At least 100 students were evacuated from The Union around 4:15 p.m. Tuesday.

The exact cause is still unknown, but Union Director Jennifer Novotny said six to 10 buildings lost power, and The Union was out the longest.

David Law, project manager engineer with Facilities and Services, said “it’s construction-related,” but the workers didn’t do anything that caused the outage. He said it probably happened when university workers were switching the wires.

In the past Novotny said construction caused power outages were a somewhat regular occurrence.

“I’m guessing this will probably not be the first of its kind,” she said. “It’s probably going to happen again, but we’ll try to keep it to a minimum.”

Along with losing power, two of the buildings — The Union and Larson Commons — had to evacuate due to a fire alarm.

In The Union, smoke was detected in Weary Wil’s Sports Grill, said Keith Skogstad, assistant director of The Union. When the power went out, the exhaust fan stopped working, and there was still smoke and steam in the air.

“With nothing pulling it out, the room filled up with smoke,” Skogstad said. He said Larson’s situation was probably similar.

Novotny said a difficult aspect of the process was evacuating students from The Union.

“You have to evacuate,” Novotny said. “It’s not optional.”

Everyone was let back into The Union at around 4:26 p.m.