The Southern diners are used for more than a great place to get a late night meal.

Waffle Houses are known as the reliable diner that no matter what, is always open. 24 hours a day and seven days a week, Waffles House diners serve up delicious breakfast favorites like eggs, bacon, sausage and of course, waffles. Whether it's late at night or Christmas Eve, Waffle House diners are always open to feed your appetite. Even during natural disaster. Because of the restaurant chain's reliability to be open, FEMA even uses them to gauge just how bad a natural disaster really is.

The "Waffle House Index" as it's called shows how much an area is affected by a natural disaster and how fast it can rebound after the disaster. In a blog post back in 2011, former administrator Craig Fugate had this to say about why they used Waffle Houses as barometer:

"The Waffle House test just doesn't tell us how quickly a business might rebound — it also tells 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 — signaling a strong recovery for that community."

So how does the Waffle House Index work?

FEMA looks at all the Waffle Houses in a certain region affected by a natural disaster, then gives them a color rating of either green, yellow or red. Green means that the Waffle House is fully operational and open for business. Yellow means that the Waffle House is open, ut running with a limited menu. Red means the Waffle House is closed and it is bad. Like, really bad.

Fugate says he created the system back in 2004 when he was the emergency management director for Florida. There's even a Waffle House News Twitter that is letting people know how Waffle Houses are fairing during Hurricane Harvey before and now Hurricane Irma. About 250 Waffle Houses are expected to be impacted by Irma. As of September 3rd, only one Waffle House remained closed due to Hurricane Harvey.