explosion, finding block after block of ruins where their homes once stood. lee cow an is live for us in san bruno. good morni. reporter: again, the investigation into what caused the explosion is taking two tracks. one is the state and local level, the other is the federal. investigators here have now ordered the owner of the pipeline to investigate all their pipelines paying special attention to all those high pressure lines that go near neighborhoods. pg&e has said that that was an ageing pipeline. they were going to replace it, but still don t know what caed the explosion. that is where the ntsb is now stepping in. they re taking this giant section of the pipe that blew away during the explosion. they re wrapping it up, shipping it to washington to figure out what caused the rupture. was it corrosion, fatigue?
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