable Cause .................................................................................................................. 32 4 Recommendations ............................................................................................................. 34 Appendix A: Investigation ...................................................................................................... 35 Appendix B: Consolidated Recommendation Information ................................................... 36 References................................................................................................................................ 38 ii <<>> NTSB Pipeline Accident Report Figures Figure 1. Northwest-facing view of fire during emergency response. ..........................................2 Figure 2 Kilford’s project area. ...................................................................................................3 Figure 3. One-call street markings at northwest corner of Parker Ave. and Geary Blvd. ..............4 Figure 4. Excavation work plan on the day of the accident. ........................................................5 Figure 5. Mini excavator in storage postaccident. .......................................................................6 Figure 6. Trench depth comparisons. ..........................................................................................7 Figure 7. Postfire south-facing view of trench and excavator on Parker Ave. ..............................8 Figure 8. Map of location of gas pipelines affected the accident. .............................................. 11 Figure 9. Final valve isolation plan with valves closed and location of damage......................... 12 Figure 10. Postaccident 2-inch pipeline, 4-inch pipeline, branch connection, and cutter insert .16 Figure 11. Close-up view of bend area in 2-inch pipeline. ........................................................ 17 Figure 12. Side view of cutter insert showing diagonal gouge. .................................................. 18 Figure 13. View of fracture area in the 4-inch pipeline. ............................................................ 19 iii <<>> NTSB Pipeline Accident Report Tables Table 1. Valve isolation plan (VIP) development timeline for February 6, 2019. ...................... 12 Table 2. Valve closure times. .................................................................................................... 13 Table 3. Timeline of emergency response events. ..................................................................... 13 Table 4. Specifications for pipelines involved in accident. ........................................................ 14 Table 5. Laboratory-measured pipeline dimensions. ................................................................. 16 iv <<>> NTSB Pipeline Accident Report Abbreviations and Acronyms 911 dispatch Department of Emergency Management Public Safety Dispatch Center CFR Code of Federal Regulations CGA Common Ground Alliance CPUC California Public Utilities Commission CSLB Contractors State License Board Dig Safe Board California Underground Facilities Safe Excavation Board GDCC Gas Distribution Control Center GIS geographic information system GM&C Gas Maintenance and Construction GOV State of California Government Code GPOM Gas Pipeline Operations and Maintenance GSP gas system planning IC incident commander NOPV Notice of Probable Violation NTSB National Transportation Safety Board OSHA Occupational Safety and Health Administration PG&E Pacific Gas & Electric Company PHMSA Pipeline and Hazardous Materials Safety Administration SFDEM San Francisco Department of Emergency Management SFFD San Francisco Fire Department SFPD San Francisco Police Department USC United States Code VIP valve isolation plan v <<>> NTSB Pipeline Accident Report Executive Summary Accident Summary On February 6, 2019, at 1:07 p.m. local time, the excavator operator for a third-party contractor, Kilford Engineering Inc., impacted a Pacific Gas & Electric Company (PG&E) branch connection with the mini excavator trenching bucket attachment during mechanical excavation for fiberoptic conduit installation, which resulted in the release and ignition of natural gas. The accident occurred in the Richmond District, a neighborhood in San Francisco, California. A nearby restaurant with a rental unit above caught fire. There were no injuries. Estimated damages to nearby buildings and the pipeline system exceeded $10 million. At 1:09 p.m., the San Francisco Fire Department was dispatched and arrived on scene at 1:12 p.m. The fire department focused on containing the fire and minimizing its spread while PG&E crews worked to isolate and shut down the gas pipeline line. The fire department and police department evacuated about 100 persons, and PG&E shut off natural gas service to 328 customers. At 3:36 p.m., the damaged pipelines and branch connection were isolated, and the fire department extinguished the gas fire 2 minutes later.1 Probable Cause The National Transportation Safety Board determines that the probable cause of the February 6, 2019, release of natural gas from the Pacific Gas & Electric Company distribution pipeline and the subsequent fire was the failure of the Kilford Engineering Inc. operator and spotter to follow safe excavation practices within the tolerance zone, which resulted in the mini excavator trenching bucket attachment impacting the pipeline’s branch connection. Safety Issues This report focuses on the following safety issues: • Third-party excavation damage to buried natural gas pipelines. Third-party excavation damage is the number one cause of pipeline accidents. In this case, Kilford failed to follow safe excavation practices within the tolerance zone of the existing underground utilities by mechanically excavating near the gas pipeline. • Enforcement challenges of California’s damage prevention law. At the time of the accident, California did not have an operational damage prevention enforcement program in place; the program became operational in July 2020. Enforcement has been shown to be 1 For more information, see the factual information and analysis sections of this report. Additional information can be found in the public docket for this National Transportation Safety Board (NTSB) accident investigation (accident number PLD19MR001) by accessing the Accident Dockets link at www.ntsb.gov. For information about our safety recommendations, see the Safety Recommendation Database at the same website. vi <<>> NTSB Pipeline Accident Report the strongest method of preventing damage to buried utilities. Kilford had previously damaged an underground utility during excavation; however, because California’s damage prevention enforcement program was not yet in place, no actions were taken against the company. On January 26, 2021, the Pipeline and Hazardous Materials Safety Administration changed its evaluation of the state of California’s damage prevention enforcement program from inadequate to adequate. • PG&E’s data integration gaps during the development of the VIP. A critical part of any emergency response to a natural gas distribution incident is the development of a valve isolation plan, which is used by field personnel to isolate a damaged portion of pipeline and stop the release of gas. Any delays in the creation of such a plan can result more gas release and greater impact to customers. In this accident, it took PG&E about an hour to identify the specific locations of the valves that needed to be isolated. • Insufficient joint emergency response planning between PG&E and San Francisco, California, emergency response agencies. During the emergency response, an important piece of equipment needed to isolate a gas supply pipeline was delayed en route to the accident scene. While it ultimately did not affect the overall response, such delays in the event of a gas release could have negative impacts. By coordinating with emergency response agencies, such delays could be reduced or eliminated. Findings • The following factors did not contribute to the cause of the accident: two one-call ticket requests, locate and mark activities, and California regulations regarding the tolerance zone. Further, Pacific Gas & Electric Company’s pipeline was intact and operating as designed prior to the accident. • Natural gas facilities were accurately marked, and Kilford Engineering Inc. employees working at the site were aware of the markings indicating the locations of the 4-inch gas pipeline, 2-inch gas pipeline, and branch connection before the start of excavation. • Kilford Engineering Inc. did not follow safe excavation practices when it mechanically excavated within the tolerance zone, resulting in the Kilford Engineering Inc. operator impacting the 2-inch branch connection with the mini excavator trenching bucket, causing the release of natural gas. • Because California did not have an excavation damage enforcement program at the time of the water line strike, the state missed an opportunity to identify and deter poor safety activities presented by a new contractor. • Although sufficient data are not yet available to determine if the California Underground Facilities Safe Excavation Board’s enforcement actions have been effective in deterring future damage, enforcement is a step in the right direction for preventing third party damage to buried utilities. vii <<>> NTSB Pipeline Accident Report • Had Pacific Gas & Electric Company incorporated geographic information system location data into the software program used to develop its valve isolation plan prior to this accident, it would have reduced the time to isolate the natural gas release. • Pacific Gas & Electric Company did not follow its own procedures regarding requests for police escorts, which may have delayed the arrival of Pacific Gas & Electric Company personnel on scene during the emergency response. • While the lack of a memorandum of understanding with the San Francisco Department of Emergency Management, San Francisco Police Department, or San Francisco Fire Department addressing emergency response plans did not affect the timeliness of the Pacific Gas & Electric Company shutting off the flow of gas in this accident, it could potentially affect other responses where the squeeze-off point is accessible and/or the valve locations are readily known. Recommendations To the San Francisco Police Department, San Francisco Fire Department, and San Francisco Department of Emergency Management: Work with Pacific Gas & Electric Company to establish an agreement to provide a coordinated response and reduce response times for Pacific Gas & Electric Company’s crews to arrive at the scene of a pipeline accident. (P-21-15) To Pacific Gas & Electric Company: In collaboration with the San Francisco Police Department, San Francisco Fire Department, and the San Francisco Department of Emergency Management, establish an agreement to provide a coordinated response and reduce response times for your crews to arrive at the scene of a pipeline accident. (P-21-16) Complete the integration of detailed location data into your hydraulic modeling software so that this information is readily available for all system assets when developing a valve isolation plan. (P-21-17) viii <<>> NTSB Pipeline Accident Report 1 Factual Information 1.1 Accident Description On February 6, 2019, Kilford Engineering Inc. (Kilford), a third-party contractor, was excavating a trench to install fiberoptic conduit at the intersection of Geary Boulevard and Parker Avenue in San Francisco, California.1 During mechanical excavation, at 1:07 p.m., the operator of a mini excavator impacted a Pacific Gas & Electric Company (PG&E) branch connection between a 4-inch natural gas distribution pipeline and a 2-inch natural gas pipeline with the mini excavator’s trenching bucket.2 Shortly after the branch connection was damaged, the releasing gas ignited, resulting in structure fires in several surrounding buildings. (See figure 1.) The damaged segment was isolated at 3:36 p.m., and the structure fires were contained at 4:24 p.m. No injuries occurred as a result of this accident. 3 1 A third-party contractor is a contractor who performs excavation work independently of natural gas companies. For more information on third-party contractors and third-party damage, see the analysis section of this report. 2 All times in this report are in local time. 3 For more information, see the factual information and analysis sections of this report. Additional information can be found in the public docket for this National Transportation Safety Board (NTSB) accident investigation (accident number PLD19MR001) by accessing the Accident Dockets link at www.ntsb.gov. For information about our safety recommendations, see the Safety Recommendation Database at the same website. 1 <<>> NTSB Pipeline Accident Report Figure 1. Northwest-facing view of fire during emergency response. (Photo courtesy of PG&E.) 1.1.1 Excavation Planning Through multiple subcontracts, Kilford was hired to conduct excavation work and install conduit for fiberoptic cabling for Verizon along Geary Boulevard in San Francisco. (See section 1.5 for more information about Kilford.) The project extended from 3310 Geary Boulevard to the intersection of Geary Boulevard and Masonic Avenue, and the trench excavation was in the northernmost lane of Geary Boulevard. (See figure 2.) The project was segmented into 13 subprojects, each about one-half block long. The first segment was from 3310 Geary Boulevard to the intersection of Geary Boulevard and Parker Avenue. 2 <<>> NTSB Pipeline Accident Report Figure 2 Kilford’s project area. The scope of work called for 1,888 feet of trench excavation and the installation of 3,798 feet of 2-inch high-density polyethylene conduit inside 4-inch polyvinyl chloride piping at a depth of 36 inches. As part of the work, Kilford was responsible for maintaining a minimum of 24 inches of separation from existing utilities and for determining the location and depth of the existing utilities. In preparation for excavation, Kilford placed a “one-call” ticket on January 21, 2019, to request the location and marking of buried utilities within the project area. 4 Information from the January 21, 2019, one-call ticket indicated that a PG&E representative called the Kilford employee listed as the contact to clarify the excavation location because Kilford did not provide a complete location on the tickets. Kilford submitted a second ticket on January 22, 2019 in an effort to address the issue. PG&E located and marked its natural gas utilities within the requested area on January 28 and 29, 2019. The depths of the utilities were not marked (nor were they required to be marked. (See section 1.6.1 for more information.) Figure 3 shows the one-call markings at the intersection of Geary Boulevard and Parker Avenue before excavation. 4 One-call is the phone number (811) to call to request a location of all buried utilities in the area where excavation is to occur. Title 49 Code of Federal Regulations (CFR) 192.614 requires pipeline operators to participate in a one- call center and provide locate-and-mark services to excavators that notify the operator of any planned excavation work in the region of their utilities. Excavators call 811 and place a ticket, known as a one-call ticket, which is used to track the locate-and-mark activities of the various owners of the buried utilities. In the state of California, this one-call ticket can be accessed online by the excavator and the utilities. 3 <<>> NTSB Pipeline Accident Report Figure 3. One-call street markings at northwest corner of Parker Ave. and Geary Blvd. (Photo Courtesy of PG&E.) Note: The buried gas utilities are marked in yellow. A green circle has been placed on the figure to indicate the location of the branch connection that was ultimately struck. 1.1.2 Excavation Operation On February 4 and 5, 2019, the asphalt on the roadway was cut in the area where the excavation work was to be performed; Kilford began the asphalt removal and excavation work on February 6, 2019, and five Kilford employees were on site to perform the work. Kilford employees arrived at the site about 7:30 a.m. and held a safety briefing where they discussed topics such as personal protective equipment, finding buried utilities, and damage to tools. Excavation work began about 9:00 a.m., once traffic control was in place. 5 The work plan for that day was for three lines of conduit to be placed along Geary Boulevard 50 feet west of the intersection with Parker Avenue at a new handhole and run to the intersection where one of the three lines of conduit would then run north along Parker Avenue to a telecommunications (telecom) pole. (See figure 4.) 5 Traffic control was performed by two employees of City Rise Safety and Services Traffic Control. 4 <<>> NTSB Pipeline Accident Report Figure 4. Excavation work plan on the day of the accident. According to the job foreman, he began work by breaking up and removing the asphalt road top with a skid steer while the other employees used hand shovels.6 After the asphalt road top was removed, the job foreman (mini excavator operator) used a mini excavator to excavate the trenches.7 (See figure 5.) While using the mini excavator, he relied on a spotter to help locate utilities. 8 The spotter determines the depth of underground utilities and performs other safety tasks, such as keeping the operator aware of personnel in the area or other hazards because of the limited view from inside the mini excavator (CGA 2018). 6 (a) A skid steer is a small engine-powered machine with a front loader and four wheels or two tracks that is commonly used for heavy excavation work such as breaking up and removing concrete. (b) State of California Government Code (GOV) 4216.4(a)(2)(B) states a person performing excavation work may use power-operated equipment for the removal of pavement if there are no known utilities within such pavement. 7 A mini excavator is a small engine-powered machine used for finer excavation work such as trenching. For the majority of its mechanical excavation activities, Kilford used a 2018 CAT 305E2 CR mini excavator. The attached trenching bucket had three teeth that were connected via a 3-inch-wide welded bar. 8 Common Ground Alliance’s (CGA) Best Practices Guide recommends the contractor have an observer to assist the operator of the excavator when operating around underground utilities; this person is often referred to as a spotter (CGA 2018). 5 <<>> NTSB Pipeline Accident Report 3-inch wide welded bar Trenching bucket Figure 5. Mini excavator in storage postaccident. Excavation began in front of 3310 Geary Boulevard using a combination of hand digging with shovels and mechanical excavation using the trenching bucket attachment on the mini excavator. Excavation continued along Geary Boulevard to Parker Avenue; then the mini excavator operator and spotter started digging at the telecom pole on Parker Avenue working south toward the intersection. The operator then moved the mini excavator to Geary Boulevard and began digging to join the two trenches together. The spotter was in the Parker Ave. trench at that time. The other three employees began to install conduit along Geary Boulevard in the first trench. The operator stated that they had previously located the 4-inch gas pipeline and the 2-inch gas pipeline at 48 inches depth. The operator stated that they only exposed a portion of each pipeline and did not expose the branch connection where the two pipelines met. He stated that he was digging at least 2 to 3 feet from the 2-inch gas pipeline that had been exposed along Parker and was likely higher than the 2-inch gas pipeline; he reported that he was about 4 feet from where the spotter exposed the 4-inch gas pipeline along Geary Avenue. The spotter reported that he could not see either of the gas pipelines (he never saw the yellow plastic of the pipelines) in the trench, although he could see an electrical conduit and a metal line. He also stated that the mini excavator bucket was about 2 feet south of where the gas pipeline was. The operator also reported that he decided to dig to 30 inches, even though the scope of work called for 36-inch trench depth. The spotter reported that the trench was only 24 to 30 inches deep where the mini excavator was working at the intersection. (See figure 6.) 6 <<>> NTSB Pipeline Accident Report Figure 6. Trench depth comparisons. As the operator continued to remove dirt with the mini excavator, the gas started to escape; he did not notice an impact or scraping before the gas release. Once the release began, the spotter immediately climbed out of the trench and ran north, away from the release site. The operator got out of the excavator as the spotter exited the trench. As the operator was returning to the excavator to retrieve his phone, the gas ignited. 7 <<>> NTSB Pipeline Accident Report Figure 7. Postfire south-facing view of trench and excavator on Parker Ave. (Photo courtesy of PG&E) Note: Figure 7 shows the mini excavator as found after the fire was extinguished. Once the gas ignited, the flames, which extended above the height of a 2-story building, impinged on a nearby, fully occupied restaurant at 3300 Geary Boulevard. This caused a structure fire at the restaurant. Employees and customers self-evacuated immediately. Later, the fire spread to neighboring buildings, causing smaller structure fires at 3308, 3310, and 3250 Geary Boulevard. 1.2 Response to Gas Release and Fire 1.2.1 San Francisco Police and Fire Department Response At 1:08 p.m., the San Francisco Department of Emergency Management (SFDEM) Public Safety Dispatch Center (911 dispatch) received multiple calls from the public reporting a fire and possible explosion at the intersection of Geary Boulevard and Parker Avenue. San Francisco Police Department (SFPD) officers were first on scene at 1:09 p.m. and began performing evacuations and controlling traffic. San Francisco Fire Department (SFFD) Battalion 7, Engine 10, and Truck 10 were dispatched to the scene at 1:09 p.m., were en route within 1 minute, and were on scene by 1:12 p.m. The Battalion 7 chief designated the event a 8 <<>> NTSB Pipeline Accident Report working fire with a gas explosion and assigned it as a first-alarm fire.9 An SFFD assistant chief was dispatched at 1:17 p.m. and assumed command as the SFFD incident commander (IC) while en route. An additional battalion, three more engines, and one truck were also dispatched at that time. As the SFFD IC approached the site, he could see flames from three blocks away, so he upgraded the response to a second-alarm fire at 1:20 p.m. as he was en route. An additional two battalions, four engines, and one truck were dispatched in response to the second-alarm designation. When the SFFD IC arrived at 1:22 p.m., he recognized that the SFFD was not going to be able to put out the gas fire. SFFD procedures for Class 2 flammable gases stated that gas-based fires were not to be put out unless the gas has first been shut off. Instead, the fire had to be contained and surrounded until the fuel source was removed. The SFFD IC deployed four battalions around the fire to keep it contained until the gas release was isolated. The SFFD IC declared a third alarm at 1:36 p.m., and two additional battalions, four engines, and two trucks were dispatched at that time. After the fire was extinguished, an additional engine was dispatched to monitor for possible rekindling. In addition to the restaurant, all buildings within a half-block radius of the restaurant fire as well as an extra half block to the north were cleared as fully evacuated at 1:56 p.m. SFPD controlled public access to the active fire area by blocking the main and side streets for a 4-block radius centered on 3300 Geary B - **truncated:** true - **body characters:** 111147