Methane leaks explain exploding man-holes

Researchers have found that natural gas is leaking all over the city of Washington, D.C. Methane concentrations were mapped all over the city, finding concentrations up to 50-times more than the average background levels of cities.

The majority of natural gas used throughout the US is methane. Although when people think of the phrase 'greenhouse gases' they usually link it to carbon dioxide emissions. However methane is a more influential gas when it comes to climate change as it is 21-times more effective at trapping heat in the atmosphere. The amount of methane in the atmosphere has been rising exponentially, increasing the rate at which climate change is occurring - today there are 1800-parts-per-billion of methane in the atmosphere in contrast to the 650-parts-per-billion 100 years ago.

Methane leakage occurs in a number of ways. Not all of them are due to man-made exploits such as oil and gas production and landfills - swamps and rice paddies also largely contribute to the methane being released into the atmosphere.

In Washington it has been suggested that the cause of the numerous methane leakages might be the city's ageing infrastructure - in particular older pipes beneath the city. This theory was tested by chemical engineer Robert Jackson of Duke University, who - along with his research team - sampled the air of every street in the District of Columbia over a two-month period. Some areas had readings as high as 100-parts-per-million (ppm), well over the average 2-ppm that is typical in cities.

Carbon isotope analysis showed that - contrary to popular opinion about methane leaks being due to the fact that the city is built on a swamp - the methane is coming from fossil fuels. On average fossil fuels contain more of the carbon isotope, carbon-13 - instead of the carbon-12 isotope produced by bacteria found in swamps -  which is the isotope reported in the samples of air taken.

The methane leaks reported by the research have the capability to produce ground-level ozone, which - while not a direct health risk to everyone - can be dangerous for people with respiratory problems as it irritates the lungs.

The most disturbing issue brought to light, in terms of these leaks, is the level of methane found in the city's manholes. Levels as high as 100,000-ppm were found in many of the manholes. It is typically considered that manholes containing 40,000-ppm are on the verge of risk for explosion. This puts a cause to the average 38 'manhole incidents' reported every year in the city.