NTSB Safety Recommendation P-22-001

NTSB safety recommendation P-22-001.

TO THE PIPELINE AND HAZARDOUS MATERIALS SAFETY ADMINISTRATION: 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.

Priority: CLASS II

Overall Status: Open - Acceptable Response

Issued Date: 2022-09-14

Adopted Date: 2022-08-15

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: Open - Acceptable Response

Addressee Acronym: PHMSA

Addressee Organization Type: G-Federal Government

Communication Date: 2023-05-01

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-23-01 “Kinder Morgan Natural Gas–Fueled Explosion, Coolidge, Arizona, August 15, 2021,” published on May 1, 2023: 2. Analysis In this accident, a Kinder Morgan natural gas pipeline ruptured in rural Coolidge, Arizona, destroying a nearby farmhouse and killing two of its three occupants. A segment of the pipe was ejected in the rupture. NTSB investigators conducted metallurgical testing of the ejected pipe segment and found longitudinal surface breaking cracks, evidence of high pH SCC, in three regions at the toe of the ejected pipe segment’s longitudinal seam weld. Pitting corrosion observed on the surface of the tested pipe pieces indicated that moisture had settled on the pipe surface, likely due to tenting of the spiral wrap tape coating at the gap between the coating and where the weld meets the pipe surface. The tape coating had most likely shielded the toe of the weld from cathodic protection, allowing the toe of the weld to corrode from SCC. Over time, the three SCC regions had spread, eventually connecting into one larger fracture, which split open the pipeline on August 15, 2021. Kinder Morgan had voluntarily included the segment of Line 2000 that ruptured in its integrity management program and subsequently conducted risk assessments on the accident segment. However, the data on coating type on the accident pipeline segment, recorded in PODs and used in Kinder Morgan’s risk assessment algorithm, was incorrectly listed as fusion-bonded epoxy rather than as spiral wrap tape. The coating type data for the accident pipeline segment remained incorrect despite at least one instance of information gathering that documented the error. Different pipeline coating types offer different levels of protection from SCC. Spiral wrap tape coating is known by the pipeline industry to be more vulnerable than other coating types to SCC. Had the coating data in PODS been correctly listed as spiral wrap tape coating, as it was at milepost 496.9, the threat of SCC could likely have been identified. However, Kinder Morgan’s IM program did not identify the threat of SCC at the rupture location and thus did not address it. As a result of this accident, Kinder Morgan corrected their records in PODS. They also tested the section of Line 2000 that ruptured and replaced several areas of pipe. PHMSA issued a corrective action order to Kinder Morgan to shut down the affected pipeline segment, reduce the operating pressure of the pipeline, and develop a plan for reopening the segment. Federal regulations require operators to mathematically calculate a pipeline’s PIR, the area where a pipeline’s potential failure could have a significant impact on people or property. The NTSB calculated the PIR for the rupture site to be 636 feet; however, physical evidence identified during the NTSB’s onsite examination showed that damage to the surrounding vegetation was found up to 878 feet from the rupture crater. Such discrepancies between the calculated PIR and evidence collected at accident scenes has been seen before and prompted the NTSB to further evaluate the assumptions on which the PIR equation is based during the investigation of a pipeline rupture in Danville, Kentucky. On August 15, 2022, NTSB Recommendation P-22-1 was issued to PHMSA: “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.” Footnote: See Pipeline Investigation Report NTSB/PIR-22/02, Enbridge Inc. Natural Gas Transmission Pipeline Rupture and Fire, Danville, Kentucky, August 1, 2019. The recommendation is classified “Open—Acceptable Response.”

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 the 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. 2.3 Calculation of the Potential Impact Radius Federal regulations require operators to mathematically calculate a pipeline’s PIR (the area where a pipeline’s potential failure could have a significant impact on people or property) when deciding whether the pipeline is located in an HCA. The size of the PIR and the accuracy of its calculation directly impact the number and size of HCAs. Gas transmission pipelines that are in HCAs are subject to additional regulatory requirements, such as integrity management regulations. Although Enbridge did perform some integrity management actions on L15 VS4, the NTSB found deficiencies in its IM program, as discussed in sections 2.4, 2.5 and 2.6. The PIR at the rupture site calculated under PHMSA regulations was 633 feet. Physical evidence at the accident site and from the Lincoln County Coroner’s report showed that the PIR of the accident site was larger than what was calculated. The deceased individual was found 640 feet south of the pipeline failure and natural gas fire, and damage to homes was found up to 1,100 feet from the rupture crater. Past accidents have also demonstrated the insufficiency of the PIR calculation. In 2000, a pipeline rupture in Carlsbad, New Mexico, killed 12 people camped about 675 feet from the rupture crater; the PIR would have been calculated at 598 feet by current federal regulations (NTSB 2003). A pipeline that ruptured in San Bruno, California, in 2010 had a PIR of 414 feet, but homes were damaged up to 600 feet from the rupture origin (NTSB 2011). A rupture in Sissonville, West Virginia, in 2012 displayed evidence of thermal damage up to 610 feet from the rupture origin, but the PIR was calculated as 567 feet (NTSB 2014). These discrepancies prompted the NTSB to further evaluate the assumptions on which the PIR equation is based. The NTSB found that the equation is based on nonconservative assumptions, including the flow equation and flow coefficient, which are based on restricted gas flow after the rupture. However, the gas flow from this accident pipeline, as well as that of the other gas pipeline accidents discussed above, was unrestricted because a section of pipeline had been ejected. Unrestricted gas flow rates are significantly higher than restricted gas flow rates. The current PIR equation also assumes a gas flow release factor more consistent with the middle-to-end of a release event, not the beginning, which is when the most significant injuries typically occur. Natural gas fires are more intense at the beginning due to the larger amount of gas and higher pressure. Further, the equation assumes a gas temperature of 59°F; however, temperatures were considerably higher on the ruptured pipeline segment in Danville. Gas flow rates increase with increased temperatures. Assumptions about the impacted public are also inconsistent with available data. The PIR equation assumes a heat radiation intensity of 5,000 BTU/hr-ft2. When calculating a potential impact radius, the lower the allowable heat radiation intensity, the more conservative the equation. In contrast, API Recommended Practice 521, Pressure-Relieving and Depressurizing Systems, recommends only a 1,500 BTU/hr-ft2 heat intensity in areas where exposures lasting 2–3 minutes may be required by personnel without shielding but with appropriate clothing, and just 500 BTU/hr-ft2 heat intensity in areas where personnel with appropriate clothing may be continuously exposed. API Recommended Practice 521 can be used to calculate permissible levels of heat flux for both acute and chronic exposures based on radiation dose load, temperature limits, exposure time, and pain thresholds, among other factors. Appropriate clothing includes items such as fire-resistant clothing, which members of the public cannot be expected to have when a rupture occurs. Thus, the PIR equation uses an acceptable heat radiation intensity at least 3.3 to 10 times the actual maximum survivable level of heat radiation, depending on the length of time the public is exposed to the heat intensity before they are able to leave the area. This does not account for the lack of protective clothing likely to be readily available to the public, which further distorts the survivable level in the presence of heat radiation. In the Danville accident, the off-duty sheriff’s deputy found the injured couple 480 feet from the rupture crater and reported that the intensity of the heat was more than he could handle. He could not approach the decedent, who was 640 feet from the rupture site, because of the heat’s intensity and the duration of his ongoing exposure. PHMSA’s PIR model assumes a 1 percent chance of mortality for a person with 30 seconds of exposure to find shelter. This mortality rate assumes that an individual would take 5 seconds after a fire to analyze the situation, decide to evacuate, run for 25 seconds at 2.5 meters per second, and then successfully find sufficient shelter from the ongoing natural gas fire. Determining the probability of human error is complicated when faced with a circumst

Addressee Acronym: PHMSA

Addressee Organization Type: G-Federal Government

Communication Date: 2023-01-11

Communication Type: Official Correspondence

Communication Contents: We are pleased that you will strongly consider this recommendation. We appreciate the opportunity to speak at the meeting in Houston and to discuss the six pipeline accidents that we investigated (four of which occurred after 2000) before the Danville, Kentucky, accident in which damage or injuries occurred outside of the PIR. We acknowledge that industry may have concerns regarding this recommendation, but we believe the information we presented at the meeting and in our report makes a compelling case for the action we requested. Additionally, we note that you have established a team to review the current PIR calculation methodology. Pending the revision of the PIR calculation methodology based on the available accident and human response data, Safety Recommendation P-22-1 is classified OPEN-- ACCEPTABLE RESPONSE.

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: Strongly Consider. PHMSA established a team to review the current potential impact radius (PIR) calculation methodology, the available accident data, and the human response data to determine if revisions to the pipeline safety regulations are required. Additionally, PHMSA will hold a public meeting in Houston, Texas during the week of December 11, 2022, at which time PHMSA intends to discuss the NTSB Recommendation P-22-1 and receive input from stakeholders on revising the PIR calculation methodology in the regulations. 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.