The Enhanced Fujita scale (abbreviated EF-Scale) is a scale that rates tornado intensity based on the severity of the damage a tornado causes. It is used in the United States, Brazil and France, among other countries.[1][2] The EF scale is also unofficially used in other countries, including China.[3] The rating of a tornado is determined by conducting a tornado damage survey. The scale has the same basic design as the original Fujita scale—six intensity categories from zero to five, representing increasing degrees of damage. It was revised to reflect better examinations of tornado damage surveys, in order to align wind speeds more closely with associated storm damage. Better standardizing and elucidating what was previously subjective and ambiguous, it also adds more types of structures and vegetation, expands degrees of damage, and better accounts for variables such as differences in construction quality. An "EF-Unknown" (EFU) category was later added for tornadoes that cannot be rated due to a lack of damage evidence.[4] As with the Fujita scale, the Enhanced Fujita scale is a damage scale and only an estimate for actual wind speeds. While the wind speeds associated with the damage listed did not and have not undergone empirical analysis (such as detailed physical or any numerical modeling) due to expensive costs, the wind speeds were obtained through a process called expert elicitation, which was based on various engineering studies since the 1970s as well as from the field experience of meteorologists and engineers. Unlike the original Fujita scale and International Fujita scale, ratings on the Enhanced Fujita scale are based solely off the effects of 3-second gusts on any given damage indicator.[5]
grabbed straight off of wikipedia
