# NTSB Safety Recommendation P-91-016 **Citation:** P-91-016 **Type / status:** guidance / guidance **Agency:** National Transportation Safety Board **Effective:** 1991-08-06 **Published:** 1991-08-06 THE NTSB RECOMMENDS THAT THE UGI CORPORATION: DOCUMENT THE LOCATION OF UNDERGROUND VOIDS DISCOVERED DURING EXCAVATIONS AND COORDINATE WITH THE CITY OF ALLENTOWN TO DEVELOP SYSTE MATIC PROCEDURES FOR CENTRALLY REPORTING, DOCUMENTING, EXCHANGING INFORMATION ON THE LOCATION OF UNDERGROUND VOIDS. ## Document text NTSB safety recommendation P-91-016. THE NTSB RECOMMENDS THAT THE UGI CORPORATION: DOCUMENT THE LOCATION OF UNDERGROUND VOIDS DISCOVERED DURING EXCAVATIONS AND COORDINATE WITH THE CITY OF ALLENTOWN TO DEVELOP SYSTE MATIC PROCEDURES FOR CENTRALLY REPORTING, DOCUMENTING, EXCHANGING INFORMATION ON THE LOCATION OF UNDERGROUND VOIDS. Priority: CLASS II Overall Status: Closed - Acceptable Action Issued Date: 1991-08-06 Adopted Date: 1991-07-23 Overall Date Closed: 1993-04-16 Synopsis: ON 8/29/90, A NATURAL GAS EXPLOSION & FIRE DESTROYED TWO ROW HOUSES AT 421-423 NORTH FIFTH STREET & DAMAGED TWO ADJACENT HOUSES & THREE PARKED CARS IN ALLENTOWN, PA. ONE PERSON WAS KILLED, & NINE PEOPLE, INCLUDING TWO FIREFIGHTERS, WERE INJURED. THE NTSB'S INVESTIGATION DISCLOSED THAT WATER LEAKING FROM A CIRCUMFERENTIAL CRACK IN A 6-INCH CAST-IRON MUNICIPAL WATER MAIN BENEATH NORTH FIFTH STREET'S EAST SIDE HAD ERODED THE SOIL FOUNDATION OF A LOW PRESSURE (9 INCHES WATER COLUMN PRESSURE) 4-INCH CAST-IRON UGI CORPORATION (UGI) GAS MAIN BENEATH THE WEST SIDE OF NORTH FIFTH STREET. THE GAS MAIN SUBSEQUENTLY CRACKED CIRCUMFERENTIALLY AND NATURAL GAS FILLED THE VOID BENEATH THE PAVEMENT. NATURAL GAS THEN MIGRATED THROUGH THE SOIL & INTO THE BASEMENT OF 423 NORTH FIFTH STREET, WHERE IT IGNITED, EXPLODED, & BURNED. SUBSEQUENT METALLURGICAL EXAMINATIONS REVEALED THAT BOTH CAST-IRON MAINS WERE SIGNIFICANTLY WEAKENED BY GRAPHITIC CORROSION. THE WATER MAIN WAS INSTALLED IN THE LATE 1800S & THE GAS MAIN WAS INSTALLED IN 1903. Probable Cause: Undermined and weakened segment of cast-iron gas main Ntsbnumber: DCA90FP011 Report Number: PAB-91-01 Addressee Name: UGI Corporation Addressee Status: Closed - Acceptable Action Addressee Date Closed: 1993-04-16 Addressee Organization Type: P-Private Industry Communication Date: 1991-10-17 Communication Type: Official Correspondence Communication Contents: UGI WILL CONTACT THE CITY OF ALLENTOWN WITHIN 30 DAYS OF THE DATE OF THIS RESPONSE TO BEGIN DISCUSSIONS LEADING TO THE DEVELOPMENT OF SYSTEMATIC PROCEDURES FOR CENTRALLY REPORTING, DOCUMENTING, AND EXCHANGING INFORMATION ON THE LOCATION OF UNDERGROUND VOIDS WITHIN THE CITY. IT IS UGI'S INTENT TO USE THE INFORMATION, AND PROCEDURES, GAINED IN THESE DISCUSSIONS TO POTENTIALLY EXPAND THIS TYPE OF SERVICE IN OTHER PORTIONS OF OUR DISTRIBUTION SYSTEM. Addressee Organization Type: P-Private Industry Communication Date: 1992-03-26 Communication Type: Official Correspondence Communication Contents: UGI MET WITH CITY OF ALLENTOWN REPRESENTIATIVES ON 1-29-92. THE MEETING WAS PRODUCTIVE AND BOTH PARTIES AGREED TO APPROACH THE PA. ONE CALL SYSTEM (POCS) AS A POTENTIAL RECIPIENT AND DISSEMINATOR OF INFORMATION REGARDING UNDERGROUND VOIDS WITHIN THE CITY. UGI HAS HAD PRELIMINARY DISCUSSIONS WITH POCS CONCERNING THIS SERVICE. BECAUSE POCS IS RENEGOTIATING ITS OUTSIDE VENDOR CONTRACTS AT THIS TIME, FINAL AGREEMENT WOULD HAVE TO WAIT UNTIL AFTER 5/31/92. UGI AND THE CITY OF ALLENTOWN WILL PURSUE THIS POTENTIAL SOLUTION AT THAT TIME. Addressee Organization Type: P-Private Industry Communication Date: 1993-02-25 Communication Type: Official Correspondence Communication Contents: THE CITY OF ALLENTOWN AND UGI HAVE AGREED TO USE THE PENN. ONE CALL SYSTEM AS THE RECIPIENT AND DISSEMINATOR OF INFORMATION REGARDING SINKHOLES WITHIN THE CITY OF ALLENTOWN. Addressee Organization Type: P-Private Industry Communication Date: 1992-07-08 Communication Type: Official Correspondence Communication Contents: THE SAFETY BOARD UNDERSTANDS THAT UGI HAS MET WITH CITY OF ALLENTOWN AND PENNSYLVANIA ONE CALL SYSTEM REPRESENTATIVES ON SEVERAL OCCASIONS TO DISCUSS THE ISSUE OF UNDERGROUND VOIDS. Addressee Organization Type: P-Private Industry Communication Date: 1993-04-16 Communication Type: Official Correspondence Communication Contents: THE BOARD UNDERSTANDS THAT UGI & THE CITY OF ALLENTOWN HAVE AGREED TO USE THE PENNSYLVANIA ONE CALL SYSTEM AS THE RECIPIENT & DISSEMINATOR OF INFO REGARDING SINKHOLES WITHIN THE CITY OF ALLENTOWN. BASED ON THIS INFO, P-91-16 HAS BEEN CLASSIFIED "CLOSED--ACCEPTABLE ACTION." Addressee Organization Type: P-Private Industry Communication Date: 1992-01-28 Communication Type: Official Correspondence ## Provenance - Official: Yes - Source: - Source ID: `ntsb-pipeline` - SHA-256: `1996f36afac5e96acbac61a86d64e6bb764411e753b106649e1ba9724e147510` - Retrieved: 2026-08-20T04:57:24.741Z - Exported: 2026-08-24T07:29:33.092Z - Document slug: `ntsb-recommendation-p-91-016` ### Source metadata ```json { "recordKind": "ntsb_safety_recommendation", "safetyRecommendationNumber": "P-91-016", "recommendationMode": "Pipeline", "topicMode": "Pipeline", "ntsbNumber": "DCA90FP011", "priority": "CLASS II", "overallStatus": "Closed - Acceptable Action", "overallStatusAcronym": "CAA", "overallDateClosed": "1993-04-16", "lastModifiedDate": "2016-11-15", "reportNumber": "PAB-91-01", "reportUrl": "https://www.ntsb.gov/investigations/Pages/DCA90FP011.aspx", "transmittalLetterUrl": "http://www.ntsb.gov/safety/safety-recs/recletters/P91_13_16.pdf", "addressees": [ { "addresseeName": "UGI Corporation", "addresseeStatusAcronym": "CAA", "addresseeStatus": "Closed - Acceptable Action", "addresseeDateClosed": "1993-04-16", "addresseeDetails": [ { "addresseeAcronym": null, "addresseeOrganizationType": "P-Private Industry", "isFromNtsb": false, "communicationDate": "1991-10-17", "communicationType": "Official Correspondence", "communicationContents": "UGI WILL CONTACT THE CITY OF ALLENTOWN WITHIN 30 DAYS OF THE DATE OF THIS RESPONSE TO BEGIN DISCUSSIONS LEADING TO THE DEVELOPMENT OF SYSTEMATIC PROCEDURES FOR CENTRALLY REPORTING, DOCUMENTING, AND EXCHANGING INFORMATION ON THE LOCATION OF UNDERGROUND VOIDS WITHIN THE CITY. IT IS UGI'S INTENT TO USE THE INFORMATION, AND PROCEDURES, GAINED IN THESE DISCUSSIONS TO POTENTIALLY EXPAND THIS TYPE OF SERVICE IN OTHER PORTIONS OF OUR DISTRIBUTION SYSTEM." }, { "addresseeAcronym": null, "addresseeOrganizationType": "P-Private Industry", "isFromNtsb": false, "communicationDate": "1992-03-26", "communicationType": "Official Correspondence", "communicationContents": "UGI MET WITH CITY OF ALLENTOWN REPRESENTIATIVES ON 1-29-92. THE MEETING WAS PRODUCTIVE AND BOTH PARTIES AGREED TO APPROACH THE PA. ONE CALL SYSTEM (POCS) AS A POTENTIAL RECIPIENT AND DISSEMINATOR OF INFORMATION REGARDING UNDERGROUND VOIDS WITHIN THE CITY. UGI HAS HAD PRELIMINARY DISCUSSIONS WITH POCS CONCERNING THIS SERVICE. BECAUSE POCS IS RENEGOTIATING ITS OUTSIDE VENDOR CONTRACTS AT THIS TIME, FINAL AGREEMENT WOULD HAVE TO WAIT UNTIL AFTER 5/31/92. UGI AND THE CITY OF ALLENTOWN WILL PURSUE THIS POTENTIAL SOLUTION AT THAT TIME." }, { "addresseeAcronym": null, "addresseeOrganizationType": "P-Private Industry", "isFromNtsb": false, "communicationDate": "1993-02-25", "communicationType": "Official Correspondence", "communicationContents": "THE CITY OF ALLENTOWN AND UGI HAVE AGREED TO USE THE PENN. ONE CALL SYSTEM AS THE RECIPIENT AND DISSEMINATOR OF INFORMATION REGARDING SINKHOLES WITHIN THE CITY OF ALLENTOWN." }, { "addresseeAcronym": null, "addresseeOrganizationType": "P-Private Industry", "isFromNtsb": true, "communicationDate": "1992-07-08", "communicationType": "Official Correspondence", "communicationContents": "THE SAFETY BOARD UNDERSTANDS THAT UGI HAS MET WITH CITY OF ALLENTOWN AND PENNSYLVANIA ONE CALL SYSTEM REPRESENTATIVES ON SEVERAL OCCASIONS TO DISCUSS THE ISSUE OF UNDERGROUND VOIDS." }, { "addresseeAcronym": null, "addresseeOrganizationType": "P-Private Industry", "isFromNtsb": true, "communicationDate": "1993-04-16", "communicationType": "Official Correspondence", "communicationContents": "THE BOARD UNDERSTANDS THAT UGI & THE CITY OF ALLENTOWN HAVE AGREED TO USE THE PENNSYLVANIA ONE CALL SYSTEM AS THE RECIPIENT & DISSEMINATOR OF INFO REGARDING SINKHOLES WITHIN THE CITY OF ALLENTOWN. BASED ON THIS INFO, P-91-16 HAS BEEN CLASSIFIED \"CLOSED--ACCEPTABLE ACTION.\"" }, { "addresseeAcronym": null, "addresseeOrganizationType": "P-Private Industry", "isFromNtsb": true, "communicationDate": "1992-01-28", "communicationType": "Official Correspondence", "communicationContents": "" } ] } ], "jurisdiction": "US" } ```