damage assessment
TRANSCRIPT
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Overview of Damage Assessments
Ron W. PrzybylinskiScience and Operations Officer
NWS St. Louis
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OutlineDamage Patterns (Tornadic andDownburst (Microbursts)Brief review of the EnhancedFujita (EF) ScaleExample – “You Make the Call” What can I do for you. What
can you do for me.
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Why do damage assessments?Determine tornadointensity
Estimate wind speeds
Storm track, width
Determine warningresponse
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Heard this Before?
It sounded like a freight trainThe trees (or whatever) are twistedOnly a tornado could do this muchdamageI felt my ears “pop”
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Tornadic Damage
Convergence pattern – arrows pointing to thecenter axis of the tornadic damage path (Red) .
From Dr. Ted Fujita – Univ. of Chicago
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House trailer damage from a violenttornado – 2:00 am CST
November 6 2007 Evansville IN .
Eastbrook Mobile Home Park – southeast of Evansville Indiana
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View from a plane viewing SE -
Eastbrook Mobile Home Park
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Multiple Vortex Tornado
Multiple Vortex pattern – the strongest winds often occurwith this type of ground pattern (suction vortices) .
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Remains of a corn field from
a violent tornado
Are you able to observe part of a convergent pattern ?
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Downburst clusters
associated with bow echoes
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Small part of a downburst clusterover southern Clinton County
Illinois – July 21 2006
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Characteristic Tornado Downburst
Aspect Ratio Long & thin Short & wide
Damage gradient High Low
Trajectories of debris
Narrow andconvergent
Broad and divergent
Appearance of
damage
Chopped up, chaotic Laid out neatly
Visual clues fromground
Swirls, mudsplattered on walls
No swirls, no mud
Visual clues fromaircraft
Vortex mark Starburst pattern
Damage characteristics we
look for:
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Introduction to theEnhanced Fujita (EF) scale
Dr. Ted Fujita (1971) developed the Fujitascale to provide a method to rate the
intensity of tornadoes.However after 33 years of using the Fujitascale, users have found many limitations tothis scale (e.g. lack of damage indicators ).In many cases NWS personnel would overestimate the wind speeds with tornadoes.
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Enhanced Fujita (EF) scale
Steering committee (23 members)developed the following:Identify “Damage Indicators.” Correlate appearance of damage towind speedPreserved the historical data baseSeek additional input from users
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EF Scale vs. Traditional FujitaScale Wind Speed Ranges
Fujita Scale wind mph EF Scale wind mph
3-Second Gust 3-Second Gust
F0 45 - 78 EF0 ≤ 85
F1 79 - 117 EF1 86 – 110
F2 118 - 161 EF2 110 – 135
F3 162 - 209 EF3 136 – 165
F4 210 - 261 EF4 166 – 200
F5 262 - 317 EF5 ≥ 200
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28 Damage Indicators
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One-and Two-FamilyResidences (FR12)
Typical Construction: Asphalt shingles, tile, slate or metal roof coveringFlat, gable, hip, mansard or mono-sloped roof or
combination thereof Plywood/OSB or wood plank roof deck Prefabricated wood trusses or wood joists and rafterconstruction
Brick veneer, wood panels, stucco, EIFS, vinyl or metalsidingWood or metal stud walls, concrete blocks or insulatingconcrete panels
Attached single or double garage
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One-and Two-FamilyResidences (FR12)
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One-and Two-Family ResidencesDegree of Damage (DODs)
DOD Damage Description Exp(mph)
LB(mph)
UB(mph)
1 Threshold of visible damage 65 53 80
2 Loss of roof covering material (<20%), gutters and/orawning; loss of vinyl or metal siding 79 63 97
3 Broken glass in doors and windows 96 79 114
4 Uplift of roof deck and loss of significant roof coveringmaterial (>20%); collapse of chimney; garage doorscollapse inward or outward; failure of porch or carport 97 81 116
5 Entire house shifts off foundation 121 103 141
6 Large sections of roof structure removed; most wallsremain standing 122 104 142
7 Exterior walls collapsed 132 113 153
8 Most walls collapsed, except small interior rooms 152 128 173
9 All walls collapsed 170 142 198
10 Total destruction of entire building, slab swept clean 200 165 220
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One-and Two-Family Residences
FR12: DOD4: Uplift of roof deck and loss of roof covering (>20%);garage door collapses outward (LB 81 mph; UB 116 mph; Exp 97 mph)
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One-and Two-Family Residences
FR12: DOD7: Top floor (First floor in this case) exterior wallscollapsed. (LB 113 mph; UB 150 mph; Exp 132 mph).
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One-and Two-Family Residences
FR12: DOD10: Total destruction of entire building(LB 165 mph; UB 220 mph; Exp 200 mph).
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Recommended steps forassessing tornado damage
Conduct a survey (aerial if possible)Select several damage indicators (trees, buildings,
power poles, etc…) that tend to indicate the highestwind in the damage path Assign an EF-scale to individual DIs – documentRate the tornado intensity by applying the highestrated DI, provided there is supporting evidence of similar damage nearby.Document the basis for assigning the EF-Scale, and
record other pertinent data related to the event
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Structures’ Response to Wind
Type
DesignOrientation of structure to the windsThe upstream terrain
Duration and gustiness of the windMissiles
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Pressure on the building’s interior increases, resulting inadditional outward forces. That is why opening windows isnot a good idea.
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Failure Points
Rafter/top plateRoof joist/top
plate
Wall stud/bottomplateWall/foundation
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You make the call
Large Industrial building
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Another Image
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Remains of a corn field
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What can I do to help you out?
What can you do to help me out?
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