Crews failed to relocate pressure-sensing lines from an old cast-iron distribution main during a mid-September Columbia Gas pipeline replacement, igniting a series of explosions and fires north of Boston, according to a preliminary report by federal investigators. The mistake resulted in one death, 25 injuries and 131 damaged structures in Lawrence, Andover and North Andover on Sept. 13.
The contracted work in South Lawrence being overseen by a Columbia Gas inspector involved tying in a plastic distribution main and retiring an early-1900s cast-iron, low-pressure distribution main. The National Transportation Safety Board report notes the work package did not specify the location of sensing lines or require the relocation that would have ensured the regulators were sensing actual system pressure. “Once the contractor crews disconnected the distribution main that was going to be abandoned, the section containing the sensing lines began losing pressure,” the report says. “As the pressure … dropped about 0.25 inches of water column (about 0.01 psig), the regulators responded by opening further, increasing pressure in the distribution system.”
The report notes that Columbia’s monitoring center in Columbus, Ohio, received two high-pressure alarms minutes before the disaster but “had no control capability to close or open valves.” A Columbia Gas controller reported the high-pressure event to the Meters and Regulations group in Lawrence at 4:06 p.m., before the first 911 call five minutes later. Columbia shut down the regulator by 4:30 p.m. and “critical valves of the involved natural gas distribution system were closed by 7:24 p.m.,” the report says. The utility then began shutting off residential meters.
The Massachusetts Dept. of Public Utilities ordered a moratorium on Columbia Gas work, “except for emergency and compliance work, across the company’s entire service territory,” until at least Dec. 1.
Columbia Gas says all cast-iron and bare-steel piping in the affected neighborhoods will be replaced by Nov. 19 due to system integrity concerns. “The new system will consist of high-pressure plastic mains with regulators at each service meter to reduce the line pressure from the main to the required pressure,” the utility notes.
In a separate incident on Oct. 8, approximately 300 homes in Woburn, Mass., lost power. National Grid shut off gas meters following the inadvertent overpressurization of the natural gas line while performing routine maintenance on a regulator station, according to a National Grid spokeswoman. “The crew quickly recognized the error and within minutes, reduced the system to normal operating pressures,” she says. As of Oct. 11, gas service had been restored to all but a few homes.
Following that incident, DPU issued a moratorium on all National Grid work except for emergency and compliance work, across the utility’s entire service territory pending the results of a review of National Grid’s safety practices. DPU also required National Grid to have an inspector on hand for all work that could lead to abnormal pressurization until its review is complete. DPU will hire an independent evaluator to conduct a statewide examination of the safety of the state’s natural gas distribution system.
Massachusetts’ woes have heightened natural gas concerns across New England. Rhode Island and Maine are reviewing their natural gas safety measures.