MINNEAPOLIS (WCCO) — During Severe Weather Awareness Week, Minnesota counties and cities tested all of their tornado sirens. But who decides when the sirens should be sounded? And who pushes the button?

“The tornado alert sirens come out of the Hennepin County Sheriff’s Office,” said Hennepin County Sheriff Rich Stanek.

In Hennepin County there are 242 sirens, all controlled through the central communications center. According to Stanek, that’s the standard set up.

Cities own and maintain their sirens, and they’re all linked together and operated out of county 911 dispatch centers.

“Once we’re notified, the bad weather is verified, the alarms are sounded,” said Stanek.

The 911 centers are obvious hubs, because someone is always on duty. The Hennepin County control is 1970s radio frequency technology, but deputies say it’s extremely reliable.

They have the power to control just one individual siren, or sound the sirens in one city, but typically they operate the sirens by zones. Hennepin has four zones, so they don’t warn Edina when a storm is bearing down on Rogers.

A siren can sound for many reasons.

“It doesn’t always have to mean tornado, most often it does,” said Julie Anderson, a spokesperson for Minnesota’s Homeland Security and Emergency Management Agency.

The state manages the sirens within 10 miles of Minnesota’s two nuclear plants. But a siren could sound for reasons other than nuclear problems.

“It could be any kind of hazmat situation, any kind of chemical spill. Anything that is life safety,” said Anderson.

They also could be sounded for an attack. There’s actually a separate button labeled “attack” with a different tone.

Usually the National Weather Service issues a tornado warning. That comes into the 911 center via a ticker printout and a phone call, then the sirens are triggered.

But two years ago when a tornado skipped through south Minneapolis, a firefighter spotted it on the ground and radioed the county, triggering the sirens.

To fire the system, a dispatcher selects the type of alarm, the zone to sound and then pushes two buttons simultaneously to activate the sirens. There is a delay of about five seconds, giving the dispatcher the chance to abort the sirens if there was a mistake.

There’s newer technology that links a tornado’s projected path to the siren system so they’d sound in a more narrow area automatically. Cell phone companies are also working on ways to use their towers to trigger your phone, if you’re near a dangerous storm.


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