wrote in message

stuff snipped

The biggest problem with the suction/pressure issue is when the
building envelope is penetrated. That is what the impact rated windows
or shutters are all about. Once high pressure air enters and you have
the lower pressures on the roof or other side, forces are increased.
Once the destruction gets started, it proceeds pretty fast throughout
the structure. The more you lose, the more you lose.

I read in several places that the pressure differential theories about
tornadoes and open windows are mostly myth and that the impact-rated glass
is mostly to prevent flying glass shard and other debris-related injuries.

http://www.spc.noaa.gov/faq/tornado/safety.html says:

Flying debris is the greatest danger in tornadoes; so store protective
coverings (e.g., mattress, sleeping bags, thick blankets, etc) in or next to
your shelter space, ready to use on a few seconds' notice . . . Forget
about the old notion of opening windows to equalize pressure; the tornado
will blast open the windows for you!

http://www.accuweather.com/en/weathe...-debunke/61918

says: Similarly, Americans have held on to various other myths causing
them to act dangerously and incorrectly in the face of a volatile tornado.
1. Opening windows during a tornado will relieve pressure and save a house
from destruction

Opening windows during a tornado provides no benefits. Though tornadoes are
caused by intense pressure, merely opening windows will not alleviate or
equalize this. Because of the intense power of a tornado, it is best to seek
shelter underground in a basement, or in a room with no windows altogether.
Opening them only creates a portal through which more debris can enter your
home.

So I am not sure what bottom line is about internal and external air
pressure. It does seem that impact rated windows are very useful in keeping
flying debris OUT of a house. The great tidal wave that struck Bander Aceh
a while back spared some buildings that had open first floors (allowing
debris to pass under the main structure). It also spared some buildings
that were parallel to the flow of the debris-laden water. The latter
presented a much smaller target for water-borne debris than buildings that
got hit broadside with the tidal wave.

--
Bobby G.