On January 22, 2026, the Pipeline and Hazardous Materials Safety Administration (PHMSA) published an Advisory Bulletin (ADB-2026-01) to remind owners and operators of natural gas distribution systems of requirements under the distribution integrity management program (DIMP) regulations regarding certain plastic piping and components.

The ADB-2026-01, like all guidance issued by PHMSA, is intended to provide clarity on existing regulatory requirements and an operator’s existing legal obligations. Advisory bulletins are not binding, do not create legally enforceable rights or impose new obligations not contained in the regulations. Nevertheless, the ADB provides important insight into the agency’s regulatory and enforcement priorities.

Incident and NTSB Direction to PHMSA

ADB-2026-01 was issued in response to recommendations made by the National Transportation Safety Board (NTSB) that were developed as a result of its investigation into a natural gas explosion in West Reading, PA on March 24, 2023. The explosion resulted in seven fatalities, 10 injuries, the destruction of one building, and damage to two nearby buildings.

According to the NTSB’s investigation, the probable cause of the incident was degradation of a plastic pipe component, specifically a retired 1982 Aldyl A polyethylene service tee with a Delrin polyacetal insert, due to elevated ground temperature from a corroded underground steam pipe located near the service tee. The degradation allowed natural gas to leak and migrate underground where it was ignited by an unknown source beneath the R.M. Candy Factory Buildings.

NTSB issued Safety Recommendation P-25-2 advising PHMSA to issue an ADB reviewing the details of the incident and advise “all regulated natural gas distribution pipeline operators to address the risk associated with Aldyl A service tees with Delrin inserts, including replacing or remediating them.”

Regulatory Background

Subpart P of 49 CFR part 192 (§§ 192.1001 through 192.1015) of PHMSA’s regulations requires operators of natural gas distribution pipelines to develop and implement a written distribution integrity management program (DIMP) that, among other things, accounts for threats and risks to distribution pipelines. In addition, § 192.325 of PHMSA's regulations require operators of plastic mains to provide “sufficient clearance or insulation from any source of heat so as to prevent the heat from impairing the serviceability of the pipe” when installing new or replaced plastic main(s).

NTSB Investigation

NTSB’s investigation found that the operator was not aware of the steam pipe located in the vicinity of its service tee and thus did not consider the potential impacts of the steam pipe on its pipeline components in its DIMP plan. Specifically, NTSB stated that “without sufficient threat information available for analysis in its [DIMP], [the operator] could not effectively evaluate and address the risk to pipeline integrity of plastic piping in elevated temperature environments and that by not addressing the threat posed by the steam pipe, [the operators] DIMP was not effective in preventing the accident.”[1]

NTSB’s report further noted that crack growth in susceptible plastic piping materials may be increased by elevated ground temperature, and that even small increases in temperature can result in exponential crack growth and thermal decomposition in certain plastic pipeline materials (Delrin insert material in this instance).[2]

In addition, NTSB found that the operator failed to develop and implement procedures for its employees to report elevated sources of ground temperature near its assets, resulting in an inability to identify the potential threat and develop mitigative measures thereto.[3]

Reminders and Recommendations

PHMSA has previously provided operators of distribution pipelines with guidance in identifying threats, ranking risk, and determining and implementing measures designed to reduce the risk of failure. In ADB 2020-02, PHMSA advised that “[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.”

Significantly, PHMSA has addressed the potential threat posed by Aldyl A piping through its Distribution Integrity Management Frequently Asked Questions (FAQs) stating that brittle-like cracking of Aldyl A piping should be considered a threat in a DIMP under the category of “material,” even if operators have not experienced any issues or leaks from Aldyl A piping.

Specifically, ABD-2026-01 offers the following reminders and recommendations to operators of natural gas distribution pipelines that contain plastic pipelines or components.

• Identify the pipeline design and operational characteristics and environmental factors (including sources of elevated temperatures) necessary to assess applicable threats and risks to the distribution pipelines and include those in the operators’ DIMP plan.
• Account for potential environmental threats, such as elevated temperature, operators may be required to complete an inventory of all plastic pipe and components potentially susceptible to premature failure due to slow crack growth or brittle-like cracking or accelerated degradation due to environmental factors. PHMSA also reminds operators that they “must consider, as categories of threat, materials, welds, and any other issues that could threaten the integrity of its pipeline (§ 192.1007(b)). Susceptible materials of plastic assets may include:
  • Plastic pipe installed between 1960 and early 1980s.
  • Low-ductile inner wall Aldyl A piping manufactured by DuPont Company before 1973.
  • Polyethylene gas pipe designated PE 3306.
  • Aldyl A tees with Delrin polyacetal insert.
  • Plexco service tee Celcon (Polyacetal) caps.
  • Driscopipe 7000 and 8000 High Density Polyethylene Pipe.
• Evaluate and rank the risks associated with identified plastic assets that are exposed to, or may be exposed to, elevated temperatures. Importantly, PHMSA reminds operators of prior guidance that higher impact risks, even if less likely to occur than other risks where the impact is not as significant, may require a higher risk ranking in an operator’s DIMP plan.[4]
• Evaluate and include, as appropriate, the following mitigative measures for failures in plastic pipe: effective leak management program (required); pipe replacement or remediation efforts designed to reduce the risk to plastic assets; opportunistic material type verification during routine operation and maintenance; additional leak surveys; or integration of leak survey results to support prioritizing segments for replacement.

For More Information

Van Ness Feldman counsels clients on pipeline safety compliance, enforcement, litigation under state and federal Pipeline Safety Laws and regulations, and with safety requirements applicable to the transportation of hazardous materials. If you would like additional information about PHMSA’s Advisory Bulletin or have questions about any pipeline safety or hazmat matter, please contact Joseph Hainline, Susan Olenchuk, or any member of the firm’s Pipeline & LNG practice group.

[1] NTSB/PIR-25/01 at vii.

[2] NTSB/PIR-25/01 at 58, 67.

[3] NTSB/PIR-25/01 at vii.

[4] ADB-2020-02.