Hundreds of revelers scrambled for safety after the blasts sent fireballs shooting into the sky Saturday night at Old World Village, a German-themed dining and shopping complex on Center Avenue.
"All of a sudden, this giant explosion happened at the entrance. We were walking towards it, and then we could feel the heat of the flame like on our foreheads," witness Nicole Hallas said. "At that point, we saw everyone running and exiting the whole event."
Owner Bernie Bischoff called firefighters and cleared the dining area after noticing an odd odor coming from the electrical vault, Old World spokesman Dan Escamilla says.
A transformer exploded while a restaurant employee was leading fire crews to the underground vault, which had a 50-lbs. metal lid that flew off during the first blast around 8:30 p.m. The restaurant worker suffered burns to more than 38% of his body and was listed in moderate to critical condition Sunday.
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Two firefighters were injured while investigating the initial explosion. Witnesses say the lights started to flicker and the power went out before the explosions only about a minute apart rocked the restaurant.
"It's not abnormal that in an underground vault, when there's one explosion, it can be followed by others. In this case, there was. So perhaps there were three," said Jeff Lopez with the Huntington Beach Police Department.
Bischoff was severely injured in the explosions, which knocked out power for about 300 customers overnight Saturday.
"We've just had all these family traumas happen, and this is just one other added thing to our family that could have been avoided, and here we are," Bischoff's sister, Cyndie Kasko, said. "Now he's gonna have to suffer. He's got burns on both his arms, his head, both his legs."
Kasko wrote in a post on the restaurant's Facebook page that Bischoff is a "hero" who is "fighting for his life." She added that the restaurant planned to reopen Monday and resume Oktoberfest events on Wednesday in celebration of "the survivors of this tragic event."
A third civilian, who has not been identified, also sustained injuries.
The building was not significantly damaged, officials said.
Kasko said Southern California Edison crews were assisted by former and current restaurant employees who came "together as a family to help clean up this big mess."
The cause of the explosion remains under investigation.