Predicting Manhole Explosions

Posted by admin updated on 09 Jul, 2010

Every so often in New York City, a disk of cast iron weighing up to 300 pounds will burst out of the street and fly as high as several stories before clattering back. Ever since Thomas Edison fired up the city’s commercial electric grid in 1882, New Yorkers have had to contend with the random hazards of smoking, flaming and exploding manholes. Many of the blasts result from decrepit wiring, which can lead to sparks. Throw in a bit of gas and a confined space and, like a combustion engine, the blast can move metal. Until recently, there was no way of knowing where or when the next outburst would occur; repairs commenced only after a manhole had growled.

But in 2004 Con Edison began a proactive inspection program, with the goal of finding the places in New York’s snaking network of electrical cable where trouble is most likely to strike. The company called upon a team of Columbia University researchers to help predict the likelihood of manhole explosions.

The team tackled Manhattan first, where beneath the borough’s streets and avenues lies 21,000 miles of cable. The scientists weeded out irrelevant information such as parking information for ConEd vehicles. They then ranked the manholes of Manhattan by vulnerability to serious events and developed an algorithm that directs a computer to identify subterranean trouble spots.

Serious manhole events are rare — only a few hundred occur each year even though there are 51,000-odd manhole and service boxes in Manhattan. “Finding a pattern when something is very rare is very hard,” says computer scientist Gary Weiss of Fordham University in the New York City. “If you only have a few examples, there are so many patterns that can fit those few examples… you can’t really tell the difference between a pattern that is meaningful and one that is coincidental.”

The algorithm’s job was to “learn” from the past records and find meaningful patterns. Then it could predict the likelihood that a particular manhole with particular characteristics would have a future flare-up. The team discovered that manholes with larger cables — and so a larger amount of insulation subject to decay and thus to sparking — turned out to be more vulnerable to serious events.

Con Edison blind-tested the team’s model by withholding information on a recent set of fires and explosions. The top 2% of manholes ranked as vulnerable by the algorithm included 11% of the manholes that had recently had a fire or explosion.

Tweaking and adding more data has improved the model further. Con Edison is now using it to help prioritize inspection and repairs on the grid. The team has just completed rankings for manholes in Brooklyn and the Bronx.

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Consolidated Edison, Inc. (NYSE: ED) is one of the largest investor-owned energy companies in the United States, with approximately $14B in annual revenues and $33B in assets. The company provides a wide range of energy-related products and services to its customers through its subsidiaries.