For decades, there was a belief that tornadoes were simply too powerful for even the best-designed buildings to withstand. Tornadoes are deadlier per year than hurricanes and earthquakes combined — but American building codes lacked design requirements to help structures withstand the often abrupt and usually powerful windstorms.
That belief still prevailed when Long Phan joined the National Institute of Standards and Technology (NIST) more than 40 years ago. Tornadoes were causing property damage and death because “engineers thought tornado windspeeds were so high, there’s no way we can economically design structures to withstand them,” said Phan.
Around 1997, Phan and his NIST colleagues re-examined that thinking. They hypothesized that the way we were measuring tornado severity — known as the Fujita Scale — overestimated their strength. Phan and his team investigated a tornado in Jarrell, Texas, that caused severe damage. They discovered that most tornadoes have windspeeds below 135 miles per hour, while the most severe tornadoes can reach windspeeds of more than 300 miles per hour. This led to the Enhanced Fujita System and a new focus on designing structures to withstand winds up to 135 miles per hour.
They realized that most of tornadoes that landed — thus most of the tornadoes causing damage and death — were mid-level storms. So instead of trying to design buildings to withstand the strongest tornadoes, they could prevent most of the damage by creating building standards for the manageable mid-level storms.
Marc Levitan joined Phan at NIST in 2011 and, shortly thereafter, they teamed up to lead a long-term investigation into the deadliest tornado disaster on record (since official recordkeeping on tornadoes began, which goes back to 1950) in Joplin, Missouri. They observed that the tornado had left intact an entire floor of a completely damaged building in a hospital complex, thanks to its impact-resistant exterior windows, suggesting that buildings could be designed to resist them.
They worked with local communities, industry leaders, and researchers to develop a plan to reduce the impacts of future tornadoes, eventually recommending NIST create national standards encompassing their work.
After years of the NIST team’s tireless effort, the 2024 edition of the International Building Code (IBC) unanimously adopted and included its first-ever requirements for tornado resistance. Thanks to the efforts of Phan, Levitan, and their NIST colleagues, the IBC blueprint that most jurisdictions use to create local building regulations will enforce securing structures against the danger of tornadoes.
The “Tornado Wind Loads Team” from NIST also played an essential role in the development of the standards. The team consists of engineers, scientists, and support staff from NIST, as well as numerous people from other federal government agencies, academia, and the private sector. Their work included investigating the tornado in Joplin and a similarly damaging event in Moore, Oklahoma, in 2013.
They also had to research tornado hazards to improve our understanding of the effects on buildings and collaborate with codes and standards committees to translate the research into building code provisions. The team analyzed more than 60 years’ worth of National Weather Service data to examine where and how often tornadoes occur and how they affect buildings, conducted wind tunnel experiments to determine how miniature buildings responded to small-scale vortices, and verified those results with real-world data.
Their work, combined with economic analyses, proved that designing for tornadoes that rate 0 to 2 on the five-point Enhanced Fujita Scale (EF0 – EF2) would protect people from most of the tornadoes in the U.S. In other words, the more violent EF3 – EF5 tornadoes were exceedingly rare in comparison. They also showed that meeting these design standards in building would be economically feasible. To introduce the new standards into the building code, Phan and Levitan hosted workshops and meetings to advance proposals through the American Society of Civil Engineers, which publishes the standard that engineers use to calculate design loads for buildings and other structures.
In September 2024, Phan and Levitan received the Samuel J. Heyman Service to America Medal in the category of Science, Technology, and Environment. The “Sammies,” as they are affectionately known, award Partnership for Public Service medals each year to candidates from across the federal government in seven categories who are selected in recognition of innovative efforts to save lives and deliver critical services to the public.
Creating the world’s first tornado-resistant building codes certainly qualifies. The work of Phan and Levitan will lead to countless lives saved and extensive property damage avoided in critical facilities like schools, hospitals, and nursing homes. Thanks to their decades of work, builders have the tools to erect structures that can withstand 97% of the roughly 1,200 tornadoes that occur in the U.S. each year.
These new codes will apply to all new critical facilities and high-occupancy buildings, like theaters. The team is now working to extend these codes to single-family housing. No longer are tornadoes simply too severe, random, and expensive to plan for — we can build our buildings to survive most tornadoes and put an end to one of Mother Nature’s most unpredictable tricks.