NTSB Safety Recommendation Letter P-80-014

Page 1Official PDFWASHINGTON, D.C. I S S U E D : March 5, 1980 Mr. G. H. Lawrence President American Gas Association 1515 Wilson Boulevard Arlington, Virginia 22209 SAFETY RECOMMENDATION(S) P-80-14 A t 10:25 a.m., c.d.t., on August 28, 1978, natural gas, which had escaped from 8 circumferential fracture in a socket heat-fusion coupling on a 2-in. polyethylene (PE) main, operating a t 40-psig pressure, migrated beneath a one-story house in Grand Island, Nebraska, exploded, and then burned. One person was injured; t h e house a t 2517 Apache Road was destroyed; and three adjacent houses were damaged. The gas was ignited by an unknown source. The 2-in. PE main was installed by a contractor for the Northwestern Public Service Company at a depth of 30 in. in a northsouth utility easement along a lot line, terminating just south of 2517 Apache Road. The main was inspected and tested on November 12, 1971. On December 6, 1971, a 4-in. acrylonitrile butadiene styrene (ABS) sewer service was installed at a depth of 52 in. perpendicular to and just beyond the end of the gas main and was inspected. On August 22-24, 1972, the gas main was extended 495 ft., inspected, and tested. The failed coupling was 23 in. south of the coupling used to tie in t h e extension. When the flexible, 2-in. PE gas main was exposed after the accident, it w a s laying on t h e semirigid, 4-in. ABS sewer pipe at a depth of 52 in. The coupling that failed was located a t a depth of 48 in. A 64-in. section of pipe, from a point 27 in. north of the sewer line to a point 37 in. south of the sewer line, was displaced from its original depth of 30 in. This sharp displacement, caused by the settling of improperly compacted backfill material, initiated a stress in the coupling which, in time, resulted in the circumferential fracture on the bottom of the coupling. The downward force which caused the displacement might have been prevented if the company had followed the construction procedures outlined in the Northwestern Public Service Company specifications for plastic pipe installation. Section 18, BACKFILL, of these specifications contains the following instructions: The Contractor shall make sure t h e line is properly supported by undisturbed earth in the trench bottom before the back-fill operation begins. Any voids under the line shall be filled by hand. Special care shall be taken to assure proper support at transition points from steel to plastic. Where bell-holes have been dug for any reason, the back-fill shall be compacted below the line before mechanical back-fill operation begins. 2839#

Page 2Other sections of the specifications make the contractor responsible for preventing damage t o the pipe during the construction process. Although Northwestern Public Service Company's construction procedures were in accordance with 49 CFR 192 Subpart G, apparently the procedures were not followed carefully during the construction of the main extension in August 1972. Therefore, the National Transportation Safety Board recommends that the American Gas Association: Notify its member companies of the facts and circumstances of this accident and urge them to review their actual operating practices for the supervision of the proper installation and proper support of plastic mains and services t o assure that they conform to established company procedures, related industry guidelines, and Federal regulations. (Class E, Priority Action) (P-80-14) KING, Chairman, DRIVER, Vice Chairman, McADAMS and BURSLEY, Members, concurred in the above recommendation. GOLDMAN, Member, did not participate. \#