Here's a pretty good analysis of what happened:

http://www.bu.edu/today/2018/gas-explosions-in-mass-can-happen-in-any-gas-system/

The Merrimack Valley is a fascinationg place to visit. It's north of Boston, near the Massachusetts-New Hampshire border. The towns of Lowell and Lawrence now have excellent museums that tell the story of the once-prosperous textile industry. The mills are almost all shut down now, turned into alternate uses or left abandoned. But there are lots on interesting old buildings to see, and I've wandered in the area a number of times.

One mill that didn't shut down, is Malden Mills in Lawrence. Even after a devastating mill fire, it survived by coming up with an insulating fabric called Polartec.

Our beloved Mudcatter Barry Finn lived not far away in Derry, New Hampshire.

-Joe-