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May 16, 2011 / Dave Gorham

Anatomy of a Tornado—Why So Destructive?

My thoughts are still with those who lost love ones and their homes in the tornado outbreak a few weeks ago across the South. As most of us along the coast are gearing up for Hurricane Season to officially begin on June 1st, all of us need to remember that severe weather can occur anywhere and any time of year. All of us need to have a plan in place when a tornado warning is issued, although it’s not like you can plan in advance if and when a tornado will strike your particular area. It’s hard to believe sometimes that in just four seconds a tornado can destroy homes that took months to build and which hold a lifetime of memories.

Tornado ripping through Tuscaloosa, AL in April. Photo: WBMA

Damage in Tuscaloosa from tornado outbreak. Photo: Reuters

The deadly tornado outbreak across the South at the end of April took at least 340 lives with the most fatalities in Alabama. Two of the 225 confirmed tornadoes were classified as EF-5, which is the strongest category on the Enhanced Fujita Scale. Winds in these monstrous storms are over 200 miles per hour. According to experts from the Institute for Business and Home Safety (IBHS), EF-2 and EF-3 tornadoes, which are in the 111-165 mile-per-hour range, can destroy single-family homes. A foundation can be wiped clean in a matter of seconds–literally just 4 seconds!

Image: Digital Library of Georgia

No two tornadoes (or homes for that matter) are exactly alike, so the amount of damage depends on how fast the winds are within the tornado, its size, its path and how fast it’s moving.

As a tornado approaches a home, flying debris can shatter windows and damage the exterior walls. In the first second, winds associated with the tornado blowing over your roof can tear away shingles and pieces of your roof decking.

In just two seconds, air will rush in through shattered windows and the pressure will begin to build within your home. The internal pressure will push up against your ceiling and since you already have external uplift on the roof, there will be an enormous amount of pressure on the roof which can cause it to blow off.

Once the roof is gone, the exterior walls are next and those can be wiped out fairly easily just three seconds in. The side walls parallel to the straight-line winds are the ones to go first because they feel the most suction. The front, windward or upwind wall will get pushed in next followed by the back wall within a second.

The interior walls are the next to get pounded by the tornado within four seconds of the initial hit. Interior rooms, such as bathrooms and closets, are probably the safest place to be during a tornado if you don’t have a basement or shelter as these inner rooms typically give you a little more protection since flying debris has to go through a few layers to get there. However, once the exterior walls or roof is gone, the inner walls can go easily because they lack the support they once had. This is why it’s best to find shelter in an interior wall, on the bottom floor away from windows. Also, hiding under a sturdy object, such as a stairwell or table is a good idea. All of this can happen in just a matter of seconds, so seeking shelter immediately is vitally important because you don’t have a single second to spare.

Check out a few safety tips from FEMA about what you need to do before, during and after a tornado.

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