San Bruno: The Investigation of the Pipe

Sunday, Sep 12, 2010  |  Updated 2:51 PM PDT
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These are the first pictures of the damage left by a massive <a title=PG&E pipeline explosion in San Bruno." />

These are the first pictures of the damage left by a massive PG&E pipeline explosion in San Bruno.

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The natural gas explosion that preceded a massive fire around  Crestmoor Canyon in San Bruno launched a 28-foot section of pipe a distance  of about 100 feet from underground out onto the street, the vice chairman of  the National Transportation Safety Board said Saturday.

      The explosion also created a crater 167 feet long and 26 feet  wide, NTSB Vice Chairman Christopher Hart said.
     
"This really emphasizes the magnitude of what occurred here," Hart  said.
     
The depth of the crater is unknown because the soil is unstable on  the floor of the hole, making it unsafe for a person to go in to measure,  Hart said.
     
At about 6:15 p.m. Thursday, a 30-inch PG&E steel gas transmission  pipeline ruptured, causing a massive explosion and fire that officially  killed four people and hospitalized more than 50 others.
     

Saturday was the first full day of investigation for the NTSB.  Ravindra Chhatre, the lead NTSB investigator for the San Bruno explosion and  fire, has more than 30 years experience with pipelines, Hart said.
     
Investigators found multiple seams on the section of pipe, Hart  said. The NTSB initially reported that the section of pipe was seamless, he  added.
     
"Longitudinal seams" found on the pipe means it started as a flat  piece of metal that was curved and welded, Hart said.
     

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The pipe also has "circumferential welds," meaning that section  was made of smaller segments of pipe, Hart said.
     
"So that opens another avenue of investigation, namely to  determine why that segment had sub-segments," Hart said.
     
Welding does not automatically mean that segment of pipe had  undergone repairs, Hart said. Segmented pipe is more expensive than pipe not  welded together from smaller pieces, he added.
     
"There are lots of reasons to have segmented pipe like this," Hart  said.
     
It's too early to tell if the pipe was corroded, Hart said. It's  also unknown how deep underground the pipe was at the time of the explosion,  he added.
     
There was no automatic shutoff valve on the pipe, Hart said. The  locations of two manual shutoff valves on either end of the pipe are unknown,  he said.
     
PG&E has provided the NTSB with information on the locations of  other pipelines in the area, Hart said. The date of the last PG&E inspection  of the pipe is unknown, he added.
     
The Pipeline and Hazardous Materials Safety Management  Administration classifies the pipe as "Class 3", which refers to "density of  population in the vicinity of the pipe," Hart said. Class 3 pipes are in  areas with more than 47 homes per linear mile of pipe within 220 yards on  either side of the pipeline, Hart said.
   
 Large pipelines in residential areas usually means the pipeline  was built before the area was heavily populated, Hart added.
     
The gas in the pipe was odorized to make it detectable to the  human nose, Hart said. Witnesses have reported allegedly smelling gas in the  area before the explosion.
     
The NTSB is asking anyone with information about the explosion to  email sanbruno@ntsb.gov.
     
The California Public Utilities Commission has established a  toll-free number and e-mail address for anyone who noticed the smell. People  can call (800) 789-0550 or send an e-mail to SBFire@cpuc.ca.gov if they  smelled the gas.
     
"Anybody who wants to report information of any type that may be  pertinent to this accident, whether they've been interviewed or not, we would  welcome them to provide further information," Hart said. "It's very important  for us to get information from every source that we can."
     
Hart has said he estimates it would be 14 to 18 months before NTSB  issues a final report and recommendations. Lt. Gov. Abel Maldonado said in a  statement Saturday that timeline was "unacceptable."
     
The NTSB has instructed PG&E, the Pipeline and Hazardous Materials  Safety Management Administration, the California Public Utilities Commission  and other organizations to not entertain requests from media, Hart said.
     
"We are the sole source of information about this accident," Hart  said.
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