It was late in the evening when a massive explosion in Allentown, Pennsylvania destroyed an entire neighborhood block and killed five people, including an elderly couple asleep in their duplex.
The fireball that erupted in this blue-collar, downtown neighbourhood was caused by an aging underground gas line, according to local officials. Made of cast iron and originally installed in 1928, the line had been punctured, they said. Days after the tragedy, crews discovered a crack in the 12-inch main pipeline that travelled underneath the neighborhood.
In recent years, cast-iron pipelines have drawn the concern of the National Transportation Safety Board (NTSB). Cast iron was frequently used by utility companies because of its durability over long periods of time. However, the NTSB has issued previous warnings that similar cast-iron natural gas pipes were prone to decay and should be replaced. Today, most companies use plastic pipes to carry natural gas, although the federal Pipeline Safety Improvement Act of 2002 recommended using steel as well as plastic.
The utility that operates the line, UGI, was investigating the explosion when it discovered the crack in the pipe just a couple of blocks away from the gas explosion. The pipe lacked shutoff valves, a circumstance that fueled the fire that burned for hours after the initial explosion. UGI officials said that the company spends roughly $20 million each year replacing old cast-iron pipelines with plastic pipe, chiefly because plastic is not subject to the same corrosion as cast iron. There are some 63,000 miles of underground gas pipe running through Pennsylvania, and much of it still needs to be updated. It is unclear whether regulatory officials are requiring the pipes to be updated by a specific deadline, but Pennsylvania utilities are being closely scrutinized.