Understanding the relationship between structural failure and fatalities in Tornadoes: A quantitative investigation of the 2021 Midwest Tornado Outbreak

During 1950-2011, the number of fatalities caused by tornadoes in the U.S. significantly exceeded the fatalities caused by both hurricanes and earthquakes. To reduce tornado induced fatalities, it is essential to understand how structures/building failures correlate with fatalities and who are more vulnerable to tornadoes. Insights from this study are intended to help provide information to decision-makers on where to allocate limited resources for enhancing tornado resilience. By examining both the fatality data and structural damage data in the 2021 Midwest Tornado Outbreak, the objective of this study is to examine the occurrence of fatalities during tornadoes across various types of building structures and then to establish the correlation between tornado fatalities and structural failure. This study finds that: 1) 72% of fatalities occurred in residential buildings that are mainly wood-framed structures, which stresses the need for improving the performance of residential buildings to tornado effects. Currently, the latest building standards and codes (ASCE7–22 and IBC 2024) do not require a tornado-resistant design for Risk Category II buildings (e.g., residential buildings and some commercial and industrial buildings). With more and more high-intensity tornadoes striking communities, a tornado-resistant design for Risk Category II buildings may be justified; 2) measures should be taken for big-box buildings, especially for those based on concrete tilt-up construction, to reduce fatalities (and injuries); 3) mobile and manufactured homes (MMHs) are vulnerable, even to low-intensity tornadoes, and the data in this study reinforce the known guidance that occupants in MMHs need to evacuate from their MMHs and secure tornado sheltering elsewhere immediately after they receive a tornado warning; 4) fatalities occurred in campgrounds, nursing homes and cars suggest that tornado resistance, tornado resilience, or safety protocols need to be considered for these types of properties. In addition to the preparedness for improving building performance to tornadoes, this study also discusses the risk perception of different stakeholders, sheltering availability, accessibility and protocols, and emergency management to reduce tornado fatalities.