12/8/16
Tree Risk Assessment
BMP and TRAQ Update:
What is going to change?
Tom Smiley,
Sharon Lilly,
Nelda Matheny
ANSI, Risk BMP, & TRAQ
ANSI A300 Part 9 Risk
Publication expected early
2017
Tree Risk Assessment BMP
Second edition in process,
anticipate fall 2017 release
TRAQ 2.0
Manual and course have been
revised, will be released in
October 2017, Cost & Process
Changes in the Risk
Assessment BMP
üLevel 1 additional guidance
üWeather categories clarified
üTime frame – can use multiple
üLikelihood of Failure –
definitions tweaked
üLikelihood of Impact – Medium
modified
üWhat risk are we defining?
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Level 1 – Additional Guidance
One or more of the three factors
remains constant
• Likelihood of failure
• Likelihood of impact
• Consequences of failure
Level 1 – Example
Street Tree Management
For a Level 1 of street
trees like this, what can we
hold constant?
Constant Factors
• Likelihood of Impact
Medium
• Consequences of
failure
Severe
Variable Factor
• Likelihood of Failure
• Imminent
• Probable
Level 1 – Example
Street tree management
• Fixed Factors
• Likelihood of impact – Medium
• Consequences of failure - Severe
Likelihood
of Failur e
Likelihood of Impacting Target
Ver y Low
Im m inent
Unlikely
Pr obable
Unlikely
Possible
Unlikely
Im pr obable Unlikely
Low
Medium
Som ewhat Likely
likely
Unlikely
Som ewhat
likely
Unlikely
Unlikely
Unlikely
Unlikely
High
Ver y
Likely
Likely
Som ewhat
likely
Unlikely
Lik e lihood of
Consequences of Tree Failure
Fa ilure & Im pa c t
Ne gligible
Minor
Signific a nt
Se v e re
Ve ry Lik e ly
Low
Mode ra te
High
Ex tre m e
Lik e ly
Low
Mode ra te
High
High
Low
Low
Mode ra te
Mode ra te
Low
Low
Low
Low
Som e wha t
Unlik e ly
lik e ly
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12/8/16
Level 1 – Example
Street tree management
• With those two fixed factors
An Imminent LoF rating results in High risk rating
A Probable LoF rating results in Moderate risk
rating
Likelihood of
Failur e
Risk r ating when
Lof Im pact is Medium
And
Consequences ar e Sever e
Im m inent
High
Pr obable
Moder ate
Possible
Low
Im pr obable
Low
Level 1 Example for an
Electrical Utility
Fixed factor
Consequences
Significant
Variable factors
Likelihood of Impact
High
Medium
Likelihood of
Failure
Imminent
High
Weather Classification
•Normal
•Extreme
•Abnormally
Extreme
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12/8/16
“Normal” Weather
We assess trees
considering “normal”
weather (10-30 year
average)
May include infrequent, but
recurring severe weather
and storms
Would not include
“abnormally extreme”
storms, tornados,
hurricanes, or freezing rain
“Normal” Weather at BOS
• Normally (every year)
BOS has sustained
wind to 40 mph
• Probable trees may
be expected to fail
38 mph
BOS Wind Rose 30 year
“Extreme” Weather at BOS
• Sustained winds
40-55 mph,
• Possible trees
may be expected to
fail
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12/8/16
“Abnormally Extreme” Weather
at BOS
• Strongest Gusts
recorded at BOS 94
mph
• Sustained winds >55
• Freezing rain
• Any tree, including
Improbable, can fail
• Doesn’t mean that
every tree will fail.
Emphasis on Time Frame
• Likelihood of failure is meaningless
without a stated time frame
• BMP will have an increased
emphasis
• TRAQ will reinforce the concept
• May assess for more than one time
frame
• Time frame is not necessarily the
same as the inspection interval
Time Frame
Time period for which
an assessment is
defined.
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12/8/16
Different Time
Frames result in
Different Ratings
•One year – Possible
•5 year - Probable
Likelihood of Failure
Definitions Clarified
Imminent
Failure has started or is
most likely to occur in
the near future, even if
there is no significant
wind or increased load.
The imminent category
overrides the stated time
frame.
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12/8/16
Probable
Failure may be
expected under
normal weather
conditions within the
specified time
period.
Possible
Failure may be
expected in extreme
weather, but it is
unlikely during
normal weather
conditions within the
specified time frame.
One root with Inonotus
Improbable
Failure is not likely
during normal
weather and it may
not fail in extreme
weather within the
specified time frame.
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12/8/16
Likelihood of Impact
• Unchanged: High—The failed tree
or branch will most likely impact the
target.
• Old Medium -The failed tree or
branch may or may not impact the
target, with nearly equal likelihood.
• New Medium - The failed
tree or branch could impact
the target, but is not
expected to do so.
Defining the Risk
• Typically several
different risks are
assessed
• Different targets
• Different failure
modes
• Each row of the TRA
form’s chart represents
a distinct risk
• Each must be clearly
defined
Defining Each Risk
Time fr ame = 3 ye ar s
Branch
Dead
8”
35’
1
people
none
x
x
x
x
High
“My assessment indicates that the risk of the
dead branch on the north side of the tree failing
and hitting a person and causing severe injury
within the next 3 years is high.“
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12/8/16
Defining Each Risk
Time fr ame = 1 ye ar s
Roots
20% de caye d
4 8” 55’
1
none
x
x
x
x L ow
“My assessment indicates that the risk of rootrelated, whole-tree failure leading to personal
injury within the next year is low.”
TRAQ Exam will include brief statement of what
the risk is that you are defining
TRAQ
Qualification and
Requalification
TRAQ Requalification is
Required 5 years after
completing your initial class
There are no CEUs to maintain the Qualification
But you do get CEUs for taking the class
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12/8/16
TRAQ Timetable
• The first full TRAQ
qualifications expire in
Spring 2018
• New version (TRAQ 2.0)
training starts October 2017
• May Requalify four years
after full class or up to 6
months after expiration.
• Expiration date will not
change.
TRAQ 2.0 Qualification Course
Parameters remain the same
2 days of class + ½ day written +
practical exam
Content changes to match BMP
Same level of hands-on learning
No more pre/post tests
More practice time
TRAQ 2.0 Requalification
• 1-day Review of major concepts and new
material
• Does not include all of the items on the exam
• Same exams and passing scores
• 5 hrs instruction, 3 exam
• Up to 30 people per class
• $210/$250 tuition
• Option to retake the
full course
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12/8/16
New Datasheet will
come with TRAQ
Revisions and
Requalification
•Available free online in
October 2017
•Some items rearranged
for easier use.
•Added second Branch
L of F classification line
•Target description space
to second page table
Questions?
[email protected]
Risk Assessment
Research
•Existing methodologies
•Scholarly publications
•Scientific journal, Risk Analysis
•Public Safety and Risk Assessment
- David Ball and Laurence BallKing
•Arboriculture & Urban Forestry
•Risk assessment experts
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12/8/16
Risk Assessment Standards
•ISO 31010 – Risk ManagementRisk Assessment Techniques
•AS/NZS ISO 31000:2009
Risk management—Principles and
guidelines
•American National Standards
Institute (ANSI) A300
part 9 – Risk Assessment
•UK National Tree Safety Group
(NTSG)
Quantitative or Qualitative
• Quantitative assessment
• Estimates values based on
Risk = Probability x Consequences
• None is use in arboricultural context
• Qualitative assessment
• Ratings of risk, typically based on
likelihood and consequences
• Pseudo-quantitative
• factor x + factor y + factor z = risk
rating
Matrix Approach
• National and international
standards
• Corporate governance
• Homeland security
• Airport safety
• Sarbanes-Oxley act
• Risk management
software
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12/8/16
Matrix Advantages
• Clear, systematic
framework
• Convenient
documentation of
rationale
• Relatively simple
inputs and outputs
• Requires no
calculations
• Need not quantify
consequences
Consequences
Lik e lihood of
of Tr ee Failur e
Fa ilure & Im pa c t
Ne gligible
Ve ry Lik e ly
Low
Lik e ly
Low
Minor
Mode ra t
Signific a nt
Se v e re
High
Ex tre m e
e
High
High
Low
Mode ra t
Low
Mode ra te
Mode ra te
Low
Low
Low
Low
e
Som e wha t
Unlik e ly
lik e ly
Matrix Limitations
• High subjectivity in rating
factors
• Low resolution
• Not necessarily
comparable to risk
assessed using other
methods
Further Research
• Scholarly publications
• Advantages and limitations of
matrix methodology
• Alternative methodologies
• Risk assessment experts
• Dr. Seth Guikema
• Dr. Tony Cox
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12/8/16
Review of the Current
BMP Methodology
Likelihood of Im pacting
Likelihood of
Failur e
Ver y Low
Low
Medium
:
Likely
Tar get
High
Im m inent
Unlikely
Som ewhat
likely
Pr obable
Unlikely
Unlikely
Som ewhat Likely
likely
Ver y Likely
Possible
Unlikely
Unlikely
Unlikely
Som ewhat
likely
Im pr obable
Unlikely
Unlikely
Unlikely
Unlikely
Consequences
Likelihood of
Negligible
Minor
Failur e &
Im pact
of Tr ee Failur e
Ver y Likely
Low
Moder ate
High
Extr em e
Likely
Low
Moder ate
High
High
Som ewhat
likely
Unlikely
Low
Low
Moder ate
Moder ate
Low
Low
Low
Low
Significant
Sever e
Table 1:
Likelihood
matrix
-likelihood of
the event
occurring
Table 2:
Risk matrix
-categorizing
tree risk
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