F-Scale NumberIntensity PhraseWind SpeedType of Damage Done
F0Gale tornado40-72 mphSome damage to chimneys; breaks branches off trees; pushes over shallow-rooted trees; damages sign boards.
F1Moderate tornado73-112 mphThe lower limit is the beginning of hurricane wind speed; peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos pushed off the roads; attached garages may be destroyed.
F2Significant tornado113-157 mphConsiderable damage. Roofs torn off frame houses; mobile homes demolished; boxcars pushed over; large trees snapped or uprooted; light object missiles generated.
F3Severe tornado158-206 mphRoof and some walls torn off well constructed houses; trains overturned; most trees in fores uprooted
F4Devastating tornado207-260 mphWell-constructed houses leveled; structures with weak foundations blown off some distance; cars thrown and large missiles generated.
F5Incredible tornado261-318 mphStrong frame houses lifted off foundations and carried considerable distances to disintegrate; automobile sized missiles fly through the air in excess of 100 meters; trees debarked; steel re-inforced concrete structures badly damaged.
F6Inconceivable tornado319-379 mphThese winds are very unlikely. The small area of damage they might produce would probably not be recognizable along with the mess produced by F4 and F5 wind that would surround the F6 winds. Missiles, such as cars and refrigerators would do serious secondary damage that could not be directly identified as F6 damage. If this level is ever acheived, evidence for it migh only be found in some manner of ground swirl pattern, for it may never be identifiable through engineering studies


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