The National Transportation Safety Board last week released the first of its factual reports on the natural gas pipeline rupture and explosion that killed eight people in San Bruno, Calif., on September 9, 2010.

The Metallurgical Group Factual Report documents the facts related to the as-received visual and non-destructive examination and fractography of the ruptured 30-inch diameter steel pipe segment. According to an NTSB press release, the report does not include any analysis of the factual information contained in it; it is one of a series of factual reports that the NTSB is developing during the course of the investigation.

Additional reports on operations, human performance, survival factors, fire scene, and meteorology, will be released on the first day of the fact-finding investigative hearing that the NTSB will hold in Washington, DC, in March. The hearing, originally scheduled for two days, has been expanded to three days (March 1-3) due to the number of issues to be examined.

Analysis of the accident, along with conclusions and a determination of probable cause, will come at a later date when the final report on the investigation is completed.