Washington, Jan 17 (IANS): After Boston, researchers have now detected thousands of potentially harmful natural gas leaks in Washington, DC.

The aging cast iron pipes beneath the streets of the US capital are causing the leaks that pose explosion risks, health concerns, impact on the economy and contribute to climate change, warned a paper published in the journal Environmental Science and Technology.

The team of researchers, led by Robert Jackson, drove all of the 1,500 miles of roads in Washington, DC with an instrument that took methane readings close to the ground every 1.1 seconds.

During the survey, the scientists found nearly 6,000 leaks - with the highest concentration of methane at about 45 times what would be expected with no leak.

Methane, a far more potent greenhouse gas than carbon dioxide, is the primary component of natural gas.

It can react with nitrogen oxides and spur the formation of ozone, which can aggravate asthma and other lung conditions.

At 19 sites with high concentrations of methane, the researchers tested the manholes and found that some of them had alarmingly high concentration of methane that could cause explosion.

At 5 lakh parts per million, such high concentration of methane is about 10 times greater than the threshold at which explosions can occur.

However, even after notifying the gas companies, the researchers in a follow-up test found that nine manholes still had dangerously high levels of methane.

On average, natural gas pipeline accidents kill 17 people a year in the US.

Leakage of potent greenhouse gas in such large scales not only contributes to climate change at global level, it can also affect the local economy.

Property damage is estimated at $133 million annually, and by one estimate, gas customers in the US between 2000 and 2011 absorbed the cost of escaping gas to the tune of $20 billion.

"Replacing old cast-iron pipes would improve consumer safety and air quality, save money, and lower greenhouse gas emissions," the researchers added.

In a previous study conducted in Boston, the team mapped out about 3,400 pipeline leaks along the city's 758 miles of roads.