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What Caused The Gas Explosions In The Merrimack Valley?

Gas Explosions
Multiple fire trucks from surrounding communities arrive on Sept. 13, 2018, in Lawrence, Mass., responding to a series of gas explosions and fires triggered by a problem with a gas line that feeds homes in several communities north of Boston.
Phil Marcelo/AP

There are more questions than answers in the wake of explosions and dozens of fires that leveled homes, prompted mass evacuations and cut electric power in Lawrence, Andover and North Andover. Mark McDonald is a gas expert who owns Nat Gas Consulting and spoke with WGBH News about his initial impressions. The following transcript has been edited for clarity.

Mark McDonald: It's pretty unprecedented. I have to say. I've investigated — me and my company, my experts — well over 100 gas explosions in the past six years. This is unprecedented. It's a major catastrophe. But it all points to an overpressurization of the system.

Essentially the gas pressure that arrives at our homes and our gas appliances is controlled. There is high pressure that is needed to move the gas from Texas, Tennessee, Canada, etc. to get it to Massachusetts. And what it entails is high, very high pressure gas. Hundreds, thousands of pounds. And it's reduced along the way once it gets to Massachusetts, and then once it gets to the gas company it's further reduced.

But then, once it gets to your neighborhood, there are what's called district regulator stations that are underground, most people don't even know they exist. And what it does is essentially control the gas from 100 pounds, sixty pounds or what have you. I don't know the exact pressure we're dealing with, but it reduces it down to a quarter of one pound which is again what we use safely in our homes. And it's critical. Because if for some reason the high pressure gas is mixed in with our typically low pressure lines, you have what we're seeing right now, which is multiple explosions and random fires. Not every home is affected. But you know the ones that are unfortunately had the perfect gas mixture and ignition source to cause an explosion and fire.

Mary Blake: That was going to be my question. The randomness of it. You see from the aerial views and one home is just engulfed while the other two next door are just sitting there.

McDonald: It's strictly by luck, and there's no better way to say it. And essentially for gas to explode it needs three things: It needs natural gas, it needs air and it needs an ignition source. But the gas has to be the right mixture. If it's too lean, there's not enough gas — like under five percent. Or if it's too rich, over 15 percent, if there's too much gas in the home, even with an ignition source it will not ignite. So my my guess is a lot of these homes have too much gas where even when they found the ignition source, it could not ignite.

Blake: This overpressurization — is this something that is clearly a case of human error?

McDonald: Well, we don't know that yet.

I mean it's possible it could be human error. It could be a contracting company could have been digging in the wrong area where they're not supposed to. It could be a mechanical failure. It could be failure to maintain the equipment that's designed to protect the public. You know, they're required to keep these district regulators as critical. As you can imagine — given what's taken place — they are critical devices that have to be inspected and maintained on an annual basis. So you know with that said, obviously we're going to be looking at this. I'm already involved in several of the homes we've already been retained on. One of things we're going to be looking for is to see the maintenance records. Was anyone digging near these? Was this an intentional act? We don't know. Especially in today's climate ... you can't rule anything out at this point, and it would be improper to do that until we start to put the pieces together in the puzzle.

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