# NTSB Safety Recommendation Letter P-77-005

**Citation:** P-77-005  
**Type / status:** guidance / guidance  
**Agency:** National Transportation Safety Board  
**Effective:** 1977-06-08  
**Published:** 1977-06-08

Official NTSB transmittal letter for safety recommendation P-77-005, issued 1977-06-08.

## Document text

Page 1
I.: ' I - - J ,/ " .;/ ;j' 1 , ) i ,/ I;, . i I8 NATIONAL TRANSPORTATION SAFETY BOARD WASHINGTON, D.C. ISSUED: ,June 8, 1977 --------_------__I______________________ Forwarded to: Mr. Lowell Elder Chairman American Society of Mechanical Engineers Gas Piping Standards Cornittee P-77-5 United Engineering Center 345 East 47th Street ----------L------------------------------ New York New York 10017 SAFETY RECOMMENDAT I O N (S) A t 2 p " m " , on August 8 , 1 9 7 6 , a gas explosion destroyed a house a t 1 1 2 7 Oak S t r e e t , Allentown, Pennsylvania. The gas migrated from a break i n a 4-inch cast-iron main under the s t r e e t , through loose s o i l under a concrete sidewalk, and i n t o the building through cracks and openings i n i t s foundation. - 11 A t 2 : 2 6 p " m . , another house exploded across the s t r e e t from the s i t e of the f i r s t explosion. The f r o n t brick wall collapsed i n t o the s t r e e t and trapped two firemen. The s t r e e t then caved i n d i r e c t l y i n front of the trapped f i r e - men. The cast-iron gas main within the sinkhole broke i n t o several pieces; flames from the broken main were more than 1 0 f e e t high and hampered rescue of the trapped firemen. Two firemen were k i l l e d , 14 persons were injured, 4 build- ings were destroyed, and several buildings were damaged. The f i r s t break i n the 4-inch cast-iron low-pressure gas main occurred approximately one-half hour before the first explosion. The break was 314-inch wide because p a r t of the broken main was sagging over a sinkhole i n the s t r e e t . The opening i n the main was equivalent t o the discharge of a 3-inch pipe a t approximately 8 inches W . C . pressure. The gas migrated through loose s o i l under s o l i d pavement t o the basement of the two houses t h a t exploded 26 minutes apart from separate sources of ignition. 1/ For more detailed information on t h i s accident read - Pipeline Accident Report, U G I Corporation, Natural Gas Explosions and F i r e s , Allentown, Pennsylvania, August 8 , 1 9 7 6 , NTSB-PAR-77-2. 2048A

Page 2
Therefore, the National Transportation Safe recommends that the Gas Piping Standards Committ American Society of Mechanical Engineers: Develop guidelines t o a s s i s t operators d emergencies t o promptly i s o l a t e leaking se pipe i n a low-pressure system. (Class 111, Longer Term Followup) (P-77-5) TODD, Chairman, BAILEY, Vice Chairman, and HALEY, Members, concurred i n the above recommendatio

## Provenance

- Official: Yes
- Source: <https://www.ntsb.gov/safety/safety-recs/recletters/P77_5.pdf>
- Source ID: `ntsb-transmittal-letters`
- SHA-256: `2c16e50cae3ba1032b45f783492d2b648952a739aee7f8adca17e50f87569042`
- Retrieved: 2026-08-20T04:55:47.446Z
- Exported: 2026-08-26T11:39:40.743Z
- Document slug: `ntsb-transmittal-letter-p77-5`

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