This does not, however, make for a reliable or safe industry. Every couple of days, a natural gas pipeline incident occurs in North America. Every four days, someone is injured. Every seventeen days, someone dies. 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.