NTSB Safety Recommendation P-76-017

NTSB safety recommendation P-76-017.

DETERMINE THE NUMBER OF SIMILAR PLASTIC PIPE COUPLING INSTALLATIONS IN THEIR FACILITIES, EXCAVATE AND INSPECT A STATISTICALLY REPRESENTATIVE SAMPLE OF THESE TO DETERMINE IF THEY HAVE BEEN INSTALLED CORRECTLY, TAKE REMEDIAL ACTION ON ANY DEFICIENT INSTALLATIONS FOUND DURING THE SAMPLING, AND BASED UPON THE RESULTS OF THE SAMPLING, INSTITUTE NECESSARY CORRECTIVE ACTION. (URGENT)

Priority: CLASS I

Overall Status: Closed - Acceptable Action

Issued Date: 1976-02-08

Adopted Date: 1976-04-29

Overall Date Closed: 1983-01-27

Synopsis: ON FEBRUARY 8, 1976, A HOUSE IN PHOENIX, ARIZONA, EXPLODED AND BURNED. OF TWO PERSONS WHO WERE HOSPITALIZED AS A RESULT OF THE ACCIDENT, ONE DIED.

Probable Cause: The National Transportation Safety Board's investigation of this accident disclosed that the natural gas at 39-psig pressure had leaked from the compression coupled connection of a 2-inch pipe appeared to have been inserted insufficiently through the gasket and into the coupling. Gas which leaked from this joint was trapped from above by heavily compacted soil; it consequently seeped into the house, where it was ignited by an unknown source. The 2-inch plastic pipe, which was installed in 1968 by the Arizona Public Service Company, was damaged by an excavator in 1969. The gas company repaired the leak by installing a 6-inch-ling compression coupling to connect each end of the severed 2-inch plastic pipe. The repaired section was wrapped with tape which extended 3 to 4 inches over the pipe on each side of the coupling.

Ntsbnumber: DCA76FP015

Report Number: None

Addressee Name: Arizona Public Service Company

Addressee Status: Closed--No Longer Applicable

Addressee Date Closed: 1983-01-27

Addressee Acronym: APS

Addressee Organization Type: P-Private Industry

Communication Date: 1982-11-12

Communication Type: Official Correspondence

Communication Contents: ARIZONA PUBLIC SERVICE COMPANY: IN FEBRUARY OF 1976, APS CONDUCTED AN ANALYSIS OF 28,000 UNDERGROUND INSPECTION REPORTS AND DETERMINED THAT THERE WERE APPROXIMATELY 482 PROBABLE LOCATIONS INVOLVING SIMILAR PLASTIC PIPE COMPRESSION COUPLINGS. WE COMPLETED A LEAK SURVEY OF ALL THESE LOCATIONS BY APRIL 18, 1976, AND DETECTED NO LEAKS ON COMPRESSION COUPLINGS. IN ORDER TO ESTABLISH A VALID SAMPLE TESTING PROGRAM, IT WAS DETERMINED THAT A REPRESENTATIVE EXPERIENCE COULD BE STATISTICALLY ACHIEVED BY INSPECTING AND TESTING 34 OF THE SUBJECT COUPLING INSTALLATIONS. SUBSE QUENTLY, APS EXCAVATED AND REMOVED 34 UNITS AND CONDUCTED SHOP TESTS ON EACH OF THESE. THE TESTING WAS COMPLETED 5/20/76, WITH THE RESULTS INDICATING THAT ONE SAMPLE LEAKED IN THE SHOP TEST WHEN TESTED IN AN UNRESTRAINED POSITION. THAT UNIT WAS NOT LEAKING IN A RESTRAINED POSITION IN THE FIELD. THE STATISTICAL ANALYSIS OF THE TEST RESULTS ESTABLISHED THAT THE POSSIBILITY OF FUTURE PROBLEMS WAS EXTREMELY SLIGHT. NONETHELESS, APS DECIDED, AT THAT TIME, TO COMPLETELY DISCONTINUE THE USE OF THIS TYPE OF COMPRESSION COUPLING AND INSTRUCTED OUR EMPLOYEES TO REMOVE ANY OF THESE COUPLINGS ENCOUNTERED IN THE FIELD.

Addressee Acronym: APS

Addressee Organization Type: P-Private Industry

Communication Date: 1982-10-05

Communication Type: Official Correspondence

Addressee Acronym: APS

Addressee Organization Type: P-Private Industry

Communication Date: 1983-01-27

Communication Type: Official Correspondence