State and county Civil Defense authorities rely on six primary radio stations to broadcast emergency warnings in the event of an impending natural disaster, such as a tsunami generated by a powerful earthquake.

They're part of an emergency alert plan mandated by the Federal Communications Commission that was last revised in Hawai'i in 2003. Each station uses special dedicated equipment that takes a digitally encoded radio message from a civil defense agency and automatically puts it on the air. Those messages also can be sent by the president, the governor, the National Weather Service and police.

State Civil Defense officials used it Sunday at 9:57 a.m. to tell the public there had been a 6.7-magnitude earthquake but no impending tsunami, and also to urge people to limit driving and telephone and cell phone use.

Most people statewide knew well before that point that there had been an earthquake and some had listened to radio interviews with state officials explaining the situation.

Because it can be heard across most of the state, KSSK-AM is often considered to be the state's primary emergency AM station. But the state designates stations in each county, according to the plan.

"Generally, you go with the stations that have the greatest reach," said state Civil Defense spokesman Ray Lovell.

But Lovell also said that people should simply search across the radio dial in the event of an emergency because, as Sunday's disaster proved, some can be knocked off the air.

'A GRAY AREA'

The Emergency Alert System — often simply called the EAS — is used primarily for evacuations that need to be done immediately, said John Cummings, spokesman for O'ahu Civil Defense.

"Sunday's event was a gray area," he said. "We didn't need to evacuate. There was no tsunami threat. The system is not designed to say there is no tsunami coming."

But after Sunday's events, O'ahu Civil Defense authorities are discussing with their state counterparts on ways to change that, Cummings said. It was already on their agenda because of the massive freeway tie-up last month, he said.

Telling people that there is no danger would put people at ease, he said.

"It would eliminate unnecessary travel from the shoreline and possibly prevent an accident," Cummings said. "There is some merit to do that. And people might be more receptive to other messages about staying off the road if they are not poised on the evacuation mode."

Cummings said O'ahu officials still have the use of the old Emergency Broadcast System, which was largely replaced by the EAS. The older system, which also can be used by state Civil Defense, requires someone at a radio station to manually allow a broadcast by authorities, Cummings said.

While the state used the EAS on Sunday, the county used the EBS on Sunday at 7:57 a.m., relying on a message light that is supposed to alert technicians at radio stations that an alert was coming, Cummings said. Under normal circumstances, a technician would adjust the station controls to put the EBS message on the air.

RADIO SIGNALS

There was no confirmation that anyone put their message on the air and O'ahu Civil Defense officials, working in the basement of the county municipal building, could not monitor their own broadcast because they cannot receive AM and FM radio signals below ground, Cummings said.

"At this time we are unaware if anyone was able to receive the message and broadcast it," he said. "It would go out to all stations."

But Cummings said he wouldn't be surprised if radio technicians working that morning were too harried to see the blinking light on their control boards.

No one at KSSK-AM and KSSK-FM received that message, said Chuck Cotton, vice president and general manager for Clear Channel Hawaii, which owns the stations.

"When something goes wrong at their end, we get nothing," Cotton said. "They may have sent it but we never got anything."

At that hour, though, Cotton said his staff was scrambling to get accurate information. He said the station's first message, at 7:28 a.m., was a 15-second explanation that there had been an earthquake — with no other details offered. Shortly after 8 a.m., state officials were calling with information.

One of the things absent Sunday — and for good reason, state Civil Defense spokesman Lovell said — was the state's most visible warning mechanism: Its network of sirens.

They are only used when the public needs to know about an immediate threat to safety, which wasn't the case after this disaster, he said.

The sirens are tested monthly at 11:45 a.m. on the first working day. They scream for 45 seconds on every island, triggered simultaneously by county Civil Defense authorities.

"We use the sirens to get people's attention," he said.

At their core, the sirens scream one urgent message to the public: Turn on your radio for more information.

Reach Mike Gordon at mgordon@honoluluadvertiser.com.