Narural gas pipe explosion inUSA

A natural gas pipelines explosion in the US town of San Bruno has devastated the area.A news article mentions the following:
"The force of the explosion was large enough to level the area immediately around the blast’s epicenter. NTSB teams, as well as local investigators, are combing through the blast zone looking for evidence that will allow them to determine the cause. The primary problem with useful evidence in a fire investigation is the simple fact that much of it burns up during the event. Therefore, investigators have to look beyond the physical evidence to gain insight as to what really went wrong. Investigators are looking at the maintenance and safety records of the gas main in question, to see if red flags appear. They are also looking into the personal records of all individuals who worked on that particular section of pipe. This includes, drug problems and the general performance records of key individuals involved in the pipe’s maintenance.
Once the gas main has been designed and stringent regulations have been met, it’s up to qualified contractors to safely install the pipe. Lengths of pipe are specially welded together by trained pipe welders and this presents a potential problem. Anytime there is human interaction in the process of building something, the question arises; did that individual do their job correctly? The same holds true for the entire construction process. There have been numerous construction related disasters that were caused by insufficient materials, poor safety regulations and cost cutting. While there is no indication that these forces are at work here, the question still arises, was human error the driving factor in this accident? Mathematically, the odds are sadly in favor of human error".
Read the article in this link

How good and robust are your natural gas line inspection procedures? Are they getting implemented?