Author(s): Angelo Verzoni. Published on November 1, 2018.

Focus on Gas

Gas explosion, fires rock Massachusetts communities as NFPA considers new requirements for residential gas detectors


A series of natural gas-fueled fires struck communities in Massachusetts in September, just as NFPA was considering a new standard on residential gas detectors.

On September 13, a string of gas fires, including one explosion, occurred in the state’s Merrimack Valley region, about 25 miles north of Boston, killing a teenager, injuring 25 others, and destroying or damaging dozens of homes. The incidents, more than 60 in all, occurred after the pressure in pipes delivering natural gas to residents in four communities spiked dramatically, according to the National Transportation Safety Board (NTSB).

The NTSB said this month that a faulty plan to replace aging gas pipes caused the pressure spike, The New York Times reported. “The company had approved the plan to replace century-old, cast-iron pipes, which had sensors to monitor pressure,” according to the Times. “But disconnecting the old system disabled the gauges, and the full flow of high-pressure gas into the system—without an accurate read of how high it was—caused the explosions in Lawrence, Andover and North Andover.” While the gas fires were generally reported as explosions, Guy Colonna, NFPA’s senior director of engineering, explained that the technical definition of an explosion requires the rupture of a container—“in these cases, the house,” he said. By that definition, he believes only one gas explosion occurred in the Merrimack Valley in September, while the other incidents should be classified as gas fires.

Coincidentally, the Merrimack Valley explosion and fires occurred as NFPA is considering new requirements for the installation, testing, and maintenance of gas detectors in homes, which would be modeled after existing NFPA requirements for carbon monoxide (CO) detectors, Colonna said. NFPA’s requirements for CO detectors were previously contained in NFPA 720, Installation of Carbon Monoxide (CO) Detection and Warning Equipment, but are now incorporated into NFPA 72®, National Fire Alarm and Signaling Code®.

NFPA received a request in early August from the American Gas Association to create a new standard to address the installation of residential gas detectors. “We’ve already concluded that such a document doesn’t exist, so there appears to be a need for it,” Colonna said, adding that it would include information on detectors for both natural gas, which is mostly methane, and propane. A new document could exist on its own or be incorporated into NFPA 72 as NFPA 720 was, Colonna said.

In an event like the Merrimack Valley incident, gas detectors could save lives. Colonna explained that for the combustion of natural gas in air to occur, the air needs to contain a minimum of 5 percent methane by volume and there needs to be an ignition source, such as a pilot flame in a gas stove or a light switch being flicked on. Detectors, which would sound when gas levels are much lower than that concentration, could alert occupants to get out.

Still, in incidents like these, a home might be so rapidly inundated with gas that detectors would do little good in alerting anybody inside the home before combustion occurs. The Merrimack Valley explosion and fires, for example, resulted from over-pressurization in gas lines transporting natural gas to homes. The pressure was reportedly 12 times higher than it should have been, meaning homes could have been flooded with the minimum concentration of methane needed for ignition before a detector even sounded, Colonna said. That’s why safety measures like pressure regulators exist to gradually reduce the pressure in gas lines as the gas approaches homes.

NFPA is currently soliciting input on the need for a gas detector standard. Information provided during this public comment phase will be considered by the NFPA Standards Council in April. If you or your organization want to comment on this proposed project or participate as a member of a technical committee, you can participate online.

ANGELO VERZONI is staff writer for NFPA Journal. Top Photograph: Getty Images