SCAP: A New Methodology for Safety Evaluation and Control Measure Design

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SCAP A New Methodology for Safety Evaluation and
Control Measure Design

• Faisal I Khan
• Faculty of Engineering Applied Science

St Johns, Newfoundland, Canada, A1B 3X5
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What may happen
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What may happen
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What may happen
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What Risk Analysis Can Do?

• Helps in
• Forecasting any unwanted situation
• Estimating damage potential of such situation
• Decision making to control such situation
• Evaluating effectiveness of control measures

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Outline of presentation

• Definitions of Risk and Hazard
• Acceptable Risk Criteria
• Risk Assessment Methodologies
• SCAP a New Methodology
• Application of SCAP to Offshore process facility

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Hazard

• Hazard It is a measure of harm/loss or potential
  of an event to cause harm/loss
• Fire Hazard
• Explosion Hazard
• Toxic Hazard
• Corrosive Hazard
• Radioactive Hazard
• Impact hazard

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Risk

• The probability of suffering a harm or loss.
  It is a combination of Hazard and Probability
• Risk Probability of occurrence of hazard X
  Magnitude of hazard
• Type of Risks
• Background risk
• Incremental risk
• Total risk
• Measurement of Risk (human)
• Individual risk
• Societal risk

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Individual Risk

• Risk posed by an individual
• It is generally measured in time domain for a
  particular type of hazard.
• Risk of death due to fire in an industry
  1.0E-05 /yr

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Societal Risk

• Risk for a group of people
• It is measured in terms of number of people
  exposed to particular risk for a given period of
  time
• Risk of death of 10 workers due to fire in an
  industry 1.0E-09 /yr/10 persons

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Acceptable Risk

• Risk acceptable to regulatory agency and also to
  the public
• Level of Risk of Death Per Year (voluntarily
  acceptable by public)
• Smoking 30 cigarettes per day, 1 in 200
• Man aged 35-44, 1 in 600
• Motor Vehicle Accident, 1 in 10 000
• Accident at home, 1 in 12 000
• Rail accident, 1 in 420 000

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Acceptable Risk Criteria

• UK Health and Safety Executive Criteria FAR
  (Fatality Accident Rate)
• Number of fatality in life time working in an
  industry
• FAR (Number of fatalities)108/(Total hours
  worked by all employees during period covered)
• Acceptable FAR value is 1.0

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Acceptable Risk Criteria

• US EPA
• For carcinogens/or other events a lifetime risk
  of 1 in million (1.0E-06) is considered
  acceptable
• For non-carcinogens a hazard index less than 1.0
  is considered acceptable
• (Hazard index exposed concentration/
  reference dose)

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Acceptable Risk Criteria

• Dutch acceptable risk criteria

Frequency of event
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As Low As Reasonably Practicable (ALARP)
Tolerable only if risk reduction is impracticable
or cost is grossly in proportionate to the
improvement gained
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Methodologies available for safety evaluation and
hazard assessment

• Hazard index Dow index, Mond index
• Hazard and operability (HAZOP) study
• Failure mode effect analysis
• What-if analysis
• Fault tree analysis
• Event tree analysis
• Consequence analysis

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Do we need a new methodology?
fkhan

• No single methodology is able to answer
• What may go wrong?
• How it may go wrong?
• How likely its occurrence?
• What would be the impacts?
• What control measures would reduce its impact and
  likelihood of occurrence?

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A new methodology SCAP

• S- Safety, CA- Credible Accident, and
  P-Probabilistic hazard assessment
• SCAPs objectives
• to identify hazards in an unit/industry,
• to quantify its probability of occurrence,
• to forecast its impacts in and around the
  industry,
• to suggest safety measures and then reassess the
  risk incorporating suggested control methods.

Khan, F.I., Husain, T., Abbasi, S.A., J of
Loss Prevention in Process Industries, 15,
129-146, 2001
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SCAP is developed by integrating

• Safety Weighted Hazard Index (SWeHI),
• Maximum Credible Accident Analysis, and
• Probabilistic Hazard Assessment.

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What may go wrong?
What would be the impacts?
Start
How it may go wrong? How likely its occurrence?

• Hazard identification
• SWeHI

Probabilistic hazard assessment-ASM
Quantitative hazard assessment- MCAA

• Accident scenario development
• MCAS

What control measures would reduce its impact and
likelihood of occurrence?
Fault tree development
Fault tree for the envisaged scenario

• Consequences analysis
• MAXCRED

• Fault tree analysis
• PROFAT

Apply safety measures and re-evaluate risk
Risk estimation
Whether risk is in acceptance?
Suggest safety measures to control risk
No
Yes
End
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Start

• Hazard identification
• SWeHI

Probabilistic hazard assessment-ASM
Quantitative hazard assessment- MCAA

• Accident scenario development
• MCAS

Fault tree development
Fault tree for the envisaged scenario

• Consequences analysis
• MAXCRED

• Fault tree analysis
• PROFAT

Apply safety measures and re-evaluate risk
Risk estimation
Whether risk is in acceptance?
Suggest safety measures to control risk
No
Yes
End
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Safety weighted hazard index (SWeHI)

• It relates hazards posed by a unit and safety
  measures effective on it
• It represents the radius of the area of 50
  probability of fatality/damage

Khan F.I., Husain, T., and Abbasi, S.A.
Transaction of IChemE UK, B79, 1-16, 2001
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SWeHI continued

• SWeHI B/A
• B is the quantitative measure of the damage
  potential
• A represents the credits due to control measures
  and safety arrangements

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Start
Manageable units take one unit
Identify all hazardous chemicals
Type of hazards presents?
Fire and explosion hazards
Toxic and Corrosive hazards
Match the unit with the predefined units
Calculate G factor
Calculate penalties
Calculate Fs factor and different penalties
Estimate damage potential
Estimate damage potential using Fs penalties
Estimate B2 factor
Estimate B1 factor
B1
B2
Maximum of B1 and B2 as B factor
Credits for the safety measures Quantification
of A
Quantification of SWeHI
All chemicals units checked?
No
Yes
Stop
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Quantification of B1 (fire explosion hazards)

• Energy factors, Fs
• Chemical Energy
• F1 0.1M (Hc)/K
• Physical Energy
• F2 1.304 10-3PPV
• F3 1.010-31/(T273)(PP-VP)2V

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B1 quantification continues

• Penalties for various parameters
• Temperature, pn1
• Pressure, pn2
• Location with respect to others, pn3
• Capacity of the unit, pn4
• Chemicals characteristics, pn5
• Degree of congestion, pn6
• External factor such as earthquake, pn7
• Vulnerability of the site, pn8

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B1 quantification continues
Impact of pressure

• if( VP gt AP )
• if( PP gt VP )
• F F2 F3
• pn2 f(operating pressure)
• else
• F F2
• pn2 f(operating pressure)
• else
• F F3
• pn2 f(operating pressure)
• f(operating pressure) a1 b1.P c1.P2 NF/NRgt2
• a2 b2.P c2.P2 NF/NRlt2

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B1 quantification continues
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Quantification of B2 (toxic hazard)

• B2 is quantified using one core G factor and
  seven penalties
• G Sm
• S is dependent on release condition, and
• m is release rate or mass released

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B2 quantification continues

• Seven penalties are
• Operating temperature, pnr1
• Operating pressure, pnr2
• Vapor density, pnr3
• Chemical characteristics, pnr4
• Population density of the area, pnr5
• Site characteristics, pnr6 and pnr7

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B2 quantification continues
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Quantification of A

• A incorporates the quantification of the various
  control measures
• A is classified in two groups
• Measures to control the damage potential
• Measures to reduce the frequency of occurrence

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Ranking of Hazard
SWeHI Maximum (B1 or B2)/A
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Start

• Hazard identification
• SWeHI

Probabilistic hazard assessment-ASM
Quantitative hazard assessment- MCAA

• Accident scenario development
• MCAS

Fault tree development
Fault tree for the envisaged scenario

• Consequences analysis
• MAXCRED

• Fault tree analysis
• PROFAT

Apply safety measures and re-evaluate risk
Risk estimation
Whether risk is in acceptance?
Suggest safety measures to control risk
No
Yes
End
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Maximum credible accident analysis (MCAA)

• Accident scenario forecasting
• Maximum credible accident scenario (MCAS)
• Damage estimation for envisaged accident scenario
• MAXCRED software

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Maximum credible accident scenario

• The credible accident is defined as the accident
  that is within the realm of possibility (i.e.,
  probability higher than 1e-06 /yr) and has a
  propensity to cause significant damage (at least
  one fatality).

Khan F.I., Chemical Engineering Progress
(AIChE, USA), November, 55-67, 2001
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Take one unit
Develop all plausible accident scenarios
Consider one accident scenario
Toxic and/or corrosive
Is the chemical flammable /or toxic?
Flammable
Calculate factor A
Calculate factor BB
Calculate factor B
Calculate factor CC
Calculate factor C
Calculate credibility factor L1
Calculate credibility factor L2
Calculate total credibility factor L
Classify credibility of the scenario
No
Is it credible?
Yes
List the scenario
Are all units over?
No
Yes
Short list the most credible accident scenarios
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Delineation of maximum credible accident scenarios
0.0

• Credibility of accident scenario is delineated
  using
• L1 (fire and explosion)
• L2 (toxic release)
• L (L12 L22)1/2 for both type of events

Uncertainty zone
0.2
Credibility zone
0.5
Maximum credibility zone
1.0
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Damage estimation- MAXCRED

• MAXCRED enables simulation of accidents and
  estimation of their damage potential

Khan, F.I., and Abbasi, S.A., Environment
Modelling and Software, 14, 11-25, 1999
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Models in MAXCRED

• Fire
• Pool fire
• Flash fire
• Fire ball
• Jet fire
• Toxic release
• Heavy gases
• Light gases
• Domino effect model

• Explosion
• Confined vapor cloud explosion
• Boiling liquid expanding vapor cloud explosion
• Vapor cloud explosion

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Start

• Hazard identification
• SWeHI

Probabilistic hazard assessment-ASM
Quantitative hazard assessment- MCAA

• Accident scenario development
• MCAS

Fault tree development
Fault tree for the envisaged scenario

• Consequences analysis
• MAXCRED

• Fault tree analysis
• PROFAT

Apply safety measures and re-evaluate risk
Risk estimation
Whether risk is in acceptance?
Suggest safety measures to control risk
No
Yes
End
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Analytical simulation method (ASM)

• Main steps
• Fault tree development
• Boolean matrix creation
• Finding of minimum cutsets and optimization
• Probability analysis
• Improvement index estimation

Khan, F.I., and Abbasi, S.A., J of Hazardous
Materials, 75(1), 1-27, 2000
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Start
Represent an undesired event in terms of fault
tree
Transform fault tree into boolean matrix
Solve boolean matrix for minimum cutsets
Optimization of cutsets
Optimization criteria
No
Is optimization over?
Transformation of static probability to fuzzy
probability set
Yes
Probabilistic analysis
Probabilities
Improvement index calculation
ASM Procedure
Stop
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PROFAT

• PROFAT is the software developed based on ASM
• It is coded in C

Khan, F.I., and Abbasi, S.A., Process Safety
Progress (AIChE, USA), 18(1), 1999
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PROFAT modules

• Data
• Minimum cutsets analysis
• Probability analysis
• Improvement factor analysis
• General-purpose module

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Start

• Hazard identification
• SWeHI

Probabilistic hazard assessment-ASM
Quantitative hazard assessment- MCAA

• Accident scenario development
• MCAS

Fault tree development
Fault tree for the envisaged scenario

• Consequences analysis
• MAXCRED

• Fault tree analysis
• PROFAT

Apply safety measures and re-evaluate risk
Risk estimation
Whether risk is in acceptance?
Suggest safety measures to control risk
No
Yes
End
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Risk estimation

• Risk damage potential probability of
  occurrence
• Risk representation
• F-N Curve
• Iso-risk contours

Risk contours over site layout
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Start

• Hazard identification
• SWeHI

Probabilistic hazard assessment-ASM
Quantitative hazard assessment- MCAA

• Accident scenario development
• MCAS

Fault tree development
Fault tree for the envisaged scenario

• Consequences analysis
• MAXCRED

• Fault tree analysis
• PROFAT

Apply safety measures and re-evaluate risk
Risk estimation
Whether risk is in acceptance?
Suggest safety measures to control risk
No
Yes
End
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Safety measures design

• Design measures to control the damage
• Fire resistance barrier,
• Blast resistance barrier, etc.
• Design measures to reduce probability of
  occurrence
• Automatic shut down system,
• Safety relief valve, etc.

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Re-evaluation of Risk

• Modify the fault tree
• Redo the fault tree analysis
• Re-estimate the risk
• Compare risk against acceptable criteria
• Units for which risk could not be brought to
  acceptable level, develop
• Disaster management plan
• Emergency resource plan

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Summary of SCAP

• Hazard identification- SWeHI,
• Hazard quantification-MCAA
• Maximum credible accident scenario
• MAXCRED
• Probabilistic hazard assessment
• Analytical Simulation Method
• PROFAT
• Risk estimation
• Safety measure design
• Risk re-evaluation

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Application of SCAP

• Process facility on a fixed Offshore platform

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Problem Statement

• To design the safety measure for process units of
  a fixed offshore platform
• The platform is located in east coast region of
  Canada (Atlantic Canada), Newfoundland shelf,
  Canada

Khan, F.I., Sadiq, R. and Husain, T., J. Of
Hazardous Materials , A94, 2002,1-36
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Process facilities on offshore platform
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Hazard identification Results
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Maximum credible accident scenario

• Condensate separator
• Formation of vapor cloud due to release of
  flammable gas (wet natural gas) from the unit
  which on ignition causes vapor cloud explosion,
  unreleased chemical in unit burn as Pool Fire
• Compressor unit
• Continuous release of flammable gas (wet natural
  gas) from compressor on ignition cause a jet
  fire

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Damage estimation MAXCRED results for condensate
separator
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Damage estimation MAXCRED results for compressor
__________________________________________________
___________ Parameters
Values _________________________________
____________________________   Fire Jet Fire
Flame length (m) 5.45
Burning rate (kg/s) 10.0 Radiation heat
flux (kJ/m2)
1493     Damage Radii (DR) due to thermal load
  DR for 100 fatality/damage
(m) 24 DR for 50 fatality/damage
(m) 35 DR for 100 third degree of
burn (m) 44 DR for 50 third degree
of burn (m) 57   ___________________
__________________________________________
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Fault tree for a VCE followed by fire in
condensate separator unit
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Fault tree for a jet fire in compressor unit
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Results of ASM

• Condensate separator unit
• The occurrence probability of the envisaged
  accident is 9.474E-04 per year
• Events 18 and 20 (release from connecting pipe
  and ignition due to external energy source) has
  maximum (about 17 each) contribution to the
  probability of the eventual accident
• High pressure in upstream pipeline, ignition due
  to electric spark, release from connective
  vessel, and ignition due to external fire are
  other important events that are making
  significant contribution to this accident

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Results of ASM

• Compressor unit
• The occurrence probability of the envisaged
  accident is 1.364E-02 per year
• Events, external fire causing unit to fail and
  release of chemical and ignition due to of
  external energy sources, have maximum
  contribution (about 47) to the probability of
  the eventual accident
• Ignition due to electric spark, release from
  pipeline, and leak from casing and seal of
  compressor are other important events that are
  making significant contribution to this accident

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FN curve for condensate separator
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Design of safety measures

• Separator and compressor unit
• Flame arrestor
• Cooling system
• Flammable gas detector
• Inert gas purging system
• Preventive maintenance of pumps, pipelines and
  compressor
• Installation of blast barriers

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Occurrence probability reduced from 9.474 E-04 to
1.555E-08 /yr, individual risk from 1.4E-02 to
2.3E-06
Fault tree for condensate separator after
implementing control measures
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Occurrence probability reduced from 1.364E-02 to
1.311E-06 /yr, individual risk from 1.24E-01 to
1.21E-05
Fault tree for compressor after implementing
control measures
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FN curve for condensate separator
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Comparison of individual risk with ALARP criteria
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Thanks
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(No Transcript)
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Why we require safety evaluation

• To ensure

• Safety of equipment, personnel, and environment

• Smooth and continuous operation

• Profitable business