Enhanced F (EF) Scale for Tornado Damage

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1 Enhanced F (EF) Scale for Tornado Damage An update to the the original F-scale by a team of meteorologists and wind engineers, implemented in the U.S. on 1 February (from and

2 The Participants Steering Committee Fujita Scale Forum Participants

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4 Fujita Tornado Damage Scale Developed in 1971 by T. Theodore Fujita of the University of Chicago SCALE WIND ESTIMATE *** (MPH) TYPICAL DAMAGE F0 < 73 Light damage. Some damage to chimneys; branches broken off trees; shallow-rooted trees pushed over; sign boards damaged. F Moderate damage. Peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos blown off roads. F F F F Considerable damage. Roofs torn off frame houses; mobile homes demolished; boxcars overturned; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground. Severe damage. Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off the ground and thrown. Devastating damage. Well-constructed houses leveled; structures with weak foundations blown away some distance; cars thrown and large missiles generated. Incredible damage. Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 meters (109 yds); trees debarked; incredible phenomena will occur. IMPORTANT NOTE ABOUT F-SCALE WINDS: Do not use F-scale winds literally. These precise wind speed numbers are actually guesses and have never been scientifically verified. Different wind speeds may cause similar-looking damage from place to place -- even from building to building. Without a thorough engineering analysis of tornado damage in any event, the actual wind speeds needed to cause that damage are unknown.

5 Over the years, the F-Scale has revealed the following weaknesses: It is subjective based solely on the damage caused by a tornado No recognition in difference in construction Difficult to apply with no damage indicators if the 3/4-mile wide tornado does not hit any structures, what F- scale should be assigned? Subject to bias Based on the worst damage (even if it is one building or house) Overestimates wind speeds greater than F3 And the F-Scale has had its misuses over the years: Too much reliance on the estimated wind speeds Oversimplification of the damage description Judge the F-scale by the appearance of the tornado cloud Unrecognizing weak structures mobile homes modified homes

6 The "Modified" Fujita Scale For example, if a tornado knocks down the walls of an area of homes. If it is determined that the walls collapsed, then the damage assigned is F3. If it is a brick home, then that lowers the damage to F2. Then, according to the table since it was a brick structure, then you +1 making the rating F3.

7 The Enhanced Fujita Scale The EF Scale must continue to support and maintain the original tornado database.; In other word, there must be some conformity to that of the F-Scale that is listed in the database. Other ideas were agreed to including: Consistent Assessment of Damage enhance description of damage with examples and photos include not only structures, but also vegetation base damage assignment on more than one structure, if available develop a PC-based expert system develop training materials Data Collection maintain current tornado database surveys should include additional data mean and maximum damage path width basis for damage assignment latitude/longitude of where the path began and ended number of hours spent on the damage survey names of survey team member(s) When using the EF-Scale to determine the tornado's EF-rating, begin with the 28 Damage Indicators. Each one of these indicators have a description of the typical construction for that category of indicator. Then, the next step is to find the Degree of Damage (DOD). Each DOD in each category is given and expected estimate of wind speed, a lower bound of wind speed and an upper bound of wind speed.

8 The Enhanced Fujita Scale FUJITA SCALE DERIVED EF SCALE OPERATIONAL EF SCALE F Number Fastest 1/4- mile (mph) 3 Second Gust (mph) EF Number 3 Second Gust (mph) EF Number 3 Second Gust (mph) Over 200 IMPORTANT NOTE ABOUT ENHANCED F-SCALE WINDS: The Enhanced F-scale still is a set of wind estimates (not measurements) based on damage. Its uses three-second gusts estimated at the point of damage based on a judgment of 8 levels of damage to the 28 indicators listed below. These estimates vary with height and exposure. Important: The 3 second gust is not the same wind as in standard surface observations. Standard measurements are taken by weather stations in open exposures, using a directly measured, "one minute mile" speed.

9 NUMBER DAMAGE INDICATOR ABBREVIATION 1 Small barns, farm outbuildings SBO 2 One- or two-family residences FR12 3 Single-wide mobile home (MHSW) MHSW 4 Double-wide mobile home MHDW 5 Apt, condo, townhouse (3 stories or less) ACT 6 Motel M 7 Masonry apt. or motel MAM 8 Small retail bldg. (fast food) SRB 9 Small professional (doctor office, branch bank) SPB 10 Strip mall SM 11 Large shopping mall LSM 12 Large, isolated ("big box") retail bldg. LIRB 13 Automobile showroom ASR 14 Automotive service building ASB 15 School - 1-story elementary (interior or exterior halls) ES Enhanced F Scale Damage Indicators 16 School - jr. or sr. high school JHSH 17 Low-rise (1-4 story) bldg. LRB 18 Mid-rise (5-20 story) bldg. MRB 19 High-rise (over 20 stories) HRB 20 Institutional bldg. (hospital, govt. or university) IB 21 Metal building system MBS 22 Service station canopy SSC 23 Warehouse (tilt-up walls or heavy timber) WHB 24 Transmission line tower TLT Free-standing tower Free standing pole (light, flag, luminary) FST FSP 27 Tree - hardwood TH 28 Tree - softwood TS

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