Pipeline Safety: Overpressure Protection on Low-Pressure Natural Gas Distribution Systems, 61097-61101 [2020-21508]

Agencies

• Pipeline and Hazardous Materials Safety Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 85, Number 189 (Tuesday, September 29, 2020)]
[Notices]
[Pages 61097-61101]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2020-21508]


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DEPARTMENT OF TRANSPORTATION

Pipeline and Hazardous Materials Safety Administration

[Docket No. PHMSA-2020-0025]


Pipeline Safety: Overpressure Protection on Low-Pressure Natural 
Gas Distribution Systems

AGENCY: Pipeline and Hazardous Materials Safety Administration (PHMSA), 
DOT.

ACTION: Notice; Issuance of advisory bulletin.

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SUMMARY: The Pipeline and Hazardous Materials Safety Administration 
(PHMSA) is issuing this advisory bulletin to remind owners and 
operators of natural gas distribution pipelines of the possibility of 
failure due to an overpressurization on low-pressure distribution 
systems. PHMSA is also reminding such owners and operators of existing 
federal integrity management regulations for gas distribution systems.

ADDRESSES: PHMSA guidance, including the advisory bulletin, can be 
found on PHMSA's website at https://www.phmsa.dot.gov/guidance.

FOR FURTHER INFORMATION CONTACT: 
    Technical Questions: Michael Thompson, Transportation Specialist, 
by phone at 503-883-3495 or by email at [email protected].
    General Questions: Ashlin Bollacker, Technical Writer, by phone at 
202-366-4203 or by email at [email protected].

SUPPLEMENTARY INFORMATION:

I. Natural Gas Distribution Systems

    Natural gas distribution systems deliver natural gas to customers 
for heating, cooking, and other domestic and industrial uses. A basic 
natural gas distribution system has four elements: (1) Mains that 
transport gas underground; (2) service lines that deliver natural gas 
from the main to the customer; (3) regulators that control the pressure 
of gas to a designated value; and (4) meters that measure the quantity 
of natural gas used by each customer. Customer piping takes natural gas 
from the meter to the customer's heating equipment and other 
appliances.
    There are two types of natural gas distribution systems used to 
supply natural gas to the customer: High-pressure distribution systems 
and low-pressure distribution systems. In a high-pressure distribution 
system, the gas pressure in the main is higher than the pressure 
provided to the customer. A pressure regulator installed at each meter 
reduces the pressure from the main to a pressure that can be used by 
the customer's equipment and appliances. These regulators incorporate 
an overpressure protection device to prevent overpressurization of the 
customer's piping and appliances should the regulator fail. 
Additionally, as of April 14, 2017, all new or replaced service lines 
connected to a high-pressure distribution system must have excess flow 
valves. (Sec.  192.383).\1\ Excess flow valves can reduce the risk of 
overpressurization in natural gas distribution pipelines by shutting 
off unplanned, excessive gas flows. Because each customer's service 
line in a high-pressure distribution system is protected by an excess 
flow valve and a pressure regulator, it is highly unlikely that an 
overpressurization condition in the main would impact customers.
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    \1\ PHMSA published the final rule, ``Pipeline Safety: Expanding 
the Use of Excess Flow Valves in Gas Distribution Systems to 
Applications Other Than Single-Family Residences,'' on October 14, 
2016, but delayed the effective date by six months to give operators 
time to comply with the new provisions. (81 FR 70987). A copy of 
this final rule is available in the docket PHMSA-2011-0009 at 
https://www.regulations.gov.
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    In a low-pressure natural gas distribution system, however, the 
natural gas in a distribution pipeline flows predominantly at the same 
pressure as the pressure contained within the customer's service line 
piping. Natural gas is typically supplied to distribution pipeline 
mains from a high-pressure source that connects to, and flows through, 
a regulator station. The regulator station functions to reduce the 
pressure to a level that allows the gas to flow continuously at a low 
pressure all the way to premises of the customers where the gas is 
ultimately consumed. Since there are no regulators at the customer 
meter set in a low-pressure system, an overpressure condition occurring 
on the distribution system can affect all customers served by the 
system in the event that the regulator(s) that controls the pressure 
for the system fails. This scenario is what happened in the September 
13, 2018, accident in Merrimack Valley that prompted the subsequent 
National Transportation Safety Board (NTSB) report and recommendations.

II. CMA's Accident in Merrimack Valley

A. Accident Synopsis

    On September 13, 2018, a series of structure fires and explosions 
occurred after high-pressure natural gas entered a low-pressure natural 
gas distribution system operated by Columbia Gas of Massachusetts 
(CMA), a subsidiary of NiSource, Inc.\2\ CMA delivers natural gas to 
about 325,000 customers in Massachusetts. According to an investigation 
of the accident conducted by the National Transportation Safety 
Board,\3\ the fires and explosions damaged 131 structures, including at 
least 5 homes that were destroyed in the city of Lawrence and the towns 
of Andover and North Andover. CMA shut down the low-pressure natural 
gas distribution system serving 10,894 customers, including some 
outside the affected area who had their service shut off as a 
precaution. An 18-year-old male was killed when a home exploded, and 
the house's chimney fell onto the vehicle where he was sitting. Another 
person in the vehicle at the time of the explosion was seriously 
injured, as was someone on the second floor of the house. In total, 22 
people, including 3 firefighters, were transported to hospitals for 
treatment of their injuries.
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    \2\ CMA is expected to be officially transferred by NiSource, 
Inc., to Eversource Energy in November 2020.
    \3\ ``Pipeline Accident Report: Overpressurization of Natural 
Gas Distribution System, Explosions, and Fires in Merrimack Valley, 
Massachusetts; September 13, 2018.'' The National Transportation 
Safety Board. Accident Report: NTSB/PAR-19/02. Adopted September 24, 
2019.
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B. Background on CMA's Natural Gas Main Replacement Project

    The low-pressure natural gas distribution system in the Merrimack 
Valley was installed in the early 1900s and was constructed with cast 
iron mains. The system was designed with 14 regulator stations to 
control the pressure of natural gas entering the downstream 
distribution pipeline mains. Each regulator station contained two 
regulators in series--a ``worker regulator'' and a ``monitor 
regulator''--each with a sensing line connected to a downstream section 
of main for the purpose of providing a pressure measurement back to the 
regulator station so that the system could be maintained at a specified 
pressure level of 0.5 pounds per square inch. The

[[Page 61098]]

``worker'' regulator is the primary regulator that maintains the 
natural gas pressure, and the ``monitor'' regulator provides a 
redundant backup to the ``worker'' regulator. Each of the regulator 
stations reduced the natural gas pressure from about 75 pounds per 
square inch gauge (psig) to 12 inches of water column (w.c.), or about 
0.5 psig, for distribution through the mains and delivery to 
customers.\4\
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    \4\ In the pipeline industry, it is customary to measure 
anything less than 1 psig in inches of water column. A measurement 
of 1 inch w.c. equals 0.0361 psig.
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    Beginning in 2016, CMA initiated an effort to replace 7,595 feet of 
low-pressure cast iron and bare steel mains with 4,845 feet of low-
pressure and high-pressure polyethylene (plastic) mains. CMA contracted 
with Feeney Brothers, a pipeline services firm, to complete the 
replacement project. A work package, which included materials such as 
isometric drawings and procedural details for disconnecting and 
connecting pipes, was prepared for each of the planned construction 
activities. However, no package was prepared for the relocation of the 
Winthrop Avenue sensing lines serving the Winthrop Avenue regulator 
station.
    The first stage of the project involved the installation of the 
plastic main, which was completed in late 2016. The regulator sensing 
lines at the Winthrop Avenue regulator station remained attached to the 
cast iron main that would ultimately be decommissioned.
    CMA connected the plastic pipe to the distribution system, which 
allowed it to be monitored for pressure changes. The second stage of 
the project began in 2018 and involved the installation of tie-ins to 
the new plastic main, after which the legacy cast iron mains would be 
decommissioned and abandoned in their existing location. On the day of 
the accident, the sensing lines were still connected to the abandoned 
cast iron main.
    At the Winthrop Avenue regulator station, about 0.5 mile south of 
the work area, the sensing lines connected to the abandoned cast iron 
mains continued providing data input to the two pressure regulators 
used to control the system pressure.\5\ Once the contractor crew 
isolated the cast iron main, the natural gas pressure began to drop in 
the cast iron main and the sensing lines continued to provide those 
readings to the regulator station. As the pressure dropped, the 
pressure regulators responded by opening further to inject more gas to 
into the downstream system to the newly installed plastic system. 
Because there were no sensing lines connecting the regulator station to 
the newly installed plastic mains, the legacy sensing lines continued 
to provide ``zero'' pressure readings to Winthrop Avenue regulators, 
thereby causing them to fully open and provide a continuous flow of gas 
into the new low-pressure plastic system, resulting in an extreme 
overpressurization of the distribution system. This immediately 
resulted in multiple fires, explosions, and injuries.
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    \5\ Sensing lines are also called control lines or static lines.
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C. National Transportation Safety Board (NTSB) Accident Investigation 
and Recommendations

    Since the accident, the National Transportation Safety Board (NTSB) 
issued several safety recommendations. On November 14, 2018, NTSB 
recommended that the operator, NiSource Inc.:
     Revise the engineering plan and constructability review 
process across all of its subsidiaries to ensure that all applicable 
departments review construction documents for accuracy, completeness, 
and correctness, and that the documents or plans be sealed by a 
professional engineer prior to commencing work (P-18-6);
     Review and ensure that all records and documentation of 
its natural gas systems are traceable, reliable, and complete (P-18-7);
     Apply management of change process to all changes to 
adequately identify system threats that could result in a common mode 
failure (P-18-8); and
     Develop and implement control procedures during 
modifications to gas mains to mitigate the risks identified during 
management of change operations. Gas main pressures should be 
continually monitored during these modifications and assets should be 
placed at critical locations to immediately shut down the system if 
abnormal operations are detected (P-18-9).
    In response, NiSource Inc. has taken actions that satisfied the 
NTSB's recommendations, which are now classified as ``Closed.''
    On September 24, 2019, the National Transportation Safety Board 
(NTSB) issued its accident report and identified the probable cause of, 
and contributing factors to, CMA's accident in Merrimack Valley. NTSB 
found that the probable cause of the accident was CMA's weak 
engineering management that failed to adequately plan, review, 
sequence, and oversee the construction project that abandoned the cast 
iron main without first relocating the regulator sensing lines to the 
new plastic main. NTSB also found that a contributing cause of the 
accident was a low-pressure natural gas distribution system that was 
designed and operated without adequate overpressure protection. As a 
result of its investigation, NTSB made several recommendations to 
NiSource, Inc., the Commonwealth of Massachusetts and several other 
States, and PHMSA. NTSB made two recommendations to PHMSA. The first 
(P-19-14) called for PHMSA to ``revise Title 49 Code of Federal 
Regulations Part 192 to require overpressure protection for low-
pressure natural gas distribution systems that cannot be defeated by a 
single operator error or equipment failure.'' Having investigated 
multiple overpressurization accidents over the past 50 years, NTSB 
concluded that low-pressure natural gas distribution systems that use 
only sensing lines and regulators to detect and prevent 
overpressurization are not optimal to prevent overpressurization 
accidents.
    NTSB's second recommendation (P-19-15) called for PHMSA to ``issue 
an alert to all low-pressure natural gas distribution system operators 
of the possibility of a failure of overpressure protection, and the 
alert should recommend that operators use a failure modes and effects 
analysis (FMEA) or equivalent structured and systematic method to 
identify potential failures and take action to mitigate those 
identified failures.'' NTSB found that CMA's constructability review 
\6\ process was not sufficiently robust to detect the omission of a 
work order to relocate the sensing lines; and that CMA's engineering 
risk management processes were deficient. NTSB explained that for 
regulator sensing lines, CMA only considered excavation damage as a 
risk to be mitigated. NTSB concluded that a comprehensive and formal 
risk assessment, such as FMEA, would have identified the human error 
that caused the redundant regulators to open and over pressurize the 
low-pressure system.
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    \6\ ``Constructability reviews'' are a recognized and generally 
accepted good engineering practice commonly used for the execution 
of professional design services and are intended to provide an 
independent and structured review of construction plans and 
specifications to ensure there are no conflicts, errors, or 
omissions.
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    In response to NTSB's recommendation P-19-15, PHMSA is issuing this 
advisory bulletin to remind owners and operators of low-pressure 
natural gas distribution systems of the possibility of a failure of 
overpressure protection devices. Currently, there are Federal 
regulations in place that specify several minimum safety standards 
requiring operators to account for the possibility of overpressure 
events in the

[[Page 61099]]

design and operation of their systems. Specifically, the Distribution 
Integrity Management Program (DIMP) regulations at 49 CFR 192.1005 
require operators of natural gas distribution systems to develop and 
implement an integrity management program for pipelines they own, 
operate, or maintain. Under DIMP, operators must identify existing and 
potential threats to the integrity of their systems, and to rank the 
risks so that known issues can be evaluated by the risks they pose. 
PHMSA agrees with the NTSB that low-pressure distribution system 
operators need to be reminded of their obligation to identify all 
threats to their systems and take mitigative measures in accordance 
with the risks to their systems. The diversity of designs and operating 
conditions of those systems mean that the risks associated with 
overpressure conditions may be best managed by a combination of design 
elements and engineering practices tailored to the unique attributes 
and conditions of their specific systems that pipeline operators are 
best positioned to identify and implement. Therefore, PHMSA is 
reminding operators of low-pressure distribution systems of their 
existing obligations under the DIMP regulations to consider and 
implement such tailored approaches to mitigate or eliminate the risk of 
an overpressurization event.

D. Distribution Integrity Management Program Regulatory Provisions

    PHMSA first adopted integrity management regulations for hazardous 
liquid pipelines in 2000, then for gas transmission pipelines in 2003. 
Subsequently, the Pipeline Integrity, Protection, Enforcement, and 
Safety Act of 2006 (PIPES Act of 2006; Pub. L. 109-468) mandated that 
PHMSA prescribe minimum safety standards to extend integrity management 
to gas distribution pipeline systems. The 2006 legislation directed 
PHMSA to require operators of distribution pipelines to identify and 
assess risks on their distribution lines, to remediate conditions that 
present a potential threat to pipeline integrity, and to monitor 
program effectiveness. In response to that mandate, PHMSA implemented 
new requirements in 49 CFR part 192, subpart P, that rely on operator-
specific programs to improve the overall integrity of pipeline systems 
and reduce risk (74 FR 63905; December 4, 2009). PHMSA concluded that 
this performance-based approach was a more effective method for 
improving pipeline system safety--given the diversity of distribution 
systems and the particular threats to which different systems may each 
be exposed--than imposing a ``one-size-fits-all'' prescriptive 
requirement.
    The DIMP regulations require operators of natural gas distribution 
systems to develop, write, and implement an integrity management 
program for pipelines they own, operate, or maintain. An integrity 
management plan is a written set of policies and procedures that each 
operator must develop and implement to ensure compliance. Pursuant to 
Sec.  192.1007,\7\ an integrity management plan must include procedures 
for implementing the following elements:
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    \7\ ``Pipeline Safety: Integrity Management Program for Gas 
Distribution Pipelines.'' Final Rule. (74 FR 63905; Dec. 4, 2009). 
https://www.federalregister.gov/documents/2009/12/04/E9-28467/pipeline-safety-integrity-management-program-for-gas-distribution-pipelines#h-22
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     Periodically assess and improve the integrity management 
program; and
     Report performance results to PHMSA and, where applicable, 
also to state public utility commissions.
    a. Knowledge (192.1007(a)). This section requires an operator to 
develop an understanding of its distribution pipeline. An operator must 
identify the characteristics of its pipeline's design and operations, 
and of the environment in which it operates, which are necessary to 
assess applicable threats and risks. This must include considering 
information gained from past design, operations, and maintenance. This 
section further requires that operators develop their understanding 
from reasonably available information. Operators have considerable 
knowledge of their pipeline to support routine operations and 
maintenance, but this information may be distributed throughout the 
company, in possession of groups responsible for individual functions. 
Operators must assemble this information to the extent necessary to 
support the development and implementation of their IM program.
    PHMSA recognizes that there may be gaps in the knowledge an 
operator possesses when it develops its initial IM plan. Operators must 
identify these gaps and the additional information needed to improve 
their understanding. Operators are required to provide a plan for 
gaining that information over time through the normal activities of 
operating and maintaining pipeline systems (e.g., collecting 
information about underlying components when portions of the pipeline 
must be excavated for other reasons). Operators must also develop a 
process by which the program will be periodically reviewed and refined, 
as needed.
    b. Identify threats ((Sec.  192.1007(b)). Identification of the 
threats that affect, or could potentially affect, a distribution 
pipeline remains critical to ensuring integrity. Knowledge of 
applicable threats allows operators to evaluate the safety risks they 
pose and to rank those risks, allowing safety resources to be applied 
where they will be most effective. This section requires that operators 
consider the general categories of threats that must be reported on 
annual reports. Operators are required to consider reasonably available 
information to identify threats that affect their pipeline or that 
could potentially affect it (e.g., landslides in a hilly area with 
loose soils even if no landslide has been experienced). The section 
specifies that operators should minimally consider data sources 
resulting from normal operation and maintenance in evaluating threats.
    c. Evaluate and rank risk (192.1007(c)). This section requires that 
an operator evaluate the identified threats to determine their relative 
importance and rank the risks associated with its pipeline. Operators 
must consider the likelihood of threats and the consequences of a 
failure that might result from each threat. Consideration of 
consequences is important to help ensure that risks are properly 
ranked. A potential accident of relatively low probability but that 
would produce significant consequences should be considered to be of 
higher risk than an accident with somewhat greater likelihood, but one 
that is not expected to produce major consequences.
    d. Identify and implement measures to address risks (Sec.  
192.1007(d)). This section requires operators to determine and 
implement measures designed to reduce the risk of failure of gas 
distribution pipeline systems.
    e. Measure performance, monitor results, and evaluate effectiveness 
(Sec.  192.1007(e)). This section requires operators to develop 
performance measures, including some that are specified for use by all 
operators. Measuring performance periodically enables operators to 
determine whether actions being taken to address threats are effective, 
or whether different or additional actions are needed. An operator must 
also periodically re-evaluate the threats and risks to its gas 
distribution pipeline.
    f. Periodic evaluation and improvement (Sec.  192.1007(f)). This 
section requires operators to re-evaluate risks across the entire 
pipeline system periodically and to consider the relevance of threats 
in one specific location as compared to other locations.

[[Page 61100]]

Operators must consider the results of their performance monitoring in 
these evaluations, which must be performed at least once every five 
years. An operator must determine an appropriate period for conducting 
a complete program evaluation based on the complexity of its system. An 
operator should conduct a program evaluation any time there are changes 
in factors that would increase the risk associated with a failure.
    While DIMP regulations have been in place since 2009, some 
operators may not be sufficiently aware of their pipeline attributes, 
nor adequately or consistently assessing threats as part of their DIMP 
programs. Early in the investigation, NTSB determined that several of 
NiSource's engineering processes were deficient. For example, the NTSB 
found that CMA's inadequate planning, documentation, and recordkeeping 
processes led to the omission of the relocation of sensing lines during 
a construction project. Further, NTSB found that CMA's constructability 
review process was not sufficiently robust to detect the omission of a 
work order to relocate sensing lines. It was the abandonment of the 
cast iron main without first relocating the sensing lines that led 
directly to the accident. Thus, it is necessary to identify and 
evaluate the physical and operational characteristics of each pipeline 
system to evaluate risks adequately. It is also important that an 
operator focus its DIMP on identifying the conditions that can cause 
failures and address them before a failure occurs. Therefore, PHMSA is 
reminding owners and operators of their continuing obligation to comply 
with DIMP regulations and is alerting operators that PHMSA considers 
the possibility of an overpressure protection failure to be a high-risk 
threat. PHMSA reminds operators of low-pressure systems that they must 
consider reasonably available information about possible threats to 
their gas distribution system, including such sources as the NTSB 
report, industry publications, and this advisory bulletin.
    As part of the DIMP plans, PHMSA recommends that operators enhance 
their processes and procedures by including a failure modes and effects 
analysis, or equivalent structured and systematic method of risk 
analysis. Including a failure mode and effect analysis or equivalent 
methodology can help identify and mitigate the possibility of an 
overpressure failure event. PHMSA also urges operators to develop and 
implement procedures for construction-related work that are specific to 
low-pressure distribution systems, such as repairs, uprates in 
pressure, or replacement of pipeline or pressure regulation facilities.

II. Advisory Bulletin (ADB-2020-02)

    To: Owners and Operators of Natural Gas Distribution Systems
    Subject: Overpressure Protection on Low-pressure Natural Gas 
Distribution Systems.
    Advisory: PHMSA is reminding all owners and operators of low-
pressure natural gas distribution systems of the risk of failure of 
overpressure protection systems. This advisory bulletin is intended to 
clarify for the public existing pipeline safety standards and highlight 
the importance of evaluating and implementing overpressure protection 
design elements and operational practices within their compliance 
programs. The contents of this advisory bulletin do not have the force 
and effect of law. They are not meant to bind the public in any way, 
even as pipeline owners and operators must comply with the underlying 
safety standards.
    PHMSA encourages operators to review the NTSB's Pipeline Accident 
Report concerning Columbia Gas of Massachusetts' (CMA) 
overpressurization event in the Merrimack Valley on September 13, 2018. 
It may be instructive regarding a host of potential safety problems 
that operators of low-pressure natural gas distribution systems may 
need to address. A copy of NTSB's accident report is contained within 
Docket No. PHMSA-2020-0025 for this advisory bulletin.
    PHMSA also reminds pipeline operators of their obligations to 
comply with the gas DIMP regulations at 49 CFR part 192, subpart P. 
Under DIMP, gas distribution operators must have knowledge of their 
pipeline systems; identify threats to their systems; evaluate and rank 
risks; and identify, evaluate, and implement measures to address those 
risks. CMA's accident in Massachusetts highlights the need for 
operators of low-pressure systems to review thoroughly their current 
DIMP for the threat of overpressurization and to make any necessary 
changes or modifications to become fully compliant with the Federal 
Pipeline Safety Regulations (Sec.  192.1007(f)).

Written Procedures (Sec.  192.1005)

    Developing and implementing comprehensive written procedures with 
sufficient specificity is one of the most effective ways to prevent 
overpressurization of a low-pressure gas system. Therefore, PHMSA 
reminds operators of low-pressure systems to review their written 
integrity management plans to help ensure that they comply with Sec.  
192.1005 and to ensure that they specifically address the risk of an 
overpressurization event. PHMSA further recommends, in addition to 
having procedures for operations, maintenance, and emergencies (Sec.  
192.605), that operators develop written procedures for all activities 
involving new construction or pipe replacement projects for low-
pressure distribution systems. PHMSA recommends that these procedures 
account for the additional precautions needed to protect those systems 
from an overpressurization event. These procedures should include:
     Clear roles and responsibilities across all departments 
involved in the planning and execution of construction or pipe 
replacement projects;
     Description and delineated scope of work to be conducted, 
with a materials list, necessary schematics, and maps of the location 
of the work;
     Requirements to review and ensure that all records and 
documentation of the affected gas system(s) are traceable, reliable, 
and complete;
     The sequential process of how the work is to be carried 
out and who or what group is responsible for each step;
     Application of a ``management of change'' process to 
identify all changes that could threaten system integrity, particularly 
where there is a risk emanating from a common mode of failure, 
including a list of individuals and groups necessary for review along 
with their comment and approval before work commences; and
     Implement a review process sufficiently robust to detect 
the omission of critical process and procedural steps that could 
prevent possible overpressurization events.

Knowledge of Distribution System (Sec.  192.1007(a))

    PHMSA reminds operators that they are required to develop 
procedures in their DIMP that demonstrate an understanding of their gas 
distribution systems (Sec.  192.1007(a)). An operator must identify the 
characteristics of its pipeline design and operations, and of the 
environment in which it operates, in the process of assessing 
applicable threats and risks. Section 192.1007(a) requires that 
operators develop their understanding from reasonably available 
information. This must include information gained from past design, 
operations, and maintenance. If an operator acquires a pipeline and the 
historical records were not obtained or are not reasonably available, 
the records do not need to be re-created. However,

[[Page 61101]]

operators must assemble this information to the extent necessary to 
support the development and implementation of their integrity 
management programs. Underlying procedures must also identify 
additional information necessary to improve their understanding and 
provide a plan for gaining that information over time through the 
normal activities of operating and maintaining pipeline systems (e.g., 
collecting information about buried components when portions of the 
pipeline must be excavated for other reasons). Operators must also 
develop a process by which the program will be periodically reviewed 
and refined, as needed. The outcome of the process should be that all 
affected departments of an operator's organization are aware of any 
planned construction work, have had the opportunity to review and 
provide comments on potential failure modes and to adopt a process for 
providing final approval of construction procedures.

Identifying Threats and Ranking Risk (Sec.  192.1007(b)-(c))

    PHMSA reminds operators of their obligation under DIMP regulations 
(part 192, subpart P) to consider available information when 
identifying all potential and existing threats to the integrity of 
their systems (Sec.  192.1007(b)). In accordance with Sec.  
192.1007(b), operators are required to consider seven specific threats, 
including equipment failure and incorrect operation. Further, PHMSA 
reminds operators to evaluate the risks associated with their 
distribution pipelines, determine the relative importance of each 
threat, and rank the risks posed to their pipeline systems (Sec.  
192.1007(c)). PHMSA reminds operators that consideration of 
consequences is important to help ensure that risks are properly 
ranked. A potential accident of relatively low likelihood but one that 
would produce significant consequences may be a higher risk than an 
accident with somewhat greater likelihood, but one that is not expected 
to produce major consequences.
    Given the catastrophic consequences of the Merrimack Valley 
accident, PHMSA considers the possibility of an overpressure protection 
system failure to be a high-risk threat for low-pressure distribution 
systems where there are not adequate provisions to protect such 
systems. Therefore, PHMSA recommends that operators consider the single 
point of failure that could lead to an overpressurization of a low-
pressure system as a high-risk threat and to review and adjust their 
DIMP plans accordingly. NTSB's Pipeline Accident Report sufficiently 
documents the occurrence of overpressurization of low-pressure 
distribution systems such that the threat of overpressurization should 
be considered a real and present threat. If the threat of 
overpressurization of low-pressure distribution systems is not 
considered an existing threat by an operator, justification for the 
elimination of this threat from consideration should be documented.
    In performing a risk analysis required by DIMP (Sec.  192.1007), 
PHMSA recommends operators use a failure modes and effectiveness 
analysis (FMEA) model or an equivalent structured and systematic method 
to identify and mitigate risks. Failure modes and effects analysis 
(FMEA) is a generally accepted and recognized engineering practice used 
to identify and assess potential failures, including common mode 
failures. As NTSB concluded, a comprehensive and formal risk 
assessment, such as FMEA, would have identified the human error that 
caused the redundant regulators to open and over-pressurize the low-
pressure system. Operators may already be leveraging FMEA or other 
similarly robust methodologies to perform the risk analysis and should 
continue to do so. PHMSA recommends that operators consider adopting 
FMEA or another qualitative tool that may help to identify possible 
failures or consequences of those failures that would not be identified 
otherwise.

Identify and Implement Measures To Address Risk (Sec.  192.1007(d))

    PHMSA reminds operators that they must determine and implement 
measures designed to reduce the risk of failure on their pipeline 
systems (Sec.  192.1007(d)). If additional actions have not been taken 
to reduce risks, justification should be documented (e.g., current 
overpressure protection design was determined to be sufficient; risks 
were deemed to be low).
    There are several ways that operators can protect low-pressure 
distribution systems from overpressure events. Some notable examples 
include:
     Installing a full-capacity relief valve downstream of the 
low-pressure regulator station, including in applications where there 
is only worker-monitor pressure control;
     Installing a ``slam shut'' device;
     Using telemetered pressure recordings at district 
regulator stations to signal failures immediately to operators at 
control centers; and
     Completely and accurately documenting the location for all 
control (i.e., sensing) lines on the system.

Measure Performance, Monitor Results, and Evaluate Effectiveness (Sec.  
192.1007(e))

    PHMSA reminds operators that they must monitor performance measures 
from an established baseline to evaluate the effectiveness of DIMP 
(Sec.  192.1007(e)). Section 192.1007(e)(vi) requires that these 
performance measures include any additional measures determined 
necessary to control identified threats. PHMSA reminds operators to 
modify their DIMP as appropriate, considering the potential failure of 
overpressure protection systems as a high-risk threat.

    Issued in Washington, DC, on September 24, 2020, under authority 
delegated in 49 CFR 1.97.
Alan K. Mayberry,
Associate Administrator for Pipeline Safety.
[FR Doc. 2020-21508 Filed 9-28-20; 8:45 am]
BILLING CODE 4910-60-P