But whatever cause eventually emerges, the dramatic event in Sissonville is set against a backdrop of several high profile natural gas accidents and a rapid increase nationally in gas pipeline mileage – even as federal oversight appears to lag.
"There are never enough inspectors at the state or federal level to adequately cover all the pipelines," says Rebecca Craven, program director at the Pipeline Safety Trust, a watchdog group based in Bellingham, Wash., that monitors energy pipelines of all types. "They can't physically spend enough time with each operator or pipeline to be able to do a thorough job and conduct regular inspections. They do what they can – enough to comply with their requirements."
The explosion at Sissonville adds to a previous tally of 80 small and large incidents this year involving just natural gas transmission lines, the big pipelines that ship huge quantities of gas from production areas to distribution hubs and population centers across the country, according to the Pipeline Hazardous Materials Safety Administration (PHMSA), a branch of the US Department of Transportation that inspects and regulates the nation's pipelines.
Of the 80 incidents, 38 were classified as significant, PHMSA data show. The accidents and fires reportedly caused seven injuries, no fatalities, and $44 million of damage.
Added to this year's accident tally for gas transmission lines were another 71 incidents with nine fatalities and 21 injuries involving natural gas distribution lines, the much smaller gas lines under lower pressure that bring gas directly to residential and commercial customers in and around major population centers, the PHMSA data show.