(CBS4) — You know hurricanes are formally ranked from Category 1 to Category 5, based on the severity of the storm. But did you know they’re also ranked by something called the Waffle House Index?

It’s a real thing — and the Federal Emergency Management Agency uses it.

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The comfort-food restaurants are known for staying open 24 hours a day, even under the most severe weather conditions. So when one or more are forced to close, it’s a sign things are getting serious.

The FEMA website describes how the Waffle House Index works: “If a Waffle House store is open and offering a full menu, the index is green. If it is open but serving from a limited menu, it’s yellow. When the location has been forced to close, the index is red. Because Waffle House is well-prepared for disasters… it’s rare for the index to hit red.”

According to FEMA, “major companies such as The Home Depot, Walmart, and Waffle House serve as role models in disaster preparedness… These companies have good risk management plans to ensure that their stores continue to operate when a disaster strikes, and also provide basic supplies to people in their community.”

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Waffle House actually has its own “Storm Center,” which it activated on Tuesday to monitor Hurricane Florence.

According to NPR, the restaurant chain even has “jump teams” it can send into disaster areas to help keep the restaurants up and running. During Hurricane Harvey, Waffle House sent managers from Ohio, Tennessee and Georgia to help out in Houston — “in some cases doing the shifts of storm-stranded local employees.”

The Waffle House Index, also called the Waffle House test, can help officials determine how quickly a community might be able to get up and running again after a disaster.

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“The Waffle House test doesn’t just tell us how quickly a business might rebound – it also tells us how the larger community is faring. The sooner restaurants, grocery and corner stores, or banks can re-open, the sooner local economies will start generating revenue again,” the FEMA website states.