Shattered glass littered the lobby of the building, and there was significant damage to the first floor, according to LAFD Batt. Chief Fred Mathis.
The building has been yellow tagged, which means there's limited entry into building.
Employees of an embryo clinic on the twelfth floor gathered outside, concerned that their cultures may not survive without power.
"That's really the most important thing up there," said Dr. Briana Rudick of USC Fertility.
The backup power system kicked in, saving the cultures, but dozens of patients will have to find another way to get time-sensitive treatments.
"We're basically trying to figure out everybody who was supposed to come in today. We are calling them, letting them know that they can't come in, and then anything that needs to be done, we're trying to figure out whether there's another office that they could go to just for the day, or whether there's another lab that they could go to get their blood drawn," Rudick said.
"There's no air conditioning, there's no power, so most of the people are going home,"said Rene Lopez, chief building engineer.
Officials said the cause of the explosion is still under investigation, but they believe an electrical malfunction inside a Los Angeles Department of Water and Power underground vault may be to blame.
No injuries were reported. More than 80 firefighters responded to the incident.
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