MERRIMACK VALLEY GAS EXPLOSIONS: Why the NTSB is involved

Thousands are out of their homes in the Merrimack Valley after explosions rocked at least 70 homes across Lawrence, Andover, and North Andover.

Authorities believe over-pressurized gas lines are to blame for explosions and fires that ignited chaos Thursday afternoon. Firefighters struck ten alarms as they battled the fires, with 18 raging at once.

Residents in Andover and North Andover and those who live in South Lawrence were ordered to evacuate.

Gas was turned off to 8,000 homes and more than 15,000 people in the Merrimack Valley are without power Friday morning.

Several injuries were reported. Leonel Rondon, 18, was killed when a chimney from a house explosion fell on his car while he was sitting in a driveway on Chickering Road in Lawrence.

On Thursday night, the National Transportation Safety Board announced that it would be sending a "Go-Team" to Lawrence.

The purpose of the "Go-Team" is to begin investigating a major accident at the scene as quickly as possible.

But why is the NTSB involved?

The NTSB has a special group of staff that make up the Pipeline and Hazardous Materials Division. According to the NTSB:

"The Pipeline staff investigates accidents occurring during the transport of natural gas or other hazardous liquids, such as gasoline or propane, through pipeline systems and accidents in which public safety is threatened by the release of hazardous substances. The Division investigates all pipeline accidents in which there is a fatality, substantial property damage, or significant environmental impact."

NTSB Chairman Robert Sumwalt held a media availability before the "Go-Team" departed for Lawrence.

The team is expected to arrive in Lawrence around noon Friday. Once the team arrives, they will meet with the incident commanders. Investigators will be looking at the design of the pipeline and any maintenance being done. The team will do a review of Columbia Gas and the safety plan of the pipeline operator.

In 2010, the NTSB investigated a pipeline explosion in San Bruno, California.

Officials say they have been in contact with local authorities and will be very involved from here on out.

Cox Media Group