Decommission in The US
The Fujita scale, introduced in 1971 as a means to differentiate tornado intensity and path area, assigned wind speeds to damage that were, at best, educated guesses. Fujita and others recognized this immediately and intensive engineering analysis was conducted through the rest of the 1970s. This research, as well as subsequent research, showed that tornado wind speeds required to inflict the described damage were actually much lower than the F-scale indicated, particularly for the upper categories. Also, although the scale gave general descriptions for the type of damage a tornado could cause, it gave little leeway for strength of construction and other factors that might cause a building to receive higher damage at lower wind speeds. Fujita tried to address these problems somewhat in 1992 with the Modified Fujita Scale, but by then he was semi-retired and the National Weather Service was not in a position for the undertaking of updating to an entirely new scale, so it went largely unenacted.
In the USA and some other countries, on February 1, 2007, the Fujita scale was decommissioned in favor of what these scientists believe is a more accurate Enhanced Fujita Scale, which replaces it. The EF Scale is thought to improve on the F-scale on many counts—it accounts for different degrees of damage that occur with different types of structures, both man-made and natural. The expanded and refined damage indicators and degrees of damage standardize what was somewhat ambiguous. It also is thought to provide a much better estimate for wind speeds, and sets no upper limit on the wind speeds for the strongest level, EF5. Several countries, including Canada and France, continue to use the original Fujita Scale. Environment Canada plans to implement the EF scale in Canada as early as 2013.
Read more about this topic: Fujita Scale