"A crew working to replace a gas line in Lawrence neglected to remove the pressure sensors from the old line, a preliminary report by the National Transportation Safety Board shows. That error would trigger a flood of high pressure through the system on Sept. 13 that resulted in fires, explosions and damage to more than 80 Merrimack Valley homes, several injuries and one death," according to a article published by MassLive.com.
"The NTBS released the preliminary report Thursday. Crews were working to upgrade the gas line system the day of the massive damage that occurred in Lawrence, North Andover and Andover and resulted in thousands being evacuated from their homes. A month later many remain without gas service."
"Before the over-pressurization of the gas line, a Columbia Gas contracted crew, that included an inspector from the company, was performing an approved pipe-replacement project at South Union and Salem streets in South Lawrence", says MassLive.com.
"The crew was working on a tie-in project where a new plastic distribution main was being installed to replace the cast-iron distribution main, according to the report."
"The distribution main that was abandoned still had the regulator sensing lines used to detect pressure in the system. The sensing lines provide input to regulators in order to control the system pressure, according to the NTSB" says the MassLive.com story.
"Once the distribution main that was no longer going to be in service was abandoned, the section with the sensors began to lose pressure, the report said."
"The system regulators opened wider, increasing pressure in the system."
"Since the regulators no longer sensed system pressure, they fully opened allowing the full flow of high-pressure gas to be released into the distribution system supplying the neighborhood, exceeding the maximum allowable pressure."
"The work package developed and approved by Columbia Gas did not "account for the location of sensing lines or require their relocation to ensure the regulators were sensing the actual system pressure," the NTSB report says." And as reported by MassLive.com.
"The system over-pressurization caused damage to 131 structures and at least five homes were destroyed in Lawrence, North Andover and Andover."
"Most of the damage was caused by fire ignited by gas-fueled applications"; and in the wake, some 8,600 homes and businesses were left without natual gas service.
To read the original MassLive.com article, go to: https://www.masslive.com/news/index.ssf/2018/10/columbia_gas_failed_to_relocat.html