SAFMEA Qualitative method for risk analysis

CZECH TECHNICAL UNIVERSITY IN PRAGUE
Faculty of Transportation Sciences
Department of Transporting Systems
SAFMEA
Qualitative method for risk analysis
Jan Michek
[email protected]
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Introduction
 One of universal methods used for assistance with decision making
can be risk analysis.
 The risk means presumable loss value created by realization of
danger and expressed in money or another units.
 Domain of risk analysis, as a part of risk engineering, is the most
elaborated in the banking and insurance business.
 There are used methods like FMEA (multi-criterion analysis of
trouble process and failure consequences) or UMRA (working with
general-purpose risk matrix).
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Introduction
 Process of risk analysis run in several steps:
 Identification of danger (project segments and sources of peril, which
menace them)
 Risk qualification (risk differentiate according to their importance)
 Risk quantification (loss frequency and importance expressed e.g. in money,
fatalities etc.)
 Expert methods take advantage of experts’ experiences or entire
expert team’s knowledge.
 Expression of estimated danger and risks can be:
 verbal (arbiter gains colorful set of information)
 numerical (arbiter obtains unambiguous base; is allows comparison for
several project alternatives)
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Terminology
 Expert Judgment – a group of experts assesses certain risk. Quality
of this assessment depends on their experiences and ability to
deduce relevant conclusions from their evaluation
 Qualitative Risk Analysis – suite of methods for safety assessment,
which uses verbal assessment of reasons and results
 Quantitative Risk Analysis – systematic attitude for prediction of
accident frequency and impacts on facilities or system functions
 Check List – qualitative tool used to prior specified equipment
evaluation and condition reviewing
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FMEA
 = Failure Mode and Effect Analysis
 Basic method for qualitative analysis based on experts’ experiences
 For the first time used in 1949 in US Army directive Mil-Std-1629
for risks related to military systems malfunctions
 In ‘60 used by NASA in Program Apollo
 It is implemented in many standards (QS-9000-1998, ISO/TS
16949:2002, ČSN IEC 812, 1992)
 This method has two phases:
 Verbal – identification of risk possible genesis and consequences, based on
brainstorming or experts’ correspondence
 Numerical – for individual risks perform experts numerical estimation of
their parameters and they express it in relative integer scale
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FMEA
 For danger impact of assessment of ith project segment there is a
relative coefficient RPNi
RPN  Sv  Lk
 RPN - Risk Priority Number
 Sv – danger importance (Severity)
 Lk – probability of danger realization (Likelihood)
 Sum for partial RPN hasn’t any factual meaning, but it is possible
to use it while more alternatives of one project are compared
 Coefficient RPN can be generalized with information about failure
observability, however it is very poorly detectable in practice
 Dt – failure observability (Detection)
RPN  Sv  Lk  Dt
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SAFMEA
 = Statistically Adjusted Failure Mode and Effect Analysis
 Classic FMEA method advanced in statistical interpreting of numerical
assessments RPN – it takes random variability of experts’ assessments
into consideration.
 In contrast to FMEA, there is for each row in form determined ne expert
values of RPN index, from which the mean value and standard deviation
of variance are calculated. Maximal deviations in expert assessments are
reviewed in detail or simply ignored.
 Example – risk evaluation of 3 project alternatives of communication
construction
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Alternative
Description
V1
Surface communication construction
V2
Surface construction combined with tunnel
V3
Fully tunneled alternative
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SAFMEA I
 Stage 1 – Preparation
 Risk analytic selects project aspects for which risk rate will be evaluated.
 Expert team is putted together from experts coming from a lot for diverse
branches. For a bigger group there is a smaller statistical deviation. Minimal
number of team members is ne = 3, optimal number is ne > 5.
 The best would be if the domain of risk engineering is well-known to the
risk analytic and if he/she is informed about project issues.
 Risk analytic ensures coordination for team activities.
 In each project stage it is possible to use another expert team (e.g. one team
for a form creation and the second one and bigger for filling the form in)
 Example – choice of expert team members
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Organization
Abbreviation
Name
Email
CTU Faculty of Transportation Sciences
FD
prof. Ing Pavel Přibyl, CSc.
[email protected]
CTU Faculty of Transportation Sciences
FD
Ing. Jan Michek
[email protected]
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SAFMEA II
 Stage 2 – Risk segments and risk factors definition
 Experts select project segments, which can be menaced by some risk (e.g.
construction, financing, safety etc.)
 Fro individual segments concrete risk factors (RF) are determined (e.g.
finishing project after deadline, exceeding planned budget, etc.).
 The output of the expert team cooperation is a form.
 Example – definition of one project segment and its risk factors
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Segment
Influence on vicinity and construction duration
RF1
Increased costs for environment and residence function protection
RF2
Noise and vibration exposure during construction
RF3
Atmosphere pollution during construction
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SAFMEA III
 Stage 3 – Expert assessment of risk factors
 Risk analytic suggests a metric for risk factors evaluation and supplements
columns for parameters of severity Sv and likelihood Lk of its emergence
into the form.
 The scales for individual parameters (Sv, Lk) can varies, in order to retain
risk weight contained in RPN index while multiplying them to each other.
 Experts perform evaluation of individual risk factors according to their
opinion and a in compliance with their importance and probability of
occurrence assign a value from matching scale to the parameters.
 A part of the form is also an instruction how to fill it in: if the expert doesn’t
understand definition of risk factor or he/she isn’t sure about the answer,
he/she must skip evaluation of this point.
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SAFMEA III
 Example – severity evaluation scale
Sv – Risk importance
Impact on project
Numerical
evaluation
unimportant for construction and performance
insignificant
1
delay of deadlines, financial requirements increase and environmental impacts are minimal
small
2
delay of deadlines, financial requirements increase and environmental impacts are around 10
percents
big
8
incurred damages affect construction and performance radically
critical
16
 Example – likelihood evaluation scale
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Numerical
evaluation
Lk – Risk likelihood
Occurrence probability
cannot expect
improbable
1
very small
little probable
2
can expect
very probable
3
arise
sure
4
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SAFMEA IV
 Stage 4 – RPN index interpretation
 For each row j (RF) we obtain ne expert values Sv and Lk from forms filled
by all k experts. From this values final RPN indexes are calculated
RPN Ejk  Sv Ejk  Lk Ejk
 For each RF the mean value is calculated
ne
mRPN Ej 
 RPN
k 1
E
jk
ne
 If ne > 5 we can determine the standard deviation of variance
sRPN Ej 
1
E
E 2

RPN

mRPN

jk
j 
ne  1 k
 It is also suitable to compute estimated distribution quantile, which gives
imagine about index randomness
qRPN Ej  mRPN Ej  sRPN Ej
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SAFMEA IV
 The maximum value of risk severity maxSvEjk for expert k is found, because
the most important risks would be omitted. The reason to do this is that the
most serious accidents are very little probably and in RPN index these don’t
occur as very risky events.
 Example – railroad train derail
on the bridge is very little
probably (Lk = 1), but very
serious (Sv = 16). The resulting
RPN is 16, which isn’t any
extreme value of risk.
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SAFMEA V
 Stage 5 – Manners and consequences assessment
 Final mathematical assessment is ordered by mean value mRPNEj
descending.
 It is important to show standard deviation and number of assessing experts.
 Thus ordered rows are used to suggest steps to overall risk reduction.
Project component
Failure type
Failure consequences
activity
item downfall into tunnel access lane
traffic halt
activity
terrorist attack in tunnel (set a tire on fire)
person
suicidal behavior
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mRPN
sRPN
qRPN
n
20
15,33
35,53
8
damage of tunnel technology
17,43
16,52
33,95
7
crash with vehicle
17,33
5,47
22,8
8
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SAFMEA V
 Example – mean values mRPN for 69 risk factors
–––– mRPN > 16 … RF evaluated as conditionally acceptable
–––– mRPN > 32 … RF evaluated as critical danger
 Example – mean values mRPN for 69 RF ordered descending. There is visible in
the chart, approximately 1/3 RF are risky and around 1/3 RF are critical for
project success.
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SAFMEA V
 Example – list of risk factors (tunnel construction project)
 Risk of incongruity with municipal plan
 Risk of danger for cultural/natural sights
 Risk of increased noise and vibration exposure during the construction
 Risk of increased noise and vibration during performance
 Risk of traffic safety for drivers
 Risk of tailback formation
 Danger of accidents
 Possibility of fire
 Risk of construction costs increase
 Risk of shift of start operation date
 Risk of operating costs increase
 Risk of technical viability of plan
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SAFMEA VI
 Stage 6 – Closing assessment
 Performed by risk analytic on acquired and evaluated data basis
 Domains of risk acceptability are selected on mRPN criterion basis
Risk evaluation
Event formation likelihood Lk
Event severity Sv
1
2
3
4
16
16
32
48
64
mRPN
Risk significance
1-8
Risk is acceptable
8
8
16
24
32
16 - 24
2
2
4
6
8
32 - 64
1
1
2
3
4
Risk is conditionally
acceptable
Risk is unacceptable
 If the scale is linear, risk factor with big probability of occurrence but with
minor impact (4x1) would be assessed equally as factor with improbable
occurrence but with critical consequences (1x4).
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SAFMEA VI
 Example – 3 RF evaluation for 3 project’s alternatives
Risk evaluation
Event formation likelihood Lk
Event severity Sv
1
2
3
16
V1/RF2; V3/RF3
V3/RF2
V3/RF1
V1/RF3
V2/RF1; V2/RF3
V2/RF2
4
8
2
1
V1/RF1
 Example – commented rating
Alternative
Comment
Result
V1
Building the route as surface communication is conditionally risky
just in case of noise and vibration exposure to vicinity
suit
V2
For alternative, where the route goes through the tunnel in the
area of housing development, no factors are risky
suit
V3
For the tunnel alternatives all risk factors are risky, 2 of them
even critically
doesn’t suit
 Conclusion – alternatives 1 and 2 seem to be acceptable
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Imperfections of SAFMEA
 Inaccurate assignment
 Effort to supply identically structured and detailed input data
 Lack of information
 It is possible to put forward comments and questions on the first meeting
 Incorrect or misleading information
 Following communication is under correspondence way (due to influence)
 Uncertainty of results
 For a bigger expert team there is a smaller statistical deviation
 One-sidedness of view on project
 There must be represented different branches in the expert team
 Evaluator’s irresoluteness
 Experts must not assess risk factors, in which they don’t understand
assignment or they haven’t enough experiences
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UMRA
 = Universal Matrix of Risk Analysis
 Verbal phase – initial matrix form with endangered parts of project
and danger sources
 Numerical phase – estimations of danger importance using logicalnumerical scale are filled into initial matrix form
 Expert matrix – initial matrix form with severity coefficients Sv
filled by one expert
 Final matrix – calculated from evaluation from all experts matrices
and it express information about individual risk factors
dangerousness
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Conclusion
 SAFMEA method allows qualitative comparison of more project
alternatives using one measured variable – the risk.
 The risk means presumable loss value created by realization of
danger and expressed in money or another units.
 According to analysis results it is also possible to find the most
risky factors for the given alternative and focus on reducing of
potential danger for this factors.
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Example: City Bypass Pelc Tyrolka – Balabenka
(Risk factors)
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Example: City Bypass Pelc Tyrolka - Balabenka (alternative 1)
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Example: City Bypass Pelc Tyrolka - Balabenka (alternative 1)
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Example: City Bypass Pelc Tyrolka - Balabenka (alternative 2)
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Example: City Bypass Pelc Tyrolka - Balabenka (alternative 2)
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Example: City Bypass Pelc Tyrolka - Balabenka (alternative 3)
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Example: City Bypass Pelc Tyrolka - Balabenka (alternative 3)
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Sources
 Přibyl P., Neubergová K., Čarská Z.: Analýza rizik vedení
městského okruhu a Libeňské spojky, ČVUT 2009
 Karásková S.: Risk Analysis in Traffic Engineering
 http://en.wikipedia.org/wiki/Failure_mode_and_effects_analysis
Thank You for Your attention
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