III. NTSB INVESTIGATION TO DATE

The NTSB is a federal safety agency charged with the responsibility to investigate and determine the causes of various kinds of accidents in the United States, including accidents involving natural gas pipelines. Since September 10, 2010, the day after the San Bruno pipeline rupture, the NTSB has been conducting an on-going investigation of the cause of this tragedy. The Commission is a participant in the NTSB investigation, through the Commission's Consumer Protection and Safety Division ("CPSD"). The CPSD investigators arrived at the accident scene on the evening of September 9, 2010, and have participated actively and continue to participate in the NTSB investigation.

On September 10, 2010, NTSB representatives arrived at the site of the San Bruno gas pipeline rupture and commenced their investigation. The NTSB describes its immediate actions in this way:

When the NTSB arrived on scene on September 10, the investigation began with a visual examination of the pipe and the surrounding area. The investigators measured, photographed, and secured the approximately 28-foot-long ruptured pipe segment. On Monday, September 13, the ruptured pipe segment and two shorter segments of pipe, cut from the north or south sides of the rupture, were crated for transport to an NTSB facility in Ashburn, Va., for examination. (NTSB Preliminary Report, p. 2, Appendix A).

Later NTSB examination showed that the 27 foot 8 inch segment of pipe that had been hurled from the ground by the rupture consisted of four joined "pup" pipes, and one "long joint" pipe, all welded together by circumferential or "girth" welds. NTSB examination also appears to demonstrate that all components of the 28 foot ruptured pipe were longitudinally welded (NTSB January 21, 2011 Materials Laboratory Factual Report, p.2, Appendix C).

On January 3, 2011, the NTSB publicly issued what the agency characterized as an "urgent" public Safety Recommendation as a consequence of information gleaned from its ongoing investigation into the San Bruno explosion. The NTSB Safety Recommendation is described in greater detail below, and is the principal basis for this Order Instituting Investigation.

On January 21, 2011, the NTSB published Report No. 10-119, entitled "Materials Laboratory Factual Report" (Appendix C). The January 21 report described the technical examination and testing of the ruptured pipe and of appurtenant pipes. The report concluded that the ruptured pipe and the pipe segments were characterized by longitudinal welded seams, of which at least some segments "showed various defects including lack of penetration, incomplete fusion, slag inclusion, porosity, and undercutting," and girth welds that "exhibited various defects including lack of penetration, incomplete fusion, burn through, slag inclusion, crack, porosity, undercutting, and excess reinforcement." (NTSB Factual Report, p. 6, Appendix C.)

The NTSB's January 21, 2011, report also concluded that the fracture in a longitudinal pipe seam "initiated in a manner consistent with ductile overstress from the root of the weld." (NTSB Factual Report, p.10, Appendix C.) The report also identified factual findings pertaining to the circumferential welds. The January 21 report did not identify the force or forces that "overstressed" welds, and did not explicitly identify the order of weld failures or whether a particular failure caused or contributed to another failure. The Commission anticipates that a later NTSB report or reports on the root cause of the September 9, 2010 rupture may provide such information and conclusions. The Commission notes that the NTSB has scheduled a three-day public hearing on the San Bruno rupture on March 1-3, 2011, as part of the NTSB's investigation into the root cause of the San Bruno explosion. The NTSB has not indicated when its final report on the root cause of the explosion will be issued.