According to IndyStar News:

A utility consultant warned three years ago that manhole explosions would continue to rock Downtown Indianapolis three to five times a year and that Indianapolis Power & Light Co. should install newly designed manhole covers to prevent injuries.

However, IPL has installed only 357 “lift-locking” manhole covers so far, out of more than 1,000 manholes Downtown. It could take another six to 12 years to replace all of the manhole covers, unless IPL steps up the pace.

IPL said the explosions Thursday a few blocks north of the Statehouse were caused by a short circuit and electrical arcing, not aging infrastructure.

IPL officials tried to tamp down concerns that another explosion could happen, including during the Final Four tournament, which will takes place April 4 and 6 at Lucas Oil Stadium. But they acknowledged they couldn’t rule out another explosion.

“I can’t guarantee it, because the fact is, again, the laws of physics will prevail,” Bentley said. He pointed out that electric currents that are released due to a malfunction will always try to find their way back to the ground, sometimes causing explosions or fires.