Feds Release Initial Report on San Bruno Explosion

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The National Transportation Safety Board today released its preliminary report on "Accident No. DCA10MP008"-- the San Bruno PG&E pipleline explosion and fire in plain English.

The brief document offers a telling glimpse as to how Sergeant Joe Friday would conduct a review of a massive inferno that engulfed an entire neighborhood. No, you won't find any damning assignments of blame heaped upon PG&E here -- but you do find a few interesting things.

• Prior to the blowout, an electrical interruption cut power to the regulating valve for the ill-fated Line 132. As a result, the valve moved from "partially open" to "full open." Still, the pressure of gas flowing through the pipe apparently never exceeded the safety limit of 400 pounds per square inch -- though it got awfully close.

• "The examination revealed that the ruptured segment was 27 feet 8 inches long at its longest length, and consisted of a pipe section and four smaller pipe pieces (pups) between 3 feet 8.5 inches and 3 feet 11 inches long (pups are numbered one through four from south to north)."

 The following laboratory work on the pipe has been completed:

• Written documentation, photo documentation and visual inspection of the pipe.
• Removal of the asphalt coating from outside of the three pipe segments in preparation for non-destructive examination work.
• Radiography of the girth welds and select seams.
• Microbiological testing of the pipe surface (samples currently being analyzed).
• Ultrasonic wall thickness measurements.
• Magnetic particle inspection of welds and seams.
• 3-D laser scanning of the pipe pieces for a digital dimensional record of the evidence.
• Measurement of the longitudinal and circumferential pup dimensions.
• Removal of key fracture surfaces from the ruptured segment for further laboratory examination at the NTSB materials lab in Washington.

The following additional work is currently ongoing:

• Precision cleaning of the fracture surfaces on the pieces cut from the ruptured pipe segment.
• Hardness and microhardness testing.
• Optical fractographic analysis and photodocumentation of the fracture surfaces on the pieces cut from the ruptured pipe segment.
• Preliminary scanning electron microscopy of the fracture surfaces on the pieces cut from the ruptured pipe segment

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