Natural gas pipelines are grouped into two categories. Transmission lines are the big ones that run from remote gas fields to urban centres. Distribution lines are the smaller ones that run down our streets and into our homes. The transmission industry makes a big effort to avoid being associated with the injury rate of distribution lines. However, as urban areas have expanded into what was once countryside, in the last forty years, transmission lines are now more prevalent in populated areas, and the risk to humans increases accordingly.
Regulations cover things like steel strength, wall-thickness, testing schedules.
What the regulations cannot cover is the guy with the backhoe, the farmer on his tractor, the ship dragging anchor, the earthquake. The industry of course finds this convenient, because they can absolve themselves of responsibility for whatever occurs, without it actually getting in the way of their business or their profits. In 1996 an area on the western slope of Sumas Mountain in Washington State washed away. A natural gas pipeline that ran across the slope, lost its support and broke. In June of 1999, a pipeline broke in Bellingham Washington.