which owns the line, said the pipeline, quote, ranks in the top 100 highest risk line sections, adding, the risk of failure is unacceptably high. the document was part of a budget request to replace the line. >> this raises the question of what pg&e knew and when they knew it, and whether better safety procedures could have avoided this horrible tragedy. >> reporter: san bruno's mayor was unaware of the risk assessment. is that troubling to you? >> the whole thing is. >> reporter: you can see the pipe right there that blew, investigators from the ntsb are taking measurements and pictures of it. it's the focus of their investigation. later, investigators will ship the damaged section of pipe to a lab in washington for tests to help determine whether sewer line work in the neighborhood could have been a factor. >> that's one of the things that that will help ascertain, because we will be able to determine, was the pipeline