Page 29 - spaces4learning, Spring 2021

TORNADOES, SHELTERS AND TUBES, OH MY!
By Susan Flanagan
TWISTER. FUNNEL. WHIRLWIND. A tornado by any other name is still considered the deadliest and most destructive natural disaster on earth. Occurring on all continents except Antarctica, tornadoes have both terrified and fascinated man- kind for centuries. The U.S. averages almost 1,300 tornadoes per year, more than all other continents combined.
Yet, surprisingly, it wasn’t until 1950 that the U.S. began to document tornadic events. Compared to winter storms, hurri- canes and floods, tornado history is still in its relative infancy. Even with today’s most modern studies, analyses, instruments and technology, tornado behaviors continue to baffle and mysti- fy experts, leading them to ask (and often disagree) on questions such as:
• What conditions cause tornadoes?
• What is truly happening inside a tornado?
• How do we better analyze the results of a tornado’s impact? • How do we protect ourselves when a tornado strikes?
It is this last question that has driven architects, engineers and the construction industry to develop codes and guidelines such as ICC 500 and FEMA P-361. These guidelines, at least in part, will help to ensure the proper construction of tornado shelters in order to save lives, which is the ultimate goal.
Categorizing Tornadoes
To build a better storm shelter, we must try to better under- stand how and what a tornado can destroy. For many years, the lack of recorded historical data or a standard for categorizing tornadoes made it difficult at best to establish what, if anything, could actually provide protection in the event of a twister.
It wasn’t until 1971 that the efforts of engineer and meteo- rologist Dr. Tetsuya Fujita developed a way to categorize torna- does. Through his decades-long research of weather systems and his on-site analysis of the destruction from various tornadoes, Dr. Fujita created the Fujita Scale, or F scale, which assigned tornadoes an intensity factor level from F0 to F5. The torna- do’s intensity could only be determined after the tornado had passed, as levels were based on surveying the damage caused to a limited type of man-made structures and vegetation.
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For 40 years, the Fujita Scale was used to classify a tornado’s
PHOTO CREDIT KINGSHOPART
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