INDIANAPOLIS -- Training explosives left behind by the Transportation Safety Administration prompted a portion of Indianapolis International Airport to be evacuated early Wednesday morning, TSA officials said.

Concourse D at the airport was cleared between 5 and 6:30 a.m. when officials discovered the materials. About 500 people were evacuated.

TSA spokeswoman Lara Uselding said airport police determined that the suspect items were "components used by TSA to train its officer workforce" and that passengers were never in danger.

"A TSA training officer had used the components for training purposes overnight and then inadvertently left them at the checkpoint," Uselding said in a statement.

She said TSA staff at the Indianapolis airport were investigating how the items were left behind and reviewing procedures to prevent a repeat.

The materials were found in a tray on a conveyor belt at a Transportation Security Administration checkpoint, said airport police Maj. Tom Hanna.

Passengers were never at risk because the explosives were inactive, he said.

"Due to some of the things that the TSA screener saw and the initial response of what it looked like ... something ratcheted it up, at which time they called the bomb squad," Hanna said.

Airport spokeswoman Patzetta Trice said a vest containing the materials was left at the checkpoint with no owner nearby.

"It was just left sitting and there was no individual associated with it," she said.

Airport security workers frequently find unattended bags, but officials said that what happened Wednesday morning is not routine.

Airport spokeswoman Susan Sullivan said no flights were canceled but the evacuation did cause delays for US Airways and United Airlines. She said both airlines experienced delays on four express regional jets that were bound for the East Coast.

"When I came, they had just opened up the dropoff area," said passenger Teresa O'Mara. "The lines have been crazy."

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