25 Investigates: Gas company found at fault in past explosion events

25 Investigates: Gas company supplying Merrimack Valley involved in previous explosions that resulted in injuries

Columbia Gas had just issued a news release that it was upgrading gas lines Thursday in the same areas where explosions and fires ripped through parts of Lawrence, North Andover and Andover. The company has been involved in at least three other cases that caused injuries and damage.

In at least two past incidents investigators found workers at fault for accidents that caused injuries and millions of dollars in damages.

Disasters involving natural gas are far from unprecedented in Massachusetts but were not nearly as destructive and widespread as what happened Sept. 13.

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In 2012, explosions in Springfield injured 17 people and caused more than a million dollars in damage.

A state report determined that a technician with Columbia Gas punctured a line while investigating a complaint about the smell of natural gas.

In 2007, an explosion in Easton injured seven people and caused more than $2 million dollars in property damage.

25 Investigates talked to a National Pipeline Safety Expert in Washington State, Richard Kuprewicz, who said while it's too soon to speculate exactly what caused the incident that happened Thursday, the widespread nature of the disaster suggests there may have been a system-wide failure.

"For something this important, there's more than one level of safety. So if the first level fails, the second level protects you. More likely there's a breakdown there... the fact that it's like 20 houses says this is more of a system issue, Kuprewicz said.

25 Investigates left messages with Columbia Gas -- which has also operated as Bay State Gas -- for comment but has not received a response.

The National Transportation Safety Board has dispatched a "Go-Team" to investigate the cause.