Performance based gas detection for hydrocarbon storage

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The design of hydrocarbon gas detection systems using risk analysis methods is drawing a lot of attention because industry experts have come to a consensus that design codes used in traditional gas …

The design of hydrocarbon gas detection systems using risk analysis methods is drawing a lot of attention because industry experts have come to a consensus that design codes used in traditional gas detection system design work are not sufficient for open-door process areas having serious hazards, such as fire, flammable gas and toxic gas. The ISA Technical Report TR 84.00.07 provides guidelines for the design of fire and gas systems in unenclosed process areas in accordance with the principles given in IEC 61511 standards. This paper presents an overview of the design of gas detection systems using risk assessment methods that are described in the ISA technical report. These methods are statistical in nature and are used to assign and verify targets for the performance metrics (detector coverage and safety availability) of gas detection systems. This paper also provides an overview of the performance based safety life cycle of gas detection systems from conceptual design stage to operations and maintenance.

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  • 1. Performance Based Gas Detection for Hydrocarbon Storage Kenexis Copyright 2011 - Kenexis
  • 2. Presenter Introduction • Edward M. Marszal, PE, ISA84 Expert • President, Kenexis • 20 Years Experience • ISA Author “SIL Selection” • ISA Committees - S84, S91, S18, S84 WG7 Fire and Gas • ISA Safety Division Past Director • ISA Fellow • AIChE, NFPA Member • BSChE, Ohio State UniversityISA84 Expert Copyright 2011 - Kenexis
  • 3. „Basis of Safety‟ for FGS• All critical instrumentation / control systems require a „basis of safety‟ • specify adequate equipment selection and design • specify functional testing requirements• For fire and gas systems „basis of safety‟ are developed in two ways: • Prescriptive „Basis of Safety‟, NFPA/EN standards, etc. • Performance Basis / Risk Assessment Copyright 2011 - Kenexis
  • 4. Prescriptive Standards in FGS Design• Well-established guidance for design of FIRE detection and mitigation systems • Provide detailed requirements for basis of safety for most types of fire detection and alarming function• Allow for performance based alternatives to be used (where appropriate)• Generally not specific to chemical processing• Very little guidance on gas detection Copyright 2011 - Kenexis
  • 5. Performance-Based Standards• ISA TR 84.07 Provides guidance for gas detection design in accordance with the principles of ISA84 / IEC61511 • Specify and Verify Performance Targets • Availability (equivalent to SIL) • Detector Coverage • Written specifically for process industry • Not intended as replacement for prescriptive design; intended as supplement Copyright 2011 - Kenexis
  • 6. Performance-Based or Prescriptive…What‟s Better? • A combination of both prescriptive and performance-based methods in best • Many FGS elements are adequately addressed by prescriptive standards • Many FGS elements (although addressed by prescriptive standards) can be better designed using performance- based methods • Some FGS elements typical found in chemical processing facilities are not adequately covered by prescriptive standards Copyright 2011 - Kenexis
  • 7. Fire and Gas Design Lifecycle Copyright 2011 - Kenexis
  • 8. Fire and Gas Design Lifecycle• Consistent with the underlying principles of ISA 84.00.01 and IEC 61511• Does not provide a complete process for FGS design – only intended for application to process areas Copyright 2011 - Kenexis
  • 9. Typical Workflow for FGS Design Identify Requirement for FGS Design Specification Develop FGS Philosophy Procedure Development FGS Zone Definition Construction, Installation, And Commissioning Determine FGS Performance Requirements PSAT Verify Detector Coverage Operation, Maintenance and Testing Verify FGS Availability Management of Change Modify Design (if required) Copyright 2011 - Kenexis
  • 10. Identifying Requirements for FGS Identify Requirement• Recommended from Previous for FGS Design Specification Safety Studies Develop FGS Philosophy • Process Hazards Analysis (PHA) Procedure Development • Layer of Protection Analysis (LOPA) FGS Zone Definition • Quantitative Risk Assessment (QRA) Construction, Installation, And Commissioning• Required by Government Determine FGS Performance Requirements Regulation PSAT• Required by Industry or Verify Detector Coverage Corporate Standards Operation, Maintenance and Testing• Required by Insurance Provider Verify FGS Availability Management of Change Modify Design (if required) QRA / safety case analysis assumes performance for FGS. Performance Based FGS analysis can be used to verify assumed performance. Copyright 2011 - Kenexis
  • 11. FGS Philosophy Development Identify Requirement Input Task Tools for FGS Deliverable Design Specification Develop FGS Philosophy Identify Requirement Procedure Development for FGS FGS Zone Definition Construction, Installation, And Commissioning Determine FGS Risk Tolerance Performance Requirements FGS Philosophy Criteria Develop FGS Philosophy Template and FGS Philosophy PSAT HSE Philosophy checklist And Procedures Verify Detector Coverage Operation, Maintenance and Testing Verify FGS Availability FGS Management of Change FGS Design Basis Define FGS Zones Toolkit – Modify Design (if required) PHA Pro Report Copyright 2011 - Kenexis
  • 12. FGS Philosophy Elements • Standardized Methods for Categorizing FGS Hazards and Risk • Criteria for Hazard Identification • Criteria for Risk Categorization • Requirements for Safety Analysis and Risk Studies • Standardized FGS Design Heuristics • Criteria for FGS Zone Definition and Grading • Criteria for Assigning Performance Targets to FGS Equipment • Criteria for Selecting Appropriate Sensor Technologies • Alarming Requirements • Manual Activation • Detector Voting for Automatic Action Requirements • Criteria for Detector Setpoint Selection Copyright 2011 - Kenexis
  • 13. Procedures Resulting From Philosophy Hazard Identification (HAZID) Zone Definition and Grading Performance Target Selection Performance Target Verification Residual FGS Release Detected? FGS Effectiveness Residual Fire Effectiveness Frequency Early Ignition? ("Detector Coverage") ("PFD") Delayed Ignition? Detected ("PFD") (1/year) Success 9.10E-06 Yes 0.9 0.85 Failure 1.01E-06 Yes 0.1 0.04 No 1.78E-06 0.15 Success 2.18E-04 0.9 Yes Success 7.43E-07 0.85 0.9 Release Yes 2.97E-04 0.85 Failure 8.25E-08 Yes 0.1 0.04 No 1.46E-07 Failure 0.15 0.1 No 2.33E-05 0.96 No Success 1.31E-06 0.96 0.9 Yes 0.85 Failure 1.46E-07 Yes 0.1 0.04 No 2.57E-07 No 0.15 0.15 No 4.11E-05 0.96 Total 2.97E-04 Copyright 2011 - Kenexis
  • 14. Definition of Fire and Gas Zones Input Task Tools Deliverable Risk Tolerance FGS Philosophy Criteria Develop FGS Philosophy Template and FGS Philosophy HSE Philosophy checklist And Procedures PFD P&ID FGS FGS Zone Definition FGS Zone List Plot/Deck Plan Toolkit Cause-and-Effect Determine FGS FGS FGS Design Basis Performance Requirements Toolkit Report Copyright 2011 - Kenexis
  • 15. Why is Zone Definition Important?• Areas in processing plant have differing fire and gas hazards • Building Fire Protection – zones where goal is protection of personnel and assets from general building fire hazards • Processing Area – zones where goal is incipient detection of fire and/or gas releases in processing areas • Process/Non-Process Segregation – zones where goal is segregator of process hazards from non-process areas• Requirement for clear communication of hazards to operations and emergency responders Copyright 2011 - Kenexis
  • 16. FGS Zone Categories• Zones are categorized to facility development of basis of designZone Categories Area Definition ExamplesH Hydrocarbon Possessing Area, General Fire / Flammable Gas, Production Separation, Toxic Gas Hazard Gas Compression,N Non-Hydrocarbon Fire Hazard Combustible Liquid Storage, Lubrication Oil SystemG General Occupancy, No Hydrocarbon Fire Hazard Accommodations Area, Control BuildingE Non-Hydrocarbon Special Equipment Protection Non-classified Electrical EquipmentT Gas Turbine or Engine Enclosures Gas Turbine and Turbine EnclosuresV Combustion Air Intake / Ventilation Air Intakes Combustion Air blower, HVAC Fresh Air Intake Copyright 2011 - Kenexis
  • 17. FGS Zone List• Complete list of FGS Zones, including: • Identifier (tag, name) • Description • Category Copyright 2011 - Kenexis
  • 18. Fire and Gas Performance Targets Input Task Tools Deliverable PFD P&ID FGS FGS Zone Definition FGS Zone List Plot/Deck Plan Toolkit Cause-and-Effect FGS Philosophy Determine FGS FGS FGS Design Basis & Procedure Performance Requirements Toolkit Report Verify Detector Coverage Effigy™ FGS Detector Mapping Report Copyright 2011 - Kenexis
  • 19. Risk Modeling Requirements• Desire a Risk Model that is sensitive to: – Detector Coverage – FGS System Probability of Failure on Demand• Analysis Considerations include: – Hydrocarbon Processing Equipment – Fire and Gas Consequences – Release Likelihood – Level of Human Occupancy of Zone – Ignition Probabilities – Production Value for Process Copyright 2011 - Kenexis
  • 20. Performance Target Determination• Two Common Approaches – Semi-Quantitative (Similar to LOPA) – Quantitative Risk Analysis (QRA) Copyright 2011 - Kenexis
  • 21. FGS Performance Targets • Performance Targets Specify requirements for Risk Reduction: • Fire and Gas Detector Coverage • Geographic Coverage • Scenario Coverage • Equipment Probability of Failure • Safety Availability • Safety Integrity Level (SIL) Copyright 2011 - Kenexis
  • 22. Fully Quantitative Approach • Targets calculated through rigorous modeling of hazards • Consequence characterized by dispersion/consequence modeling • Release likelihood characterized by equipment failure database • Mitigating factors characterized by site specific factors • Calculated risk compared against tolerability criteria • Design criteria are iteratively modified in order to achieve the tolerable risk target • Analysis based on Scenario Coverage and safety availability Copyright 2011 - Kenexis
  • 23. Hazard Scenario Identification • Hazard scenarios should include general release / fire scenarios – Identify all credible release scenarios, including: • Vessels, process piping, flanges, instruments, wellheads, pumps, compressors, heat exchangers, launchers/receivers, risers and pipelines • Identify specific factors effecting release scenario – Hole size, location, orientation, phase, toxicity (H2S), occupancy • Release Scenarios with extremely low likelihood and/or consequence need not be considered • Result should be a detailed list of release scenarios with enough detail to undertake consequence and likelihood analysis • Identify potential incident outcomes: – Jet fire, Flash Fire, ….. Copyright 2011 - Kenexis
  • 24. Likelihood Analysis • Based on Historical Offshore Data: – Offshore Release Statistics, 2001. UK Health & Safety Exec. – PARLOC 2001: The update of Loss of Containment Data for Offshore Pipelines. UK Health & Safety Exec. • Sensitive to hole size distribution • Sensitive to Equipment Type Fully-Quantitative Method Copyright 2011 - Kenexis
  • 25. Individual Scenario Overlay Large Hole Size Medium Hole Size Small Hole Size Copyright 2011 - Kenexis
  • 26. Risk Integration • Join Consequence and Likelihood to generate a list of possible scenario outcomes – Each outcome has an associated level of risk (PLL, Financial Loss) – Event Trees are used to determine risk for each outcome • Event outcomes are integrated to determine risk for a FGS zone or Platform – Risk for FGS zone/platform is compared against Customer tolerable risk criteria • Initially select low detector coverage and progressively increase until tolerable risk achieved. Fully-Quantitative Method Copyright 2011 - Kenexis
  • 27. Unmitigated Geographic Risk Copyright 2011 - Kenexis
  • 28. Risk Integration – Event Tree Residual FGS Release Detected? FGS Effectiveness Residual Fire Effectiveness Frequency Early Ignition? ("Detector Coverage") ("PFD") Delayed Ignition? Detected ("PFD") (1/year) Success 9.10E-06 Yes 0.9 0.85 Failure 1.01E-06 Yes 0.1 0.04 No 1.78E-06 0.15 Success 2.18E-04 0.9 Yes Success 7.43E-07 0.85 0.9 Release Yes 2.97E-04 0.85 Failure 8.25E-08 Yes 0.1 0.04Estimated Risk is Failure No 0.15 1.46E-07 0.1greater than No 0.96 2.33E-05performance No 0.96 Success 0.9 1.31E-06target, adjust Yes 0.85 Failure 1.46E-07 Yes 0.1parameters to 0.04 No 2.57E-07 No 0.15achieve targets 0.15 No 4.11E-05 0.96 Total 2.97E-04 Fully-Quantitative Method Copyright 2011 - Kenexis
  • 29. Mitigated Geographic Risk 22.4% Coverage Copyright 2011 - Kenexis
  • 30. Revised Mitigated Risk 15.4% Coverage Copyright 2011 - Kenexis
  • 31. Semi-Quantitative Approach • Team-Based approach employing calibrated risk assessment tables • Risk factors qualitatively ranked by team • Likelihood • Consequence • Mitigating factors • Selected categories determine the “zone grade” • Zone grade defines geographic coverage and safety availability Grade Level of Risk Detection Coverage FGS Safety Availability A High Risk 0.90 0.95 (High SIL 1 Equivalent) B Medium Risk 0.80 0.90 (SIL 1 Equivalent) C Low Risk 0.60 0.90 (SIL 1 Equivalent) Copyright 2011 - Kenexis
  • 32. Calibration• Parameters and performance target calibrated by full QRA of typical zones• Safety Availability and Geographic Coverage Set Copyright 2011 - Kenexis
  • 33. Extents of Graded Areas • Define extents of area the overall zone that are required to be covered by fire and gas detection • Limits analysis to location where risk is high • Function of process equipment with potential to leak and process conditions • Similar to electrical area classification Grade C Grade B Grade A Copyright 2011 - Kenexis
  • 34. Verifying FGS Detector Coverage Input Task Tools Deliverable FGS Philosophy Determine FGS FGS FGS Design & Procedure Performance Requirements Toolkit Basis Report FGS Philosophy FGS Detector Verify Detector Coverage Effigy™ & Procedure Mapping Report FGS FGS Availability Verify FGS Availability Toolkit Report Copyright 2011 - Kenexis
  • 35. Why Verify Detector Coverage?• Failure of Gas Detection Systems to Function are related to one of two Mechanisms: • Inadequate Coverage - Failure to detect hazard due to inadequate sensor type, number and/or location • Inadequate Availability - Failure of component hardware to function as intended• Proposed detector layout should be assessed to ensure adequate coverage: • The coverage footprint is sufficient to provide the required hazard alarms and control actions • Detectors are appropriately located considering leak sources, wind directions, and other site specific factors The Maginot Line HSE Statistics Indicate that 40% of Major Gas Release in North Sea Offshore Installations are Not Detected by Gas Detection Systems Copyright 2011 - Kenexis
  • 36. Verifying Detector Coverage for Process Areas• Two methods of coverage verification are defined by ISA TR 84.07: • “Detector Geographic Coverage – The fraction of the geometric area (at a given elevation of analysis) of a defined monitored process area that, if a release were to occur in a given geographic location, would be detected by the release detection equipment considering the defined voting arrangement.” • “Detector (Scenario) Coverage – The fraction of the release scenarios that would occur as a result of the loss of containment from items of equipment of a defined and monitored process area that can be detected by release detection equipment considering the frequency and magnitude of the release scenarios and the defined voting arrangement.” Copyright 2011 - Kenexis
  • 37. Gas Detector Mapping Assessment• Detector Performance characterized based on data from FM approval testing• Detector Coverage calculated based on 3- dimensional modeling• Achieved coverage is compared against performance target• Geographic Coverage considers leak sources and “Design Basis Cloud Size" Copyright 2011 - Kenexis
  • 38. Calculating Gas Geographic Coverage Design Basis Cloud Leak Point (Covered) Leak Point (Not Covered) Copyright 2011 - Kenexis
  • 39. Gas Geographic Coverage 15.4% Coverage Copyright 2011 - Kenexis
  • 40. Verifying FGS Availability Input Task Tools Deliverable FGS Detector FGS Detector Verify FGS Availability Effigy™ Locations Mapping Report FGS FGS Availability FGS List Verify FGS Availability Toolkit Report FGS FGS Performance Modify Design (if required) Toolkit Specifications Copyright 2011 - Kenexis
  • 41. Conceptual Design• Purpose – Select equipment appropriate for performance target – Specify how the system operates – specific and general – Basis for detailed design• Result – FGS Requirements Specification Copyright 2011 - Kenexis
  • 42. Parameters Impacting Availability Copyright 2011 - Kenexis
  • 43. Verifying FGS Availability Copyright 2011 - Kenexis
  • 44. FGS Requirements Specification• Defines FGS behavior – Functional specifications – Integrity specifications• Numerous documents, mainly FGS logic solver functional specification – Logic Description (Cause-and-Effect or Logic Diagram) – General Notes Copyright 2011 - Kenexis
  • 45. Detailed Design and Specs Input Task Tools Deliverable Specification Design Specification Detailed Design Templates Procedure Procedure Development Templates – Procedure Word, DB• Loop Sheets• Internal Wiring Diagrams• Cable Schedules• PLC Programs Copyright 2011 - Kenexis
  • 46. Procedure Development Input Task Tools Deliverable Specification Detailed Design Specs Detailed Design Templates Procedure Procedure Development Templates – Procedure Word, DB• Develop procedures for – Operation of FGS (startup, reset, bypass) – Response to detected failures of FGS – Maintenance and testing of FGS Copyright 2011 - Kenexis
  • 47. Construction, Installation andCommissioning Input Task Tools Deliverable Construction, Installation, And Commissioning PSAT• Purchase equipment• Install on site – location and orientation• Load software• Connect wiring Copyright 2011 - Kenexis
  • 48. Pre Start-Up Acceptance Testing Input Task Tools Deliverable Construction, Installation, And Commissioning Checklist Validation Plan PSAT Punchlists Template• Verify that installed equipment and software conform to safety requirements specifications• Review software and hardware• Review all relevant equipment• Generate deviation record (punchlist) Copyright 2011 - Kenexis
  • 49. Operation and Maintenance Input Task Tools Deliverable Operation, Maintenance And Testing Management of Change• Periodic function testing• Respond to overt faults• NOTHING!!!! Copyright 2011 - Kenexis
  • 50. Management of Change Input Task Tools Deliverable Operation, Maintenance And Testing Management of Change• Follow management of change procedures Copyright 2011 - Kenexis
  • 51. Kenexis Copyright 2011 - Kenexis