NTSB Safety Recommendation Letter P-72-063 through P-72-068

Page 1Official PDFpressure of 20 p.s.i.g" to migrate under and into the affected house at 2109 Amanda Street. T h e distance between houses was large enough so that almost all.of the blast and en- suing fire were confined to 2109. The leaking gas from the four other failures posed a hazard, but Lone Star, forewarned by the explosion, was able to detect these breaks and repair them before additional accidents oc- curred. A review of the ASME guidelines, specifi- cally concerning heat fusion joints (849..394) and prevention of damage due to external load- ing or settling of backfill (849.52), indicates that although Lone Star complied with them in gen- e r a l , the guidelines were not implemented thoroughly enough to prevent the accident. L.one Star did not give proper consideration at the time of the system's installation to both the soil heaving problem and the planned construc- tion work on Amanda Street. came from a break in the ulastic service line which served the house across the street. i V. PROBABLE CAUSE . The National Transportation Safety Board determines that the probable cause of the explo- sion and fire was the ignition of an accumulation of natural gas which had migrated under a pres- sure of 20 ps.i.g. from a failed plastic service saddle-tapping nipple connection into the house. Contributing to the failure of the connec- tion were its improper installation, previously imposed load stresses which resulted from the repeated operation of heavy construction equip- ment over the connection, and heavy rainfall which caused the soil to exert pressure on the pipe. VI. E&CQ-U.M.END.ATIONS The National Transportation Safety Board IV. CONCLUSlONS Q recommends that: 1. The Office of Pipeline Safety of the De- The National Transportation Safety Board partment of Transportation: concludes that: Undertake a study in the field of heat 1. The Lone Star construction specifications fusion of plastics and, as a result of that for the installation of plastic pipe were not spe- study, issue regulations for the heat-fusion cific in detailing the type, size, and kind of rein- welding of plastic piping systems in 49 CFR forcing sleeve to be used in service saddle- Part 192, Fusion Welding, in as much detail tapping nipple fusion welds. as is contained in the existing welding speci- 2. The plastic gas distribution system which fication for steel piping systems. (Recom- suffered failures in this area was installed im- mendation No. P-72-63)" properly and was not adequately inspected dur- 2. The American Society of Mechanical ing construction. E.ngineers Gas Piping Standards Committee: 3. T h e newly installed gas distribution (a) Develop guidelines for the use of rein- system had been subjected to repeated loads and forcing sleeves at plastic service line-gas main stresses by the heavy equipment which had connections and incorporate them in the "Guide operated directly over it while widening the road for Gas Transmission and Distribution Piping and laying curbs and sidewalks. Systems." (Recommendation No. P-72-64). 4. The plastic service connection was weak- (h) Develop guidelines for the require- ened additionally by improper fusion and by an ments concerning reinforcement, special back- incorrect reinforcing sleeve. The connection fill, and tamping of mains and service lines failed under the stress applied to it by the rain- where their installation will be sub,jected to ex- soaked, heaving soil. ternal forces due to anticipated road, curb, or 5. The leaking gas which migrated up and sidewalk construction, as well as unstable soil seeped into the house at 2109 Amanda Street conditions. (Recommendation No. P-72-65), . .-....-.I =--.-..----- 7...---. ~ ... . . . . . . . . . . . . . ..-. ..---..- . . . . . . . . . . . . . . .#

Page 2.,. The Lone Star Gas Company: (a) Revise its plastic pipe construction specifications to include the specific type and sue reinforcing sleeve to be used with each type of service saddle-tapping nipple connection. (Recommendation No. P-72-66). (b) Educate its construction inspectors as to the necessity for correct installation of plastic piping systems. (Recommendation No. P-72-67). (c) Undertake a program acceptable to the Railroad Commission of the State ofTexas, to inspect on a random sample basis the plastic service line-gas main connections, similar to those at the accident site to determine the pre- sent condition of and the existing stress on the piping. The results of this program will deter- mine the action to be taken on the other instal- lations in the Lone Star system. Copies of these test results should be forwarded to the Railroad Commission of the State of Texas and the Office of Pipeline Safety of the Department of Trans- portation (Recommendation No. P-72-68). BY THE NATIONAL TRANSPORTATION SAFE.TY BOARD Is/ JOHN H. REED Chairman Is/ FRANCIS H. McADAMS Member Is1 ISABEL A. BURGESS Member Is/ WILLIAM R. HALEY Member Louis M. Thayer, Member, was not present and did not participate in the adoption of this report. December 13, 1972 .#