# NTSB Safety Recommendation P-25-011

- **operation:** document
- **citation:** P-25-011
- **title:** NTSB Safety Recommendation P-25-011
- **source type:** guidance
- **agency:** National Transportation Safety Board
- **status:** guidance
- **official:** true
- **published on:** 2025-04-08
- **effective on:** 2025-04-08
- **summary:** TO THE GAS PIPING TECHNOLOGY COMMITTEE: Develop guidance for natural gas pipeline operators to ensure that their distribution integrity management programs appropriately assess and address threats to plastic pipelines posed by nearby assets that may elevate the temperature of the environment near the pipeline.
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- **source url:** https://data.ntsb.gov/carol-main-public/sr-details/P-25-011
**body:**

NTSB safety recommendation P-25-011.

TO THE GAS PIPING TECHNOLOGY COMMITTEE: Develop guidance for natural gas pipeline operators to ensure that their distribution integrity management programs appropriately assess and address threats to plastic pipelines posed by nearby assets that may elevate the temperature of the environment near the pipeline.

Priority: CLASS II

Overall Status: Open - Await Response

Issued Date: 2025-04-08

Adopted Date: 2025-03-18

Synopsis: This report discusses the March 24, 2023, natural gas–fueled explosion and fire at Building 2 of the R.M. Palmer Company, a candy manufacturer located in West Reading, Pennsylvania. The explosion destroyed the manufacturer’s Building 2 and caused significant structural damage to its adjacent Building 1 and other surrounding structures. In total, 7 people were killed, 10 people were injured, and 3 families were displaced from a neighboring apartment building. Safety issues identified in this report include degradation of a retired service tee, insufficient consideration of threats to pipeline integrity, the risk associated with unmarked private pipeline assets crossing public rights-of-way (for example, a public street), delayed evacuation of Building 2 despite detection of natural gas, natural gas safety messaging that may not reach certain members of the public, insufficient guidance on gas leak emergency procedures, absence of natural gas detection alarms in commercial buildings, and insufficient accessibility of gas distribution line valves. As part of this investigation, the National Transportation Safety Board issued recommendations to the Pipeline and Hazardous Materials Safety Administration, the Occupational Safety and Health Administration, 50 states along with the Commonwealth of Puerto Rico and the District of Columbia, the Commonwealth of Pennsylvania, the Pennsylvania Public Utility Commission, the American Gas Association, the American Petroleum Institute, the Gas Piping Technology Committee, the Common Ground Alliance, the International Code Council, the National Fire Protection Association, UGI Corporation, and R.M. Palmer Company.

Probable Cause: The National Transportation Safety Board determines that the probable cause of the explosion was degradation of a retired 1982 Aldyl A polyethylene service tee with a Delrin polyacetal insert that allowed natural gas to leak and migrate underground into the R.M. Palmer Company candy factory buildings, where it was ignited by an unknown source. Contributing to the degradation of the service tee and insert were significantly elevated ground temperatures from steam escaping R.M. Palmer Company’s corroded underground steam pipe, located near the service tee, that had been unmarked and cracked. Contributing to the steam pipe crack was soil movement and R.M. Palmer Company’s lack of awareness of the pipe’s corroded state. Contributing to the natural gas leak was UGI Corporation’s lack of awareness of the nearby steam pipe, which led to an incomplete integrity management program evaluation that did not consider or manage the risk posed by the steam pipe. Contributing to the accident’s severity was R.M. Palmer Company’s insufficient emergency response procedures and training of its employees, who did not understand the hazard and did not evacuate the buildings before the explosion.

Ntsbnumber: PLD23LR002

Report Number: PIR-25-01

Addressee Name: American Gas Association, Gas Piping Technology Committee

Addressee Status: Open - Await Response

Addressee Acronym: GPTC

Addressee Organization Type: A-Associations

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the Gas Piping Technology Committee to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. 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: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the Gas Piping Technology Committee (additional information regarding this recommendation can be found in the noted section of the report): • Develop guidance for natural gas pipeline operators to ensure that their distribution integrity management programs appropriately assess and address threats to plastic pipelines posed by nearby assets that may elevate the temperature of the environment near the pipeline. (P-25-11) (See section 2.3.) The NTSB is vitally interested in this recommendation because it is 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 this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-11). 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. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your organization uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. 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. The NTSB is vitally interested in this recommendation because it is 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 this recommendation. When replying, please refer to the safety recommendation by number (for example, P-25-11). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, 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 report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.3 Insufficient Consideration of Known Threats from Plastic Piping The vulnerability to slow crack growth, also called brittle-like cracking, of early vintage Aldyl A and other early vintage polyethylene piping materials under certain environmental (such as high ground temperatures), installation, and service conditions has been extensively documented. In 1998, the NTSB issued a special investigation report, Brittle-Like Cracking in Plastic Pipe for Gas Service, which concluded that the procedure used in the United States to rate the strength of plastic pipe may have overrated the strength and resistance to brittle-like cracking of much of the plastic pipe manufactured and used for gas service from the 1960s through the early 1980s. The report found that much of this early vintage plastic piping may therefore be susceptible to premature brittle-like cracking failures when subjected to stress intensification (NTSB 1998). In response, PHMSA and its predecessor, the Research and Special Programs Administration, issued four advisory bulletins addressing brittle-like cracking in plastic pipe materials. The 2002 bulletin Notification of the Susceptibility to Premature Brittle-Like Cracking of Older Plastic Pipe warned that “brittle-like cracking (also known as slow crack growth) can substantially reduce the service life of polyethylene piping systems” (Research and Special Programs Administration 2002). The bulletin specifically cited certain Aldyl A piping material manufactured by DuPont Company before 1973—the same material as the retired Building 2 service tee—as potentially susceptible to brittle-like cracking. A 2007 update to the advisory bulletin added Delrin-insert tapping tees to the list of polyethylene pipe materials susceptible to brittle-like cracking. District heating systems that use underground steam pipes like the one used by Palmer can be found throughout the United States, particularly in large cities like New York; San Francisco, California; Philadelphia, Pennsylvania; and Denver, Colorado. Of the 68 district heating systems still operating, just over half were built before 1950—with one quarter built before 1900 (Pierce 2022). The extent of district heating systems nationwide means that other natural gas pipeline operators may have assets near steam pipes. Research has established that elevated temperatures can affect the pressure rating of polyethylene plastic piping, with one study citing the adverse effects of district heating systems on polyethylene gas pipelines (Akhmerova and others 2021). Early vintage Aldyl A piping is
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