A warning siren at a nuclear power plant accidentally went off early Sunday morning, scaring hundreds of residents who flooded the sheriff's substation switchboard with calls.
"We had about 400 calls in about an hour," said Sheriff's Sgt. Paul Falk. "The dispatchers were definitely busy."
The air-raid-type siren, one of 52 located within 12 miles of the San Onofre Nuclear Generating Station, sounded at 1:12 a.m.
It blared for more than four minutes before it was shut off by a Southern California Edison employee who happens to live nearby, said Edison spokesman David Barron.
"It was either a problem with the electrical equipment that supports the siren or the communication line that goes to the siren," Barron said. "We don't believe the box was tampered with, because it's located in a communications tower at the top of the hill and it's surrounded by a tall fence."
Barron said that although they are maintained and inspected every year, the outdoor sirens can be affected by weather.
The plant was operating normally Sunday. Company technicians were investigating the mechanical malfunction that set off the oval-shaped siren on a hill on Avenido Pico, at the Salvador Peak Communications Site.
There are 17 other sirens in San Clemente. More sirens are in San Juan Capistrano, Dana Point and Camp Pendleton and on state beaches near the plant.
Barron said the plant sends out informational brochures every other year to San Clemente officials and to new residents explaining that they should tune in to local television and radio stations to hear about emergencies and receive instructions.
However, Barron acknowledged it took almost an hour for local news sources to announce the false alarm.
"I don't think people understand that they should turn to the TV or radio. They tied up all of our 911 lines for 20 minutes," said dispatcher Kathy Johnson. "If anyone had an emergency, they couldn't get through.
Associated Press contributed to this report.