Intended use and potential misuse of the EF Scale

The original Fujita Scale (F Scale) was introduced in the early 1970s as a means of estimating the intensity of tornadoes and hurricanes by relating windspeeds to the appearance of damage. The relationships were based on the extensive experience of Dr. Ted Fujita but were never independently verified. The original F Scale did not account for differences in construction quality and included only a limited number of damage indicators. Three decades later, the Wind Science and Engineering group at Texas Tech University led an effort to improve the original scale, but specifically targeting tornado damage and related windspeeds. The National Weather Service implemented the EF Scale in February 2007 as the official measure of tornado (but not hurricane) intensity. Since the development of the EF Scale, the question has arisen as to whether the EF Scale can be reliably used to predict the amount of wind damage based on known hurricane windspeeds. The need for such a damage prediction tool arises in particular when evidence of wind action is obliterated by severe storm-surge action (as in Hurricanes Katrina and Ike) and it becomes necessary to determine the likely extent of wind damage that occurred prior to destruction of the evidence by storm surge. In contemplating such use of the EF Scale, we examine separately its two major components: (1) degrees of damage and (2) ranges of tornado windspeeds associated with these damage levels. Our experience suggests that the EF Scale properly describes the overall progression of damage with increasing windspeeds in both tornadoes and hurricanes; however, the windspeeds associated with various degrees of damage are expected to be different for structures exposed to hurricanes and tornadoes. Use of the EF Scale to predict hurricane damage based on peak windspeeds is therefore discouraged.