Following the intense gas-transmission line fire that started last night at San Bruno, CA: a local article is here.
This article from the San Jose Mercury says it was an 8-alarm fire and the radiant heat was enough to ignite furniture through a plate glass window.
In a Time blog on "natural gas industry under new scrutiny," there's a map of the pipelines feeding into CA.
Natural gas is a rare energy source in that (until the hydro-fracking controvery, anyway) it has generated little concern on a national level although there have been some catastrophic events on a local scale and a number of regional controversies about proposed LNG terminals.
Big gas-line breaks are statistically rare but release a great deal of energy.
Causes are usually construction machinery damage or corrosion. One of the worst US gas-line blasts caused was due to untended corrosion and caused fatalities at a camping site on the Pecos River near Carlsbad, NM, in 2000. The NTSB report on that one is here.