The National Transportation Safety Board has released its final report on last year's deadly Merrimack Valley gas explosions.
The 73-page report issued says the probable cause of the overpressurization that led to the gas explosions on Sept. 13, 2018 was Columbia Gas' "weak engineering management that did not adequately plan, review, sequence, and oversee the construction project" that led to the abandonment of a cast iron gas main without first relocating regulator sensor lines to the new main.
Another contributing factor was that the gas distribution system was designed and operated "without adequate overpressure protection," the report says.
The NTSB report lays out a series of recommendations for the state and NiSource, the parent company of Columbia Gas, to prevent a similar disaster from happening again.
The Sept. 13, 2018 gas explosions killed 18-year-old Leonel Rondon and injured 25 others, set more than 100 homes on fire and displaced 8,000 people in Andover, North Andover and Lawrence.
Residents were forced out of their homes and into shelters as their homes and belongings burned in what one horrified fire chief described as "Armageddon." For months, Merrimack Valley homeowners lived in reception centers, trailers and hotel rooms as they awaited the approval to return home and start over.
Columbia Gas agreed to pay $143 million to settle all class action lawsuits in connection to the disaster.