# NTSB Safety Recommendation Letter P-77-004

- **operation:** document
- **citation:** P-77-004
- **title:** NTSB Safety Recommendation Letter P-77-004
- **source type:** guidance
- **agency:** National Transportation Safety Board
- **status:** guidance
- **official:** true
- **published on:** 1977-06-08
- **effective on:** 1977-06-08
- **summary:** Official NTSB transmittal letter for safety recommendation P-77-004, issued 1977-06-08.
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- **source url:** https://www.ntsb.gov/safety/safety-recs/recletters/P77_4.pdf
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:j ;' i _jj' ,~/ ', i i NATIONAL TRANSPORTATION SAFETY BOARD WASHINGTON, D.C. ISSUED: June 8 , 1977 Director Materials Transportation Bureau Department of Transportation Washington, D . C . 20590 SAFETY RECOMMENDAT l O N ( S ) P-77-4 At 2 p.m., on August 8, 1976, a gas explosion destroyed a house at 1127 Oak Street, Allentown, Pennsylvania. The gas migrated from a break in a 4-inch cast-iron main under the street, through loose soil under a concrete sidewalk, and into the building through cracks and openings in its foundation. I-/ At 2:26 p.m., another house exploded across the street from the site of the first explosion. The front brick wall collapsed into the street and trapped two firemen. The street then caved in directly in front of the trapped fire- men. The cast-iron gas main within the sinkhole broke into several pieces; flames from the broken main were more than 10 feet high and hampered rescue of the trapped firemen. Two firemen were killed, 14 persons were injured, 4 build- ings were destroyed, and several buildings were damaged. The UGI Corporation is conscious of the sinkhole phenomenon which is a problem in Allentown, Pennsylvania. It has considered several experimental methods of locating sinkholes under cast-iron gas mains. Equipment manufacturers of "downward-looking'' radar have offered to make some equipment modifications and conduct a demonstration in Allentown to see if sinkholes under pavements and in the vicinity of underground utilities - 11 For more detailed information on this accident read Pipeline Accident Report, UGI Corporation, Natural Gas Explosions and Fires, Allentown, Pennsylvania, August 8, 1976, NTSB-PAR-77-2. 20488

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- 2 - can be successfullv located. Recent advances i n rada technology may have developed t h i s ca so, it w i l l save the time and money t required i n basic research t o develop a new subsurface electromagnetic pulse radar concept capable of detecting sinkholes from 1 t o 100 f e e t deep. The National Transportation Safe t h a t U G I "Expedite, i n conjunction w i the development of a survey u n i t t h a t detect the location of sinkholes i n the v i c i n i t y of cast iron gas mains. 'Downward-looking' radar equipment shou be investigated as one possible means of surveying fo sinkholes. ' I Therefore, the National Transpor recommends t h a t the Office of Pipelin the Materials Transportation Bureau: Encourage, coordinate, and monitor development of equipment which could be used t o detect the location of sinkholes i n the v i c i n i t y of underground u t i l i t i e s . (Class 111, Longer Term Followup) (P-77-4) TODD, Chairman, BAILEY, Vice Ch and HALEY, Members, concurred i n the By: Webster E. Todd, Jr. Chairman I
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