Dozens of houses in Massachusetts have exploded. A gas expert weighs in. – The Atlantic Ocean

"I can not imagine any other explanation for this event than a flush of gas under pressure," says Jackson.

If local pipelines are indeed suddenly flooded with high-pressure gas, says Jackson, this could lead to an explosion in one or two ways. First, the pipes themselves could explode. Secondly, and more likely, according to Jackson, excessive pressure could have caused gas to leak from pipes and valves and into houses where it could be ignited by a pilot flame and entire buildings went up in flames.

In most cases, according to Jackson, such a rapid pressure would be caused by a failure of a valve separating high and low pressure lines. Regarding what would lead to such a failure, Jackson says, "someone may have made a mistake." Leave a split open to turn the wrong valve. "Human errors are the most common source of gas blasts."

The Columbia Gas website announced an improvement campaign a few hours before the explosions started, but there is no evidence yet that the explosions are linked to pipeline updates or failed repairs. (A Columbia Gas spokesman did not respond to a request for comment)

A gas coil can also occur if older valves are leaking or breaking. In 2015, Jackson and his colleagues discovered that cities such as Cincinnati, which replaced their aging pipelines, had 90 percent fewer gas leaks a mile than older cities such as Boston relying on older cast iron tubes. Across the country, Jackson says, many local pipelines are more than a century old – including in Boston, the closest big city that his team studied until Thursday's explosions.

Although natural gas leaks occur quite frequently, serious consequences are not. From 1998 to 2017, an average of 15 people per year of incidents related to gas distribution in the US "Significant incidents" – doing things that result in injury or death result in at least $ 50,000 damage or lead to a fire or explosion – happen about 286 times a year.

That may sound like a lot. But yes, the streets of Boston have an average of four gas leaks per mile.

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Rachel Gutman is assistant editor The Atlantic Ocean.