unified hazard assessment...–lopa worksheet filtered to only show flagged scenarios –fields...
TRANSCRIPT
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Unified Hazard AssessmentBringing Together HAZOP, LOPA, Hazard Registers and Bowtie in a Unified Data Structure
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Introduction
• PHA was initially “check the box” – minimum compliance and
minimum cost
• Value found in PHA information, expanded to other purposes
– LOPA – for SIS safety integrity levels
– Hazard Registers – tracking and understanding of significant hazard
scenarios
– Bowtie diagrams – Visualization of hazard scenarios
• Maximizing usefulness of data developed during PHA will require
changes in data structure and practices
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Extending PHA to LOPA
• LOPA increases precision for significant hazards
• LOPA increases scrutiny of effectiveness of safeguards
– Separately considers initiating events and safeguards
– Assesses effectiveness of safeguards
• PHA and LOPA should be consistent in terms of consequence
and listed safeguards
• LOPA extends analysis
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Bowties Visualize Hazard Scenarios
• Graphical representation
– Multiple Causes
– Multiple Consequences
• Bowtie “knot” is loss of containment (process industries)
• Shows in a single diagram all causes, consequences, and factors
influencing risk
• Hazard Register entries are simplified LOPA scenarios can be
visualized with Bowtie
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Bowtie Diagram
Inadvertent Closure of Discharge Valve
SIS – Low Flow Shutdown
Pump Discharge Valve Fails Closed
Operator Action Based on LAL
SIS – Low Flow Shutdown
Ignition Control –Probability of Ignition
Toxic Vapor Exposure
Pool Fire
Pump Seal Failure –Leakage of Process
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Problems with Existing PHA Documentation
• Scenarios documented in improper location
– “cause local – consequence global” results in cause-indexing
– Scenario documented where cause occurs
• Subsequent studies generally interested in hazard scenario
• LOPA studies are optimized by consequence indexing
– LOPA – for SIS safety integrity levels
• Everything is documented in the flow deviation
– “Poor Man’s FMEA”
• Multitude of different file formats at a single facility
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Typical PHA – Cause Indexed
Cause 1
Consequence 1.1
Safeguard 1.1.1
Safeguard 1.1.2
Consequence 1.2
Safeguard 1.2.1
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Typical LOPA – Consequence Indexed
Consequence 1
Cause 1.1
IPL 1.1.1
IPL 1.1.2
Cause 1.2 IPL 1.2.1
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Bowties – Hazard Indexed
Hazard 1 (LOC)
Cause 1.1
Preventive Barrier 1.1.1
Preventive Barrier 1.1.2
Consequence 1.1
Mitigative Barrier 1.1.1
Mitigative Barrier 1.1.2
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Unified Hazard Assessment Data Structure - Fields
• Define and standardized all
fields used in hazard
assessment
• Super-set Concept –
Customizable View
• Subject of Research at
P2SAC
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UHA Implementation and Benefits
• PHA (HAZOP)– New key field of hazard scenario must be documented
– Workflow changed to document at hazard scenario, not cause
– Subset of fields optimized for PHA
• LOPA– Each PHA scenario includes flag indicating inclusion in LOPA
– LOPA worksheet filtered to only show flagged scenarios
– Fields displayed expanded to include LOPA specific information, which is expanded upon existing PHA information, not re-created
• Hazard Register– Flagged high risk PHA scenarios – limited fields displayed
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UHA Implementation and Benefits - Bowtie
Inadvertent Closure of Discharge Valve
SIS – Low Flow Shutdown
Pump Discharge Valve Fails Closed
Operator Action Based on LAL
SIS – Low Flow Shutdown
Ignition Control –Probability of Ignition
Toxic Vapor Exposure
Pool Fire
Pump Seal Failure –Leakage of ProcessTag: XV-01
F: 0.1 /yr Tag: LAL-01
PFD: 0.1 Typ: Alm
Tag: UZC-02
PFD:0.01 Typ: SIS
SIL: 2
Tag: UZC-02
PFD:0.01 Typ: SIS
SIL: 2
Tag: XV-01 (OP)
F: 0.001 /yr
Cat S: Moderate
TMEL: 1E-3F: 1E-4
F: 1E-5
F Total: 1.1E-4
F ACT: 1.1E-5
Tag: IC-UZC1
PFD=0.1
Tolerable: No
Tolerable: Yes
Cat S: Severe
TMEL: 1E-4
F ACT: 1.1E-4
Tolerable: No
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UHA – Future Development
• Handling of Mitigative Safeguards
– Mitigative safeguards operate after loss of containment
– In LOPA, referred to as conditional modifiers
– Currently only usable if when successful mitigate consequence to zero
– Many mitigative safeguards leave significant residual consequence
– Mitigative safeguards could include consequence category if successful
– Requires tracking of multiple targets for different consequence
categories
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Effect of Consequence Mitigation
• A tank dike is used as a mitigative barrier
– Successful operation could result in a flash fire with moderate injury• Lower Severity
• Higher Likelihood
– Failed operation could result in a large vapor cloud explosion• Higher Severity
• Lower Likelihood
– BOTH OUTCOMES MUST BE TRACKED
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LIKELIHOOD
SE
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Y -
SA
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TY
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Conclusions
• PHA data desired to be used for other purposes
• Current methods and data structures will not allow it
• Use of internet data structures and communication techniques
will improve usability of PHA data
• Unified Hazard Analysis Data structure will standardize data and
allow use for multiple purposes