On the Current Revision of the EF-Scale

In 1970, Dr. Tetsuya (Ted) Fujita created a tornado rating system, which he called the F-Scale, based on the severity of building damage (Fujita, 1971, 1973). During the next decade, the National Weather Service (NWS) began using the F-Scale to rate tornado damage intensity from F0 to F5. In the early 2000’s, wind engineering studies revealed mounting evidence that the vast majority of constructed houses can be completely destroyed at wind speeds less than 261 mph (117 m/s), F5 level damage (Phan and Simiu 1998). Led by the Wind Science and Engineering Center (WSEC) at Texas Tech University (TTU) and funded by the Building and Fire Research Laboratory at the National Institute of Standards and Technology (NIST), a team of atmospheric scientists and wind engineers developed the Enhanced Fujita (EF) Scale to address certain limitations and inconsistencies with the F-Scale (WSEC 2006). In 2007, the EF-Scale was adopted by the National Weather Service (NWS). It changed the range of failure wind speeds for specific degrees of damage (DoD) for certain damage indicators (DIs), based on how well a building or object was constructed. While the EF-Scale documentation was a great improvement over the F-Scale, the need for further detail was made apparent by the wide variations in assigned EF-ratings in the Storm Data record (Edwards et al., 2013). Studies also recommended that a committee should be formed to propose, accept, and implement changes to the EF-Scale, including the development of new DIs and use of science-based approaches, (Kuligowski et a., 2014).

In 2014, the American Society of Civil Engineers (ASCE)/Structural Engineering Institute (SEI) and the American Meteorological Society (AMS) undertook an effort to develop a consensus standard for tornado wind speed estimation. The forthcoming ASCE/SEI/AMS standard, Wind Speed Estimation in Tornadoes, will officially standardize the EF-Scale. This paper describes the proposed EF-Scale modifications in detail, which will include much more descriptive information than in the original EF-Scale, more DoDs, more DIs, improved consistency of damage states and wind speeds across DIs, a narrative describing various wind resistance levels of each DI, commentaries for each DI, additional guidance photographs, and references to damage surveys including those conducted during the past 15 years.