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Overview

Process Hazard Analysis and Offsite Consequence Analysis 9th Annual California Unified Program Conference Howard Balentine, CCM, PE ENSR hbalentine@ensr.aecom.com February 14, 2007. Overview. Introduction Process Hazards Analyses (PHA) Offsite Consequence Analysis (OCA) Questions.

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Overview

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  1. Process Hazard Analysis and Offsite Consequence Analysis9th Annual California Unified Program ConferenceHoward Balentine, CCM, PEENSRhbalentine@ensr.aecom.comFebruary 14, 2007

  2. Overview • Introduction • Process Hazards Analyses (PHA) • Offsite Consequence Analysis (OCA) • Questions

  3. Why We Are Here TodayDecember 2, 1984Bhopal, India

  4. Definition of Process • Use, storage, manufacture, handling, and/or on-site movement of a listed substances • A group of vessels used in an activity involving a listed substance including: • Single vessels • Inter-connected vessels • Groups of vessels such that a single event could a release from multiple vessels

  5. PHA Process is Composed of the Following Steps • Identify potential hazard scenarios • Identify the potential consequences • Follow the upstream chain of initiating events • Identify the root cause • Identify mitigation measures in place • Recommend additional mitigation (if any)

  6. Factors Reviewed During the PHA • How Likely is the event to occur? • What is the Consequence if the event happens? • What Systems and Procedures are in place to prevent and/or mitigate the occurrence of the event? • Are there Other Similar Events that would produce a more hazardous condition?

  7. Other Relevant Factors • Previous incidents and near misses • Consequences of failures of engineering and administrative controls • Human factors • External events that could cause a release of the regulated substance

  8. An RMP Level 2 PHA Should Examine the Following: • The critical hazards associated with the process and regulated substances • Opportunities for equipment malfunction or human error that could cause accidental release • Safeguards to control the hazards or prevent equipment malfunction and human error • Any steps used or needed to detect and monitor releases 40CFR 68.50

  9. An RMP Level 3 PHA Should Address: • Hazards of the process • Past accidents / near misses • Engineering and administrative controls • Consequences of a failure of controls • Stationary source siting issues • Human factors • Possible safety and health effects of failure of controls 40CFR 68.67

  10. Steps in Conducting a PHA • Define Study Objectives

  11. Steps in Conducting a PHA • Define Study Objectives • Establish Review Team

  12. Who Should be on the RMP Process Hazards Analysis Team? • Leader / Facilitator • Plant Management Representative • Plant Environmental Manager • Maintenance Manager • Operations Manager • Operator(s) • CUPA/Fire Department Representative • Chemical Supplier Representative • Scribe

  13. Steps in Conducting a PHA • Define Study Objectives • Establish Review Team • Define PHA Methodology

  14. Potential PHA Approaches • What-If • Checklist • What-If/Checklist • HazOp • Failure Mode and Effects Analysis (FMEA) • Fault Tree Analysis • Equivalent Methodology 40CFR 68.67

  15. What-If Approach “What happens if the loading hose coupling disconnects at the truck during unloading?” • Identify the consequences • Pressurized release of chemical • Follow the upstream chain of initiating events • Improper hose connection • Identify the root cause(s) • Operator error • Identify mitigation measure(s) in place and/or needed • Driver pump “Kill” switch • Excess flow valve on truck • Driver checklist • Truck unloading SOP

  16. Guide Words

  17. More than One Guide Word May Be Applicable "The operator starts Flow A when Pressure B is reached” • Guide Words applied to Flow A • No, More, Less, etc. • Guide Words for when Pressure B is reached • Sooner, Later, etc. • Examine the potential hazards produced by all the applicable combinations of deviations

  18. “What Happens in Vessel A if PRESSURE is HIGH?” • Identify the consequence of the deviation • Loss of containment resulting in release of chemical • Follow the upstream chain of initiating events • Uncontrolled exothermic reaction in vessel • Identify the root cause(s) • Loss of heat removal capacity by cooling system • Loss of cooling fluid due to leak in primary coil • Leak due to metal fatigue and corrosion • Primary cause - materials failure • Contributing cause - maintenance failure • Identify mitigation measure(s) in place and/or needed • Automatic shutdown on high temperature warning • Quench drop initiation on high-high temperature warning • Maintenance SOPs

  19. Steps in Conducting a PHA • Define Study Objectives • Establish Review Team • Define PHA Methodology • Assemble needed data

  20. Information Needed for the PHA • Regulated substance(s) information • Quantities, chemical & physical hazards, storage, safety systems • Process Flow Diagram(s) • Piping and Instrument Diagram(s) (P&ID) • Previous PHA documentation • Accident / near miss history

  21. Steps in Conducting a PHA • Define Study Objectives • Establish Review Team • Define PHA Methodology • Assemble needed data • Conduct the PHA

  22. Divide the Process into Functional Units (Nodes) Node 1 Unloading Node 3 Pumps thruSCR Injectors Node 2 Tank

  23. Breakdown each node into individual elements for review • Example for Truck Unloading • Hose connection • Hose integrity • Delivery pump • Wrong substance delivered • Premature truck drive away • …..

  24. Determine the Risk Posed by Each Deviation Risk is Determined by the Severity and Likelihood of an Event

  25. HIGH RISK Events with HIGH CONSEQUENCE and HIGH LIKELIHOOD of occurrence Drunken driving To be avoided at all cost

  26. LOW RISK Events with HIGH CONSEQUENCE and LOW LIKELIHOOD of occurrence Airplane crashing into the facility duringan earthquake Not considered further

  27. Categorize the Results Using a Risk-Severity Matrix

  28. Increasing Severity

  29. Increasing Probability

  30. Keep Notes and Compile the Results

  31. Process Hazard Analysis Questions?

  32. Offsite Consequence Analyses

  33. Components of an Offsite Consequence Analysis • Definition of spill scenarios

  34. Mandatory RMP Release Scenarios • Worst-Case • All levels of RMP • Largest vessel with worst-case meteorology • Extremely conservative • Alternative Scenario • Level II and Level III RMPs • User-defined release • Less conservative meteorological conditions • Typically the most probable release scenario

  35. Toxic Liquid/Gas Worst-Case Scenario • 10-minute release of entire contents of largest single vessel • Liquid release • Liquid pool formation (inhalation) • Liquid/gas release • Vapor cloud formation (inhalation) • Cold liquid/gas release • Dense gas formation (inhalation) • May account for passive mitigation only (containment dike) • Assumes nighttime spill

  36. Flammable Liquid/Gas Worst-Case Scenario • 10-minute release of entire contents of largest single vessel • Gas releases • Vapor cloud explosion (thermal and overpressure) • Liquid releases • Vapor cloud explosion (thermal and overpressure) • Liquid pool fire (thermal) • Boiling Liquid Expanding Vapor Explosion (BLEVE) (thermal and overpressure) • Cold liquid/gas release • Dense gas formation (thermal and overpressure) • May account for passive mitigation only (containment dike if liquid) • Assumes nighttime spill

  37. Toxic / Flammable Liquids and Gases Alternative Release Scenario • More realistic type of release • Facility can define release based on specific operations • May account for active mitigation • Emergency cut-off switches • Deluge systems • Sprinklers • Other • Assumes daytime release

  38. Example Bulk Chemical Release Scenarios (Toxic Release) • Worst Case Release • Release of entire contents of storage tank • Spill contained by containment structure • Nighttime, low wind speed release • Alternative Release • Detached hose during unloading • 3-minute release before pump shutoff • Daytime release

  39. Example Flammable Liquid/Gas Alternative Release Scenarios • Impact hole on pressurized tank producing a horizontal jet - no controls • Jet flame - Thermal • Liquid spills from valve into containment structure and ignites • Pool fire - Thermal • Burst pipe with liquid to gas phase change and adiabatic cooling - automatic shutoff • Vapor cloud explosion - Thermal and blast

  40. Components of an Offsite Consequence Analysis • Definition of spill scenarios • Estimation of emission rate

  41. Factors to Consider in Selection of Emission Model • Form of substance (liquid, gas, solid) • Phase change (if any) • Complexity of release scenario • Inside or outside of buildings • Containment or no containment • Duration of release • Adiabatic cooling • Exothermic reaction

  42. Emission Models • EPA “Risk Management Program Guidance for Offsite Consequence Analysis” • Lookup tables • Equations • EPA RMP*COMP • NOAA ALOHA • Commercial Models (BREEZE-Haz, CHARM, etc) • Engineering computations (i.e., Perry’s Handbook)

  43. ALOHA Emission Rate Estimation

  44. Secondary Containment Effective in Reducing Liquid Pool Emission Rates

  45. Evaporative Emission Rate Tends to Follow the Temperature Curve

  46. Components of an Offsite Consequence Analysis • Definition of spill scenarios • Estimation of emission rate • Computation of offsite consequence

  47. Determine Zone of Impact • Air quality modeling is used to assess the distance of toxic impact • Impact threshold defined in RMP guidance • Toxics - ERPG-2, IDLH, etc • Flammables - 1 PSI overpressure • Other endpoints • Thermal impact for pool fire, fireball - 5 kW/m2 • Distance to LEL for flammable substances

  48. Model Selection is Based on Release Scenario • Dense gas versus neutral buoyancy • Source release characteristics • Evaporating pool and pool fire • Vapor cloud explosion • Jet fire • BLEVE • Phase of substance • Liquid, gas, dense gas, aerosol • Other factors • Integration of emissions and dispersion model • Ease of use

  49. Release Dispersion Modeling Tools • EPA “Risk Management Program Guidance for Offsite Consequence Analysis” (EPA 550-B-99-009) • EPA RMP*COMP Model • NOAA CAMEO • DEGADIS • SLAB • Commercial Models (BREEZE-Haz, CHARM, etc) • EPA SCREEN3, ISCST3, AERMOD

  50. Comparison of Alternative Models

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