Survey Gives Clearer View of Risky Leaks from Gas Mains

Analyses across metropolitan Boston show need for better detection of natural gas emissions

Precise measurements of leaks from natural gas pipelines across metropolitan Boston have demonstrated that almost a sixth of the leaks qualified as potentially explosive, and that a handful of leaks emitted half of the total gas lost.

The findings by Boston University researchers differ significantly from results gathered by gas companies and other monitoring groups, and highlight the risks that these "fugitive" gas emissions pose both for safety and the environment, says Margaret Hendrick, a PhD candidate in BU's Earth & Environment department.

Hendrick is lead author on a paper published in Environmental Pollution, which emphasizes the need to develop standardized ways to detect leaks and prioritize their repair.

Natural gas is considered a relatively clean fossil fuel, but a substantial amount of the gas is lost in production and distribution.  In addition to the safety risks, methane (the main component of natural gas) is a major contributor to atmospheric warming.

Gas pipelines may date back as early as the mid-nineteenth century in east coast cities such as Boston.  About a third of the installed pipelines use leak-prone materials such as cast iron, wrought iron or unprotected steel.  There are thousands of gas leaks in these cities, but how the sizes of these leaks vary in an urban area "was a big black box until this project," Hendrick says.

She and her colleagues looked at emissions from cast iron pipelines at 100 sites in greater Boston where leaks had been detected in the air along roadways.  The researchers painstakingly analyzed the release of methane inside custom-built chambers created with plastic buckets and the lids from child sandboxes.  "To fully ascertain the safety hazards of leaks really does require us to get out on the ground with instrumentation," Hendrick explains.

This was the first survey that performed detailed measurements of loss from pipelines on this urban scale, says Professor of Earth and Environment Nathan Phillips, Hendrick's advisor and senior author on the paper.

Risk of explosion doesn't necessarily correlate with the amount of methane leaking, because the local environment around the leak also plays a part.  "Even a very small leak can be a great safety concern," says Hendrick, who notes that a 2014 gas explosion in Dorchester injured 12 people. There were 113 gas distribution pipeline incidents, with 18 fatalities, in the United States that year.

The seven "super-emitter" leaks that released half the methane in the study also raise warning signs for climate change.  Methane accounts for about one tenth of U.S. greenhouse gas emissions.  On average over a 20-year period, a methane molecule released into the atmosphere traps about 86 times as much heat as does a carbon dioxide molecule, Phillips points out.

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