NTSB: Mass. natural gas blast occurred after system was over-pressurized
The spectacular series of natural gas blasts and ensuing fires that leveled homes in the Merrimack Valley of Massachusetts, killing one person and injuring 21 others, occurred as work crews were in the process of updating the 118-year-old gas distribution system that serviced the area.
A preliminary report by the National Transportation Safety Board (NTSB) says the catastrophe occurred after high-pressure natural gas was released into a cast-iron, low-pressure distribution system that had been installed in the early 1900s.