The Woburn incident has heightened tension in the Merrimack Valley region still reeling from the series of fierce gas explosions and fires that ravaged three communities north of Boston on Sept. 13, left, caused one death and injured at least 25 people.

On Oct. 8, the odor of natural gas from a Lawrence elementary school roof led to the second evacuation of students in five days. While Lawrence officials and Columbia Gas say the elementary school incidents, involving a leaky rooftop unit since shut off, are unrelated to the Sept. 13 incident, recent emergencies have the Boston region on high alert. Neighboring states, including Maine and Rhode Island, are reviewing natural gas safety measures.

Lt. Tim Donovan of the Woburn Police Dept. said the department was working with National Grid crews going home to home to restore gas power and providing a command center. National Grid expects to restore power to all homes by Oct. 11.

Meanwhile, a spokesman for the Massachusetts Dept. of Public Utilities says the department issued a moratorium on Oct. 8 on all Columbia Gas and National Grid work except for emergency and compliance work, across the company’s entire service territory pending the results of a review of the two utilities' safety practices.

“In addition, the department is requiring National Grid to have an inspector on location for all work that could lead to abnormal pressurization until this review is complete. Separately, the department is in the process of hiring an independent evaluator to assess, out of an abundance of caution, the safety of pipeline infrastructure throughout Massachusetts.”

The National Grid statement notes there is no apparent damage to the pipeline system for the Woburn homes and pressure-control devices at each property function as an extra safety measure to limit the flow of gas to safe and normal levels. “The gas was shut off as a precaution and to confirm there is no damage to the system,” the statement notes.

The same day Sen. Elizabeth Warren (D-Mass.) tweeted that “300 Woburn households are without gas service tonight – while @nationalgridus continues to lockout 1,200 skilled @steelworkers who could be helping. Massachusetts families need this lockout to end now.”

National Grid has been relying on replacement workers and supervisors to conduct routine gas work since union 1,250 workers were locked out in late June The union refused a new contract that traded the traditional pension plan current employees receive for higher health care costs and a 401 (k) retirement package for new hires.

Marcy Reed, the president of National Grid in Massachusetts, on Oct. 9 reportedly defended the utility’s use of replacement workers saying the supervisor who let too much pressure into the gas line was an employee with decades of experience. She added that replacement workers and supervisors were slowly adding pressure to the pipes on Oct. 9 and testing the system before turning gas back on to the homes. 

Warren and Sen. Edward Markey (D-Mass.) in a joint letter on Oct. 5 demanded answers from Columbia Gas of Massachusetts and its parent company NiSource on critical deficiencies in company safety and response plans for a disaster like what occurred in the Merrimack Valley on Sept.13. “

After reviewing key company safety, operations and response plans, the Senators found that Columbia Gas did not properly contemplate the possibility that a disaster like this could occur, did not have sufficient safety measures in place to prevent a disaster, and was not prepared to respond,” said Sen. Markey in an Oct. 5 statement.

Columbia Gas announced a construction restoration project plan on Oct. 2 that includes the deployment of nearly 200 construction crews as part of a combined workforce of about 3,000 employees and contractors. The project aims to complete work by Nov. 19, installing gas main lines and service lines, as well as installing and testing gas meters that measure and regulate gas flow to homes and businesses. So far, 20 miles of pipeline and 1,075 service lines have been replaced, according to Columbia Gas. A total of 5,800 Columbia Gas customers were affected by the disaster.

"We’ve been working with partners at every level of government, with our first responders and departments of public works in our planning efforts to rebuild the system," said Joe Albanese, Columbia gas chief recovery officer. “Our early actions, supported by the National Guard, helped meet some immediate community needs. Now we turn to our current effort in support of the primary mission - to restore gas service to homes and businesses.”

The National Transportation Safety Board (NTSB), says its full investigation into the cause of the Sept. 13 incident could take up to two years.