That has to change, and building codes and standards need to acknowledge tornadoes and the difference between straight speeds and the variables of wind presented by tornadoes. That is one of the 16 recommendations that resulted from a National Institute of Standards and Technology (NIST) study of the May 2011 tornado that killed 161 and damaged more than 7,500 structures in Joplin, Mo.
The tornado was the deadliest since the first records were kept in 1951, hence the study to determine what factors contributed most to the death and destruction. The NIST team, led by Marc Levitan, looked at four key factors that contributed: storm characteristics; building performance; human behavior; and emergency communication.
For the study, the NIST team looked at the meteorology of the storm, the wind fields and the warning information, including what was provided and how. The team interviewed survivors of the tornado to learn about how they got their information and the actions they took. The team also studied the fatalities, got death certificates, interviewed relatives of the dead and people who were with those who died, and scanned social media to find out as much as it could.
Since most of the 161 deaths occurred inside buildings and were caused by blunt force trauma, building performance and the failings of the buildings to provide life safety were the keys to the study. As with a lot of disasters, there were contributions from multiple factors, but probably the overarching one and most important is the fifth one, which recommends that, “Nationally accepted performance-based standards for tornado-resistant design of buildings and infrastructure be developed and adopted …”
“Building codes for schools and houses and so forth don’t mention tornadoes, so it’s not a surprise that everything fell apart with the wind speeds, particularly in a very strong tornado,” Levitan said. “Wind speeds may be 50-60-70-80 percent greater than the wind speeds in a typical storm in the middle of the country.”
Tornadic winds have significant updrafts, which can increase the uplift on roofs and there will be more debris in the air and more opportunity for window breakage and other damage. “We need to define different levels of building performance like they’ve done with earthquake engineering,” Levitan said. “And then develop the appropriate maps and return periods to go along with those levels of performance.”
That would be a starting point for building owners, architects and engineers working on designing new facilities or retrofitting existing ones. It would mean more than just a “yes, it passed code,” or it didn’t pass, but describe a meaning to it.
Along with the building codes, NIST recommends a new generation of tornado hazard maps to incorporate the latest that’s known about climatology, tornado wind fields and tornado hazard identification.
Once standards and wind speed maps are developed there will be a need for design guides and methodologies; design techniques; construction techniques; and analysis techniques.
“We’re not saying you have to build everything in Tornado Alley and across the Midwest as a concrete bunker,” said Levitan. “What we’re saying is: How do we take what we know right now and develop those standards so that those who want to design a building to resist some future level of tornado have the technology to do that?”
Communication Is Key
Communications was another important topic in the NIST study. There’s no national standard for safe tornado sirens and they vary by community as does the protocol on how they are used. In some areas, the sirens are left over from the 1950s and designed to warn against nuclear attack. And sirens sound differently in different areas and mean different things. For instance, some communities sound an “all clear,” which means they sound the siren a second time when the hazard is over. But some don’t, and that created a problem in Joplin.
A first siren sounded for a storm on the northern edge of Joplin, but that one didn’t produce a tornado. A second siren sounded to confirm that a tornado had touched down. Some people thought the second siren was an all-clear signal.
One of the recommendations is to develop next-generation warning technology to home in on exactly where the danger to communities lurks. Many communities have the “polygon system,” where a polygon is drawn over certain communities and those are warned of an impending hazard. That’s better than warning by counties, but still not accurate enough because there may be pockets of the community where the hazard is great and some pockets where there may be no hazard at all.
Another problem in Joplin was the lack of a coordinated and consistent message from all broadcast mediums, weather stations and the National Weather Service (NWS). The level of urgency depended on which television station people were watching. In one instance, TV news anchors, not knowing the audio was on, sounded an ominous tone and viewers responded accordingly.
The NIST recommendation for improved communication calls for the “development of national codes and standards and uniform guidance for clear, concise, consistent, recognizable and accurate emergency communications, encompassing alerts and warnings. … NIST also recommends that emergency managers, the NWS and the media develop a joint plan.”
Springboard to Progress
It is hoped the NIST recommendations will lead to breakthroughs for tornado safety nationally. “When you talk to people about this, they really saw Joplin as a springboard toward change on a national basis,” said Keith Stammer, Joplin’s director of emergency management. “While many of those codes may not be implemented here in Joplin, they certainly are a means to try to change the building codes all across the nation.”
But it won’t be easy, Stammer said, at least not in Joplin. Of course, the biggest problem is funding. “Those are expensive items to have to incorporate into your codes,” he said. “To try to find financing to do those sorts of things is difficult.”
Already approved and slated for the 2018 International Building Code are requirements for tornado shelter construction at schools. Any new construction at schools, such as building a gymnasium, will have to include a new shelter if there is ample square footage.
Joplin has received a lot of Community Development Block Grant money from state and local sources that helps with construction, but all that financing comes with qualifications. “You have to adhere to certain building codes and standards, where and how it’s being built, and most of this is low- and moderate-income [housing]. It’s quite a labyrinth to work though state and federal regulations that touch on many of these things.”
Joplin has already made great progress in addressing tornado hazards since 2011. Prior to the tornado, the city had no public storm shelters. Now, every school either has storm shelters or a plan to build them. The shelters are sized so that not just the school population, but also the local neighborhoods — between a quarter- and half-mile radius — can use them. They’ve also deployed automatic unlocking systems on the doors so that the shelters can be available 24 hours a day.
One of the things Joplin didn’t do was require storm shelters in all of its construction. “There was a lot of discussion about that, but the homebuilders association felt that that would be quite the cost,” said Stammer. “Having said that, I’ve noticed that it’s been rather difficult for somebody to sell a newly constructed house or rent newly constructed apartments that don’t have either tornado shelters or access nearby to a group shelter.” He said a lot of homes will have a shelter built into them and apartment complexes will have a shelter for the complex.
Key NIST code recommendations that resulted from the Joplin study include:
• That a capacity be developed and deployed that can measure and characterize actual tornadic wind fields, including near-surface wind fields, for use in the engineering design of buildings and infrastructure. This would require enhancement and widespread deployment of cost-effective, advanced technologies, including weather radar.
• That nationally accepted performance-based standards for the tornado-resistant design of buildings and infrastructure be developed and adopted in model codes and local regulations to enhance the resiliency of communities to tornado hazards. The standards should encompass tornado hazard characterization, performance objectives and evaluation tools. The standards shall require that critical buildings and infrastructure, such as hospitals and emergency operations centers, be designed to remain operational in the event of a tornado.
• The development of risk-balanced, performance-based tornado design methodologies such that all building components and systems meet or exceed the same performance objectives when subjected to tornado hazards. The standards should encompass tornado hazard character.
• That a tornado shelter standard specific for existing buildings be developed and referenced in model building codes; and tornado shelters be installed in new and existing multifamily residential buildings, mercantile buildings, schools and buildings with assembly occupancies located in tornado hazard areas.
• The development of national codes and standards, and uniform guidance for clear, consistent, recognizable and accurate emergency communications, encompassing alerts and warnings, to enable safe, effective and timely responses among individuals, organizations and communities in the path of storms having the potential to create tornadoes.
NIST also recommends that emergency managers, the NWS and the media develop a joint plan and take steps to make sure that accurate and consistent emergency alert and warning information is communicated in a timely manner to enhance the situational awareness of community residents, visitors and emergency responders affected by an event.
• NIST recommends that technology be developed to provide tornado threat information to emergency managers, policy officials and the media on a spatially resolved, real-time basis to supplement the currently deployed official binary warn/no warn system.
