# NTSB Safety Recommendation P-22-002 - **operation:** document - **citation:** P-22-002 - **title:** NTSB Safety Recommendation P-22-002 - **source type:** guidance - **agency:** National Transportation Safety Board - **status:** guidance - **official:** true - **published on:** 2022-09-14 - **effective on:** 2022-09-14 - **summary:** TO THE PIPELINE AND HAZARDOUS MATERIALS SAFETY ADMINISTRATION: Advise natural gas transmission pipeline operators on a) the circumstances of this accident; b) the need to evaluate the risks associated with flow reversal projects; and c) the impacts of such projects on hydrogen-induced cracking. - **machine formats:** - **json:** https://regulus.evalyn.ai/document/ntsb-recommendation-p-22-002.json - **markdown:** https://regulus.evalyn.ai/document/ntsb-recommendation-p-22-002.md - **app url:** https://regulus.evalyn.ai/document/ntsb-recommendation-p-22-002 - **source url:** https://data.ntsb.gov/carol-main-public/sr-details/P-22-002 **body:** NTSB safety recommendation P-22-002. TO THE PIPELINE AND HAZARDOUS MATERIALS SAFETY ADMINISTRATION: Advise natural gas transmission pipeline operators on a) the circumstances of this accident; b) the need to evaluate the risks associated with flow reversal projects; and c) the impacts of such projects on hydrogen-induced cracking. Priority: CLASS II Overall Status: Closed - Acceptable Action Issued Date: 2022-09-14 Adopted Date: 2022-08-15 Overall Date Closed: 2025-06-16 Synopsis: On August 1, 2019, at 1:23 a.m. local time, an Enbridge Inc. (Enbridge) 30-inch natural gas transmission pipeline ruptured in Danville, Kentucky, releasing about 101.5 million cubic feet of natural gas that ignited. The accident resulted in 1 fatality, 6 injuries, and the evacuation of over 75 individuals in the Indian Camp Subdivision. Five residences were destroyed by resulting structure fires, and an additional fourteen were damaged. A nearby railroad track was also damaged, and over 30 acres of land were burned. Probable Cause: The National Transportation Safety Board determines that the probable cause of the August 1, 2019, rupture of an Enbridge Inc. natural gas transmission pipeline and resulting fire was hydrogen-induced cracking at the surface of Line 15 in an area of damaged coal tar enamel coating resulting from a 2014 gas flow reversal project that increased corrosion rates and hydrogen generation. Contributing to this accident was Enbridge’s integrity management program, which did not accurately assess the integrity of the pipeline or estimate the risk from interacting threats. Ntsbnumber: PLD19FR002 Report Number: PIR-22-02 Addressee Name: PHMSA Addressee Status: Closed - Acceptable Action Addressee Date Closed: 2025-06-16 Addressee Acronym: PHMSA Addressee Organization Type: G-Federal Government Communication Date: 2022-09-14 Communication Type: Transmittal Letter Communication Contents: This letter provides information about the National Transportation Safety Board’s (NTSB) August 15, 2022, report Enbridge Inc. Natural Gas Transmission Pipeline Rupture and Fire, Danville, Kentucky, August 1, 2019, NTSB/PIR-22/02. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Nonconservative assumptions used to calculate potential impact radius. • Incomplete evaluation of the risks caused by a change of gas flow direction. • Limitations in data analysis related to the 2011 in-line inspection. • Operators’ potential for incomplete assessment of threats and threat interactions. • Missed opportunities in training and requalification practices at Enbridge. Accordingly, the NTSB makes the following safety recommendations to the Pipeline and Hazardous Materials Safety Administration. Additional information regarding these recommendations can be found in the noted sections of the report. • Revise the calculation methodology used in your regulations to determine the potential impact radius of a pipeline rupture based on the accident data and human response data discussed in this report. (P-22-1) (See section 2.3) • Advise natural gas transmission pipeline operators on (a) the circumstances of this accident; (b) the need to evaluate the risks associated with flow reversal projects; and (c) the impacts of such projects on hydrogen-induced cracking. (P-22-2) (See section 2.4) • Advise natural gas transmission pipeline operators of the possible data limitations associated with hard spot magnetic flux leakage in-line inspection tools and analyses used in hard spot management programs and reinforce the need to follow industry best practices when conducting in-line inspection data analysis. (P-22-3) (See section 2.5) The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendations by number (Safety Recommendations P-22-1, -2 and -3). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From pipeline investigation report (PIR-22-02), "Enbridge Inc. Natural Gas Transmission Pipeline Rupture and Fire, Danville, Kentucky, August 1, 2019." Published on September 14, 2022. 2.4 Management of Gas Flow Reversal As stated previously, because the pipe was under cathodic protection following the gas flow reversal, areas with coating defects had increased hydrogen evolution, which reduced the pipeline integrity. However, after the gas flow reversal in 2014, neither Spectra nor Enbridge evaluated the data available on temperatures, cathodic protection, and external corrosion anomalies in L15 VS4 to determine the impacts of the project on pipeline integrity. These data are difficult to predict in advance, and cathodic protection may not respond to operational changes in a predictable way. Extensive research on the effects of major operational changes has not been performed, leaving operators only able to plan for general effects (for example, adding gas coolers to address increased temperatures) and requiring them to perform further study after operational changes to detect more subtle effects (such as unstable or ineffective cathodic protection leading to hydrogen evolution). Because Enbridge and its predecessor did not review critical data, they did not identify the suitability of its corrosion control equipment and infrastructure for reversed flow, recognize indicators of coating damage, or identify the cathodic protection system as a likely source of hydrogen evolution. The NTSB concludes that Enbridge and Spectra did not effectively identify, investigate, or manage the impact of the gas flow reversal project on the level of hydrogen evolution in the pipeline surface, which ultimately contributed to the failure of the pipeline. Therefore, the NTSB recommends that Enbridge evaluate the effectiveness of its corrosion control equipment and infrastructure following any major change in operations, such as a gas flow reversal. The NTSB further concludes that comprehensive management of the changes resulting from the gas flow reversal project on Line 15 would have identified and addressed risks such as coating damage, ineffective cathodic protection, and suitability of corrosion control equipment and infrastructure that led to hydrogen-induced cracking in the pipeline surface. Therefore, the NTSB recommends that PHMSA advise natural gas transmission pipeline operators on a) the circumstances of this accident; b) the need to evaluate the risks associated with flow reversal projects; and c) the impacts of such projects on hydrogen-induced cracking. Addressee Acronym: PHMSA Addressee Organization Type: G-Federal Government Communication Date: 2023-01-11 Communication Type: Official Correspondence Communication Contents: We are aware that you discussed this recommendation with pipeline operators during your December 13–15, 2022, public meeting in Houston, Texas. Additionally, we note that you plan to update the advisory bulletin for flow reversal (ADB-2014-04). Pending your update of this ADB, including adding the need to evaluate the risks associated with flow reversal projects and the impacts of such projects on hydrogen-induced cracking, Safety Recommendation P-22-2 is classified OPEN-- ACCEPTABLE RESPONSE. Addressee Acronym: PHMSA Addressee Organization Type: G-Federal Government Communication Date: 2025-06-16 Communication Type: Official Correspondence Communication Contents: We commend PHMSA for hosting the December 13–15, 2022, public meeting in Houston, Texas, focusing on these recommendations. National Transportation Safety Board (NTSB) staff presented at this meeting, and other NTSB staff attended to listen to public input on these recommendations. At the public meeting, PHMSA staff said the agency planned to consider updating the advisory bulletin for flow reversal (ADB-2014-04); however, you ultimately decided PHMSA will not be issuing an updated advisory bulletin. Although an updated advisory bulletin would have been appreciated, it is not needed to meet the intent of this recommendation. Attendees at the meeting were advised that notification is required for flow reversal projects, conversion of service, or change in commodity. Furthermore, a 2017 amendment to ADB-2014-04 addresses several factors that operators should consider when completing flow reversal projects, including the potential impacts on integrity management programs. This action meets the intent of this recommendation. Accordingly, the Board has classified Safety Recommendation P-22-2 CLOSED-- ACCEPTABLE ACTION. Addressee Acronym: PHMSA Addressee Organization Type: G-Federal Government Communication Date: 2025-01-17 Communication Type: Official Correspondence Communication Contents: -From Tristan H. Brown, Deputy Administrator: PHMSA’s Actions to Address Safety Recommendations P-22-002 and P-22-003: Following the NTSB investigation into the Danville incident and recommendations, PHMSA responded to the NTSB in correspondence dated November 25, 2022, for Recommendations P-22-002 and P-22-003. PHMSA reviewed incident and accident data and available information regarding hard spots and the appropriate methodologies and technologies for detecting them. PHMSA met with industry and technology companies to gather information regarding hard spot management programs and appropriate in-line inspection (ILI) technologies for detection and evaluation of different anomalies, including hard spots. PHMSA hosted a three-day public meeting in Houston, Texas, in December 2022. The Agency provided an overview of the Danville incident and the NTSB’s findings and recommendations in PIR-22-02, and invited stakeholders to present information related to hard spot detection methodologies. Subsequently, PHMSA identified more pipe manufacturers and pipe vintages that could have issues with hard spots. As a result, on November 18, 2024, PHMSA published Advisory Bulletin ADB-2024-011 (ADB) titled, Identification and Evaluation of Potential Hard Spots – In-line Inspection Tools and Analysis. In this ADB, PHMSA alerted operators of advancements in knowledge of hard spot susceptibility to include multiple pipe manufacturers and manufacturing years; hydrogen-induced cracking; new developments in ILI technologies to better identify features associated with hard spots; significant improvements in data analytic methods to enable older data to be re-analyzed to identify previously unknown features; and information stating that data verification should not be limited in scope and should include a thorough review of all relevant data. PHMSA also detailed actions pipeline operators should consider taking to ensure pipeline safety, including review of pipeline design and construction records to determine hard-spot susceptibility; review of known integrity issues; development and implementation of enhanced assessment approaches to material hardness anomaly validations; re-evaluation of existing ILI data; and publicly sharing findings. The scope of the ADB included owners and operators of gas, hazardous liquid, and carbon dioxide pipeline systems—beyond the original scope of the NTSB’s recommendations. PHMSA’s Actions to Address Safety Recommendation P-22-002: By correspondence dated January 11, 2023, the NTSB classified this Safety Recommendation as “Open – Acceptable Response” pending PHMSA’s update of the advisory bulletin for flow reversal (ADB-2014-04). While PHMSA initially considered an update of ADB-2014-04, the safety objectives of P-22-002 were achieved through multiple complementary actions to ADB 2014-04 and the requirements of existing regulations. These actions include direct engagement with pipeline operators at our December 2022 public meeting where we discussed the Danville incident findings, the need for the recently issued ADB-2024-01, and our past and on-going research & development (R&D) in this and related area. The pipeline safety regulationsi in Title 49 Code of Federal Regulations (CFR) Parts 190–199 require natural gas transmission pipeline operators to assess and manage hard spots both within and outside of high consequence areas (§ 192.710, § 192.921(a), and § 192.937(c)). These regulations also require notification of flow reversals expected to last more than 30 days (§ 191.22(c)(1)(v)); require integrity assessment methods capable of detecting susceptible hard spots with cracking (§ 192.710, § 192.921(a), and § 192.937(c)); and specify evaluation and remediation of crack or crack-like defects (§ 192.917(e)(6)). The regulations also require controlling the amount of cathodic protection to prevent coating or pipe damage (§ 192.463(c)) and prescribe requirements for threat identification risk analysis (§ 192.917). Operators must integrate pertinent information including from operations and maintenance activities; manufacturer and manufacture dates; the existence of disbonded coatings or other conditions that compromise the effectiveness of corrosion protection; and industry experience for incident, leak, and failure history (§ 192.917(b)). Additionally, operators subject to integrity management requirements must implement measures beyond those specifically prescribed in the regulations to prevent and mitigate the consequence of pipeline failure in high consequence areas. As preventative and mitigative measures, operators must consider, among others, establishing and implementing adequate operation and maintenance processes that could enhance safety; re-coating damaged/disbonded coating; and testing to determine unknown material mechanical properties to ensure or substantiate maximum allowable operating pressure (§ 192.935). ADB 2014-04 and its corresponding supplementary guidance document specifically address reviewing past integrity assessments, noting that threat locations may change and previously stable threats may become unstable due to operational changes. The ADB stated that it may not be advisable to perform flow reversals on pipelines with history of failures, leaks, or manufacturing defects. PHMSA’s recent ADB 2024-01 expands on ADB 2014-04 by alerting operators of advancements in knowledge of hard spot susceptibility across multiple pipe manufacturers and manufacture years; hydrogen-induced cracking; new developments in ILI technologies and data analytics; and specific actions operators should take to ensure pipeline safety. In a December 2022 public meeting, PHMSA also highlighted the January 2017 amendments to the pipeline safety regulations requiring notifications of flow reversals, conversions to service, and changes in commodity. Meeting materials may be found on PHMSA’s website. PHMSA’s review of incident and accident reports from August 15, 2022—the date P-22-002 was issued—through December 2024 did not identify any incidents or accidents where flow reversal or hydrogen-induced cracking was causal or the apparent cause to the incident or accident. REQUEST FOR CLOSURE OF RECOMMENDATIONS P-22-002 AND P-22-003: PHMSA takes its responsibility to fully address all NTSB recommendations seriously and works hard to continuously improve its pipeline safety program. Based on the actions PHMSA has taken, I am requesting that Safety Recommendations P-22-002 and P-22-003 be classified as “Closed-Acceptable Action.” PHMSA looks forward to working with your office as it continues to strive to ensure the safe, reliable, and environmentally sound operation of the nation’s pipeline transportation system. If you have any questions or require additional information, please do not hesitate to contact me, or have your staff contact Damon Hill, Deputy Director of Governmental, International, and Public Affairs. Addressee Acronym: PHMSA Addressee Organization Type: G-Federal Government Communication Date: 2022-11-25 Communication Type: Official Correspondence Communication Contents: -From Tristan H. Brown, Deputy Administrator, PHMSA: Concur. PHMSA will update the advisory bulletin for flow reversal (ADB-2014-04) to include any lessons learned since the advisory bulletin was published in September 2014 and provide additional considerations regarding the potential impacts of flow reversals on hydrogen-induced cracking. PHMSA also plans to present and discuss the circumstances of this accident at the December public meeting in Houston, Texas. PHMSA continually seeks to use and evolve its oversight program, including changes to pipeline safety policies and inspection and enforcement approaches. A major tenet of PHMSA’s oversight program is that pipeline operators must know and understand their pipeline systems and use appropriate technologies and procedures to address risk to prevent pipeline failures while considering the inherent limitations of technology. PHMSA prescribes factors that must be addressed to mitigate risk and conducts inspections to ensure adequate measures are carried out effectively. PHMSA also invests in research and development that advances the best expertise in the world to help improve technology, especially detection methods relevant to pipeline failures. PHMSA is fully committed to carrying out its pipeline safety oversight authority to improve safety and protect Americans while addressing all of the NTSB safety recommendations. PHMSA also values the role of the NTSB and our collective pipeline safety partnership. We believe the planned actions described above will adequately address the safety recommendations and we look forward to working with you and the dedicated staff at the NTSB as we continue our important work to help ensure the safe, reliable, and environmentally sound operation of the nation’s pipeline transportation system. - **truncated:** false - **body characters:** 18262