{"id":16044,"date":"2013-08-29T10:33:49","date_gmt":"2013-08-29T15:33:49","guid":{"rendered":"http:\/\/stateimpact.npr.org\/oklahoma\/?p=16044"},"modified":"2013-09-05T10:53:01","modified_gmt":"2013-09-05T15:53:01","slug":"twister-truths-can-nothing-survive-an-ef5-tornado","status":"publish","type":"post","link":"https:\/\/stateimpact.npr.org\/oklahoma\/2013\/08\/29\/twister-truths-can-nothing-survive-an-ef5-tornado\/","title":{"rendered":"Twister Truths: Can Nothing Survive an EF5 Tornado?"},"content":{"rendered":"
\"The<\/a><\/p>\n

Joe Wertz \/ StateImpact Oklahoma<\/p>\n

The skeleton of a home on Lakeview Drive in Moore, which was ravaged by the May 20, 2013 tornado.<\/p>\n<\/div>\n

This is part two in our Twister Truths series where we use data to kick the tires on the conventional wisdom underlying severe weather policy in Oklahoma. Read part one here<\/a>.\u00a0<\/em><\/p>\n

Despite the risk that comes with living in Tornado Alley, many Oklahomans are reluctant to build tornado shelters. And state and local building codes don\u2019t factor for twisters.<\/p>\n

One reason, researchers say, is a public perception that \u201cnothing can survive an EF5 tornado.\u201d Indeed, it\u2019s hard to imagine any structure outlasting the violent winds and the devastating cloud of shrapnel that accompanies an EF5.<\/p>\n

Comments like this one<\/a>, spotted on a tornado-related story on Gawker\u2019s science blog io9, summarize a common perspective:<\/p>\n

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\u201cWith an F5 tornado you get the ‘house swept away – only foundation is left’ situation – and the only *safe* place from an F5 is underground or out of it’s path. These tornadoes are the ones that literally have pealed up the road where it passed.\u201d<\/p>\n

This notion that the worst tornadoes obliterate everything in their path has even factored in some Oklahomans\u2019 deadly decisions to get in their cars and try to outmaneuver storms. In one particularly harrowing story<\/a>, a mother and her 17-day-old baby were sucked out of their family minivan in the EF5 tornado that carved through the Oklahoma City area on May 31.<\/p>\n<\/blockquote>\n

But is it true: Can nothing survive an EF5?<\/p>\n

Understanding the Scale<\/h3>\n
\"A<\/a><\/p>\n

Gene Blevins \/ Reuters\/Landov<\/p>\n

A massive storm front in May 2013 spawned a swarm of tornadoes, including this one near the Kansas\/Oklahoma border.<\/p>\n<\/div>

The question of survivability has two components: People, and the structures they inhabit when severe weather strikes.<\/p>\n

But before we tackle that question, it\u2019s important to understand what, exactly, an EF5 tornado is, and how the most severe twisters are categorized.<\/p>\n

Directly measuring a tornado\u2019s wind speed is difficult because the storms tend to destroy instruments. So meteorologists have to estimate tornado wind speeds. The original \u201cFujita Scale\u201d that ranked these estimates was used from 1971 to 2007, but the estimates weren\u2019t really based on actual, measured tornado wind speeds.<\/p>\n

So researchers adopted the classification system used today, the \u201cEnhanced Fujita Scale.\u201d<\/a>\u00a0That scale, which goes from EF0 to EF5, still uses wind speed estimates, but ones that are based on more-accurate surveys of various tornado-damaged buildings and structures. An EF5 tornado includes gusts of winds of over 200 mph, based on these updated damage assessments.<\/p>\n

When an EF5 tornado touches down in habited areas, you can surely expect massive amounts of damage. But just because a tornado meets a meteorological definition of an EF5 storm, it doesn\u2019t necessarily mean you or your house will experience those conditions.<\/p>\n

And despite the horrific scenes of tornado destruction that have become all too familiar in Oklahoma, EF5 tornadoes are survivable \u2014 both for people and structures. And that has important public policy implications.<\/p>\n

Structures & Building Codes<\/h3>\n
\"Tim<\/a><\/p>\n

Joe Wertz \/ StateImpact Oklahoma<\/p>\n

Tim Marshall, a meteorologist and civil engineer, points at the foundation of a home destroyed in the May 20 tornado in Moore. The home's walls were ripped from the foundation because nails were used instead of bolts. <\/p>\n<\/div>\n

The \u201cnothing can survive an EF5\u201d myth is a detriment to policies concerning home and commercial building construction, says Timothy Marshall, a meteorologist and a civil engineer at Haag Engineering in Dallas.<\/p>\n

\u201cThe logic goes: If nothing can survive, why do anything?” Marshall told StateImpact in a July interview.<\/p>\n

Just because a tornado is given an EF5 designation doesn\u2019t mean that every structure in its path actually experiences the full brunt of it. In fact, recent research suggests that most structures don\u2019t.<\/p>\n

One such study<\/a> was by Kai Pan, Peter Montpelier and Masoud Zadeh, who analyzed destruction from the May 3, 1999, F5 tornado in Moore. One thing they found was a \u201cdamage gradient\u201d that was most severe in the center of the tornado path and less severe near the edge. That\u2019s not surprising, but it\u2019s worth remembering that when we talk about tornado damage: it\u2019s not all or nothing.<\/p>\n

\"Stella<\/a><\/p>\n

Joe Wertz \/ StateImpact Oklahoma<\/p>\n

Stella and Jack Howard (left and right) with their daughter, Dawnelaina (center), sit with the remains of their Moore home. The Howards built this house after their last one was destroyed by the May 3, 1999, twister.<\/p>\n<\/div>\n

Even homes across the street from each other experienced the effects of the same winds differently, depending on quirks such as whether their garage doors faced the wind or not.<\/p>\n

Marshall has studied how buildings withstood the F5 twister that tore through Moore on May 3, 1999 as well as the EF5 on May 20, 2013. What he says seems surprising: Most of the destruction in an EF5 doesn\u2019t come from 200 mph winds, it comes from much weaker winds.<\/p>\n

Other research of tornadoes in other states back up Marshall\u2019s observations.<\/p>\n

The tornado that killed 162 people and damaged more than 8,000 buildings in Joplin, Mo. in May 2011 provides another example of how, even in the most severe storms, most damage is done by comparatively weak winds.<\/p>\n

While Joplin\u2019s tornado was classified as an EF5, no EF5-level damage was found<\/a> on any of the buildings, according to a study by the American Society of Civil Engineers<\/a>. Of the 5,000 buildings that were destroyed, most of the damage was done by winds of EF-2 level winds of 135 mph or less, the engineers found.<\/p>\n

From The<\/em> Joplin Globe<\/em>\u2019s Wally Kennedy<\/a>:<\/p>\n

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Had the houses in the tornado zone been built with hurricane ties \u2014 metal clips that fasten the rafters and trusses to the exterior walls of a house \u2014 the damage would have been much less. It is one of the recommendations coming out of their analysis.<\/p>\n

\u201cThe study team believes that a relatively large number of buildings could have survived in Joplin if they had been built to withstand hurricane winds,\u201d said Bill Coulbourne, a member of the ASCE engineering team that came to Joplin.<\/p>\n<\/blockquote>\n

Damage from winds of 135 mph and less is largely preventable. And Marshall says the necessary upgrades are pretty cheap. \u201cBolts and clips and straps in the proper place\u2026 $500-$1,000 on a house, that\u2019s all,\u201d he says.<\/p>\n

After surveying the damage in Moore in 1999, Marshall says he told city officials they should upgrade the residential building code to require stronger foundations, hurricane clips and other metal brackets and ties to strengthen walls and roofs.<\/p>\n

No changes were made, but city and state officials tell StateImpact stronger construction standards are likely to be enacted after the May 2013 tornadoes in Moore and Oklahoma City.<\/p>\n

People & Storm Shelters<\/h3>

The EF5 question isn\u2019t just about building codes. It also relates to tornado shelters. As the Gawker commenter above illustrates, many people believe that the destructive power of an EF5 makes an underground shelter the only safe place to go.<\/p>\n

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