IPL: Cable breakdown may have caused underground blast
A huge underground explosion Downtown in March was probably caused by a breakdown in a 2-year-old cable near the intersection of North Street and Capitol Avenue, according to new testimony filed with the state Monday.
What caused such a new cable to fail remains unclear, although Indianapolis Power & Light Co. pointed out that active steam lines in the vicinity, owned by another utility, Citizens Energy, might have produced "elevated temperatures" underground.
"Prolonged exposure to these elevated temperatures would account for the thermal damage observed on some of IPL's cables removed from this duct line after the March 19, 2015, event and likely contributed to the failure of the secondary cables," according to IPL's testimony.
The cable breakdown generated substantial heat in an underground duct line, which created substantial quantities of combustible gases, some of which flowed into a manhole and started a fire, IPL said in its testimony.
About 1,000 customers in a six-block area lost power for several hours, but no one was hurt in the fire or explosion.
IPL filed more than 100 pages of written testimony, much of it highly technical, with the Indiana Utility Regulatory Commission.
The commission is looking into what caused several explosions Downtown in March, and what the utility is doing to maintain and repair its vast underground network.
The investigation is still in its early stages, and it could take months for regulators to issue findings and possible penalties against IPL.
The company pointed out that it has invested millions of dollars a year in its underground network. The company is now in the process of replacing hundreds of manhole covers with more secure versions. It is also replacing more than 100 480-volt network protectors.
Since 2005, at least 18 fires or explosions in IPL's underground network have rocked Downtown, including 14 in the past five years. Sometimes, flames have shot 25 feet into the air, and manhole covers have been tossed into the sky.
The most recent one was March 19, when a manhole exploded a few blocks north of the Statehouse. It disrupted rush-hour traffic and shut off power to up to six square blocks. Crews rescued one person who was stuck in an elevator because of the blackout.
Less than a week earlier, witnesses reported another blast Downtown, with smoke and fire from a sidewalk grate in the 400 block of Massachusetts Avenue. IPL said some of its underground equipment malfunctioned, but there was no explosion.
The March 19 explosion, occurring just two weeks before the NCAA men's basketball Final Four here, increased pressure on IPL to get to the bottom of the matter.
Within days, state regulators opened an investigation in the matter. Mayor Greg Ballard called the manhole issue "concerning."
IPL had been replacing 50 to 100 manhole covers a year with the safer version, which lifts about 3 inches to allow excess gas to escape when underground pressure builds.
But as of the March explosion, IPL had installed only 357 "lift-locking" manhole covers out of more than 1,000 manholes Downtown. It said it had more than 600 others to replace, then began accelerating the pace of replacements.
At the time, IPL said the explosions were caused by a short circuit and electrical arcing, not aging infrastructure. The company also said weather might have been a factor.
In 2011, O'Neill Management Consulting LLC of Atlanta prepared a 186-page report for the state after a round of explosions, including a massive convulsion that shook the Statehouse.
The consulting firm found that about half of the incidents stemmed from failures in equipment owned either by IPL customers or by another utility. In particular, steam lines operated by Citizens Thermal have become problems at many manhole sites, according to the report, often causing temperatures too hot even to allow IPL to attempt routine inspections.
Call Star reporter John Russell at (317) 444-6283. Follow him on Twitter: @johnrussell99.