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How Can Cities Protect Themselves against Gas Explosions?

Leaks are surprisingly common in aging urban underground pipe networks


Aerial view of New York City's East Harlem apartment gas explosion, March 12, 2014.
Courtesy of Adnan Islam, via Wikimedia Commons.

The gas explosion that rocked a New York City neighborhood last month is the latest warning that leaky urban pipelines are badly in need of an overhaul. The National Transportation and Safety Board’s (NTSB) investigation of the East Harlem blast and fire found small gas leaks below the pavement at the site of the March 12 detonation (pdf) that destroyed two buildings, killing eight people and injuring dozens.
 
Investigators have sent faulty sections of 127-year-old cast-iron pipe as well as a section of 20-centimeter (eight-inch) plastic pipe installed in 2011 to the NTSB lab in Washington, D.C., for further testing. There they will try to determine the roles played in the tragedy by iron alloy degradation, pipeline age and joint design connecting the different pipes.
 
Leaks and explosions involving natural gas transmission and distribution pipelines in the U.S. cause an average of 17 fatalities, 68 injuries and $133 million in property damage annually, according to a study released earlier this year. In the January issue of Environmental Science & Technology the researchers described their efforts mapping nearly 5,900 natural gas leaks of varying severity across 1,500 road miles of Washington, D.C. To learn more about the state of the gas pipelines running through several major U.S. cities—in particular those serving New York City—Scientific American interviewed Robert Jackson, professor of environmental sciences at Stanford and Duke universities and the study’s lead author.
 
[An edited transcript of the interview follows.]
 
When did U.S. cities begin installing natural gas pipelines, and why?
Cities first began installing pipelines to carry gas to streetlights almost 200 years ago. The big era of pipeline construction began a little later, starting after the Civil War and ramping up in the first half of the 20th century.
 
What is the source of New York City’s natural gas?
New York gets its natural gas from pipelines as far as Texas and Louisiana. The new pipeline built by Texas-based Spectra Energy and opened on [November 1, 2013], runs under the Hudson River from New Jersey to Greenwich Village. It brings gas from the Marcellus Shale and other areas to the city.
 
Given the size and age of the infrastructure and the number of people served, how would you characterize NYC’s safety record with regard to gas leaks?
The good news is that pipeline safety in the U.S. is better today than it was 20 years ago, a credit to companies doing their jobs. The bad news is that pipeline leaks and incidents still kill a dozen or more people a year and cost consumers $2 billion yearly from leaky pipes. New York City has more leaks per mile than average, but it has older pipes than average.
 
What materials were the original pipes made from, and why were those materials used?
Until about 1950 most of the natural gas pipelines in New York and elsewhere were made of molded cast-iron. It was state-of-the-art at the time.
 
Does the gas itself wear out or damage the pipes or is that primarily the result of cold, wet conditions (plus salt from snowstorms) underground?
Corrosion inside the pipes from water and other impurities is a bigger problem upstream near well pads than downstream near consumers. The Pipeline and Hazardous Materials Safety Administration (PHMSA) estimates that about one in seven pipeline incidents nationally is caused by internal corrosion. In a city like New York external factors including frost heaving, cracking, corrosion from water and salt, and leaking pipe joints are a bigger issue.
 
What materials are used to make modern gas pipes, and why is this material used?
Most new gas pipelines today are plastic. Protected steel pipes are often used for higher pressure, longer distance transmission lines. Plastic and protected steel both corrode more slowly than cast-iron and are less brittle.
 
What is the biggest challenge to NYC upgrading its existing gas pipe infrastructure?
Like the old adage about real estate and location, it’s money, money, money. A mile of new pipe in a city like New York can cost a million dollars—the reason companies try to repair pipes first. Sometimes they can also “sleeve” a pipe, inserting a new smaller plastic line inside an old pipe so they don’t have to dig it up. That’s much cheaper.
 
What is the most effective way to cut down on natural gas leaks in NYC and other large cities?
Repair and replace the unprotected steel and cast-iron pipes, some of which are more than a century old. They corrode, crack and, once in a while, leak like a sieve. State public utilities commissions are important levers because they cap the amount of money companies can recover for repairs. There are federal agencies relevant to the discussion, though. FERC [the Federal Energy Regulatory Commission] regulates interstate transmission of natural gas—plus oil and electricity—from the standpoint of commerce. PHMSA, a part of the Department of Transportation, regulates pipeline safety. The distribution companies, of course, are responsible for actual pipeline safety operations.
 
New York State’s Public Service Commission has ordered New York City’s utility Con Edison to replace 70 miles of pipe per year by 2016. Could you put this number in perspective?
Recently I did an analysis looking at pipeline replacement rates for different cities between 2004 and 2013. Between 2004 and 2012 Con Ed replaced about 15 miles of cast-iron pipes a year—not much compared to the 1,400 miles they had at the start. Between 2012 and 2013 they replaced 110 miles, substantially more. In total, Con Ed was on track to replace its cast-iron pipes in about 40 years. Duke Energy of Ohio, which serves Cincinnati, had the best track record in the country, replacing 80 percent of its cast-iron pipes through an aggressive program approved by the Public Utility Commission of Ohio in 2001. In contrast, Baltimore Gas and Electric was on track to replace its cast-iron pipes in 140 years, by around the year 2150. They need less tortoise and more hare.
 
What, if anything, makes NYC’s natural gas pipe system significantly different from systems in other large U.S. cities?
New York’s pipeline network is pretty similar to networks in other older cities such as Boston and Washington, D.C. In both of those cities our team has mapped thousands of natural gas leaks block by block.
 
When did utility companies begin using the compound mercaptan to add odor to their gas networks as a safety measure?
A natural gas explosion in 1937 killed 300 students and teachers at an elementary school in New London, Texas. This tragedy prompted companies to start adding an “odorant” into natural gas, which is odorless.
 
Are there any good alternatives to natural gas use in a city?
There are bad alternatives to natural gas use in the city. Burning low-grade heating oil is probably the worst, giving off more soot than all the cars and trucks there combined. It’s one of the reasons there are 300,000 kids with asthma in New York City. For power plants, burning natural gas is cleaner than coal and dirtier than wind, solar and hydropower.

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