Tornadoes and open windows?

[pilot141]

As I sat here in Del Rio, TX last night and listened to the storm warning sirens, I glanced at my (unopenable) hotel room window.

I thought back to when I was growing up, and I remember being told that when a tornado was coming to open up all the windows in the house so that the pressure could equalize if the tornado came close by, thus saving your windows from blowing out.

I then seem to remember hearing (much more recently) that this was nonsense - something about if the tornado got close enough to create that much low pressure the wind was pretty much going to tear your house apart anyway.

So which is correct?

[Mr.Blue_Sky]

What you heard recently. Opening your windows a few inches or a few feet will not stop a 200mph+ storm from ripping your house apart.

[David_Simmons]

*Originally posted by pilot141 *
**As I sat here in Del Rio, TX last night and listened to the storm warning sirens, I glanced at my (unopenable) hotel room window.

I thought back to when I was growing up, and I remember being told that when a tornado was coming to open up all the windows in the house so that the pressure could equalize if the tornado came close by, thus saving your windows from blowing out.

I then seem to remember hearing (much more recently) that this was nonsense - something about if the tornado got close enough to create that much low pressure the wind was pretty much going to tear your house apart anyway.

So which is correct? **

Don’t waste time opening windows. Head for the storm cellar. The force exerted on walls by differential pressure is huge and the viscosity of the air prevents its rapid escape so that differential will exist.

After all, a difference in pressure in the vicinity of 1/2 psi between the top and bottom of the wings will lift a 747 right off the ground.

[kniz]

Back in 1974 a tornado came thru Cincinnati and tore up things, lifted up and came back down on Xenia, OH. It tore the whole town up. There was a famous picture of a subdivision in Xenia, where everything in sight was flattened except one house. It may not have been in the greatest condition, but it was still standing and the roof was still on it. Word got out that the owner was from Oklahoma and that he happened to be home and knew to run around opening all the windows.

That was when I first heard this particular claim, but soon afterwards a disclaimer came out saying that opening windows would not save a house.

[Una_Persson]

I think I’ve seen that same picture, kniz, except used in a claim that “steel frame houses will withstand even a tornado!”

Not that they aren’t cool and all, but…

[Threadkiller]

From Hurricane Watch: Forecasting the Deadliest Storms on Earth p. 186.

Years ago, engineers and meteorologists believed that the higher pressure inside a building caused it to “explode” when low pressure, such as in a hurricane or tornado, passed over the building, and that the pressure inside couldn’t equalize quickly enough with the lower outside pressure. Close study of damage and wind tunnel tests with models of different kinds of buildings have shown this is not what happens. Instead, wind flowing over a roof or around the corner of a building creates a low pressure area on the lee side of the flow, perhaps “sucking” off the wall on that lee side or even lifting off the entire roof. Once a roof is lifted off, the wind might blow a wall or walls outward, giving the impression that the building has exploded. Meteorologists and emergency managers now teach homeowners to ignore the old adage about opening windows to “equalize the pressure.” It’s not only a waste of time; it’s counterproductive, since open windows allow the wind in.