Tornadoes, Shelters and Tubes, Oh My!
- By Susan Flanagan
- 05/01/21
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 mankind
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, hurricanes
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 mystify
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?
PHOTO CREDIT DUSTIE
JOPLIN, MO - MAY 22, 2011: The killer EF-5 tornado which caused extensive damage and
160 deaths forever changed the lives of young and old alike who experienced the devastation.
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.
PHOTO CREDIT KINGSHOPART
Categorizing Tornadoes
To build a better storm shelter, we must try to better understand
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 meteorologist
Dr. Tetsuya Fujita developed a way to categorize tornadoes.
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 tornado’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.
For 40 years, the Fujita Scale was used to classify a tornado’s intensity—until two incredibly violent tornadoes caused experts
to reconsider the F Scale’s accuracy. On May 27, 1997, Jarrell, Texas
suffered devastating destruction when a tornado three-quarters
of a mile long ripped through the town, killing 27 people.
Its slow movement on the ground coupled with estimated wind
speeds over 200 mph caused the tornado to spin almost in place
in certain areas for as long as three minutes, ripping apart everything
it touched and leaving only small remnants behind. Then,
on May 3, 1999, deadly storms yielded what was later determined
to be an EF5, this time striking Moore, Okla. Carving a path
some 37 miles long and with wind speeds estimated to have exceeded
300 mph, the storm killed 36 people and injured another
583, making it the deadliest strike since 1979.
The amount of damage and destruction from these two tornadoes
made engineers, emergency managers and meteorologists
alike question if the Fujita scale of measurement was an oversimplified approach toward classifying tornadoes. Mostly, the F
scale was a subjective assessment based on the damage to a select
group of buildings. It did not take into account multiple types of
construction or construction materials, nor did it correlate wind
speeds with certain types of damage. Accuracy in determining
the scale of each tornado was almost impossible, as was consistency,
and it was thus determined that a change was needed.
Missile Impact Testing
From 2001 to 2004, a panel of engineering and meteorological experts conducted an investigation into the Fujita scale.
Their knowledge and efforts led to the creation of a more robust
and accurate method of determining a tornado’s intensity:
the Enhanced Fujita Scale. Still based upon a damage analysis
methodology, this enhanced version used a combination of
damage indicators (types of structures) and degrees of damage
for each indicator. It also correlated the wind speed with the visually-observed damage. In 2007, the National Weather Service
adopted the Enhanced Fujita scale, and it is still in use today.
Building Storm Shelters
The Enhanced Fujita Scale allowed for more accurate and quantifiable data to be gathered, providing greater knowledge as to
how different materials and structures behave in a tornado. Ultimately,
this information led to the creation of a standard that
would drive better design and construction for safer buildings,
stronger products, testing and verification.
Using the 2000 FEMA P-361 guideline as a legacy document,
in the summer of 2008, the first version of the ICC 500
Standard for the Design and Construction of Storm Shelters was
released. This consensus standard codified the design and construction
of commercial storm shelters for both hurricanes and
tornadoes. It also set a minimum standard of building for these
facilities for governments and various organizations to adopt.
Under the International Building Code (IBC), ICC 500 storm
shelters became required components of certain types of facilities
being built: fire, ambulance, police and 911 call centers,
as well as emergency operations centers—and, most relevantly,
K-12 school facilities with 50 or more occupants.
As knowledge around building safer and stronger storm
shelters expanded, it became apparent that building materials
and components such as doors and windows would need to endure
specific tests to ensure their ability to withstand the winds,
pressures and debris of a tornado. It was also deemed unlikely
that many standard components could pass the difficult tests
needed to become ICC 500-compliant. One of the most challenging of these was the missile-impact test, which replicates
wind-borne debris hitting the component being tested at speeds
of up to 250 mph. Stronger materials and sturdier construction
became needed to pass the testing, often at a higher cost. This
became challenging in that, while these shelters needed to be
designed and constructed to safeguard occupants from a tornado,
one also had to consider that 99.9% of a storm shelter’s life
would be used for another purpose, such as a K–12 gymnasium,
which is often the chosen space to serve as the shelter.
PHOTO CREDIT YELLOW DOG DESIGN WORKS, LLC
FEMA P-361 Safe Room
Storm Shelter Lighting
Daylighting—or illuminating buildings using natural light—is very common in these spaces; however, traditional forms of
daylighting, such as windows, struggled to pass the impact testing.
Skylight manufacturers hadn’t even attempted it. Penetration-protection components like storm doors or shutters could
be added to windows to prevent debris from entering the space.
But they could also inflate the project’s budget and potentially
cause daylighting to be removed from the project altogether.
While eliminating forms of daylighting might have helped reduce
budget, it could come at a greater cost to the students.
Studies by groups like Heschong Mahone and the University
of Oregon have shown that broad-spectrum daylight, when incorporated
into learning spaces, can help to increase test scores
between 20% to 26%; improve cognitive skills, visibility and
mood; and even reduce microbial communities associated with
indoor dust by 50%. With such great benefits, removing daylight
from these spaces was not ideal. So, if windows were too
expensive, what other options did schools have for daylighting?
Before 2018, there really were none, so the storm shelter often
became a windowless space.
Knowing there was a need for an affordable daylighting solution that could endure the stringent testing of ICC 500, Solatube International set out to become the first top lighting manufacturer to achieve ICC 500 storm shelter compliance. Recognized as the inventor and industry leader of the tubular daylighting device (TDDs), Solatube offers a way to deliver daylight into spaces through an advanced optical system. Capturing daylight through a dome on the roof, highly reflective tubing routes daylight downward, eventually delivering broad-spectrum daylight as a consistent source into the facility.
Solatube TDDs already led the industry in certifications having passed demanding product testing such as Federal Blast Testing, Factory Mutual Testing and hurricane coastal requirements in Florida and Texas. With a history of testing and performance success, Solatube felt strongly that its product strengths and manufacturing would be able to succeed in achieving another industry first. In late 2018, Solatube International’s SolaMaster 750DS underwent 3rd party testing for ICC 500 storm shelter compliance, and in early 2019, Solatube International INC became the first top lighting product manufacturer to achieve ICC 500 and FEMA P-361 compliance. Having passed the testing without the need for additional penetration protection, daylighting a shelter no longer had to level a school’s budget, and following the testing and code that so many had worked so hard to put in place meant that occupants could be assured that Solatube’s tubular daylighting device could stand up to the forces of nature.
Conclusion
Tornadoes are violent and deadly events that we’re starting to see
with more frequency and more intensity. The amazing efforts of
people like Dr. Fujita, the members of the forum that developed
the Enhanced Fujita scale, meteorologists, the National Storm
Shelter Association, engineers, scientists and even storm chasers
have helped us better understand how to protect ourselves if we
find ourselves in a tornado’s path. Stronger building codes and
more rigorous testing have led to the construction of safer shelters,
and we owe the people who gave their time to implement
these requirements a great deal of gratitude.
By requiring adherence to the ICC 500 storm shelter code,
governments and organizations can ensure proper testing of
components and compliance with these codes during the construction
of storm shelters. By doing so, they can better prepare
for and protect people from tornadic events. And saving lives is
ultimately the answer.
This article originally appeared in the Spring 2021 issue of Spaces4Learning.