Still no word what led to a series of explosions downtown Wednesday

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Indianapolis Power and Light said a busy stretch of Meridian Street will be open Thursday, despite a series of explosions Wednesday afternoon.

The utility company says one of their network protectors — basically a large circuit breaker — exploded in an underground vault

IPL crews spent the afternoon underground near 26 South Meridian trying to figure out what caused part of their equipment to fail. Wednesday night, they said they still didn't know what caused the failure that led to underground explosions, leaving people frightened and several offices downtown and parts of Circle Center Mall without power.

IPL says they regularly check their equipment to make sure it's in working order, but there's no word yet on when that network protector was last checked.

PHOTO: IPL crews spent the afternoon underground near 26 South Meridian trying to figure out what caused their equipment to fail

At first, no one knew what was happening Wednesday afternoon around 1:30. All people knew was that they heard what sounded like explosions and then saw smoke filling the street.

"You just didn't know what it was," said downtown employee Christy Vavra. "You could tell it wasn't a plane crash. It wasn't a car. It wasn't anything like that, but honestly, it sounded like a bomb underneath the building."

It wasn't any of those things, though. Instead, IPL said a network protector, basically a large underground circuit breaker, failed.

"It caused a series of large booms and a lot of smoke," said IPL spokesperson Brandi Davis-Handy. "With any system there can be failures. These things happen."

PHOTO: Heavy brown smoke pushed out from an underground grate around 1:30 p.m. in the 100 block of S. Meridian Street Wednesday after a string of small explosions

This isn't the first time, though, there has been some kind of failure with the IPL's system leading to underground explosions, fires and sometimes explosions of manhole covers above ground.

In June 2011, employees at the Indiana Statehouse were evacuated after a bad electrical connection caused an explosion underground there that triggered other explosions under downtown streets. Two months before that in April, a manhole cover exploded in an alley behind Monument Circle. Just minutes prior, a garbage truck was parked on top of that manhole cover. In January of that same year, several explosions along Massachusetts Avenue damaged the historic Athenaeum building.

PHOTO: In April 2011, a manhole cover exploded in an alley behind Monument Circle

No one was injured in any of those incidents, or the one Wednesday.

"We have checks and measures in place, but like any system, you know these things happen and you can't predict these things," said Davis-Handy when asked if the public was safe.

That's exactly why downtown employee Daniel Herndon said he's changing his pace.

"I'm a bold walk-on-top-of-the-grate kind of guy," said Herndon, laughing.

That won't be the case now.

"I'd be lying if I said I wasn't stepping to the side of the grating, just to make sure I wasn't anywhere near the next explosion," said Herndon.

The problem is, no one can say when the next one will be, where it will happen or why. IPL admits it can't predict the malfunctions, but said its underground network is reliable and safe.

IPL does scheduled inspections of its underground network to check for problems that could eventually lead to equipment failure. So far, there has been no word on when the piece of equipment that failed Wednesday was last checked.

Three years ago, the Indiana Utility Regulatory Commission recommended a third party review IPL's maintenance practices after a series of underground failures that led to explosions.