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PROCESS HAZARDS ANALYSIS

PROCESS HAZARDS ANALYSIS. Process Hazards Analysis. WHAT ? Fire, Explosions, Toxic Releases Consequences , Mechanism, Improvement WHY ? Ensure Safety to the Public and Employees Risk Management WHO ? Performed by process engineers and plant personnel.

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PROCESS HAZARDS ANALYSIS

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  1. PROCESS HAZARDSANALYSIS

  2. Process Hazards Analysis • WHAT ? • Fire, Explosions, Toxic Releases • Consequences , Mechanism, Improvement • WHY ? • Ensure Safety to the Public and Employees • Risk Management • WHO ? • Performed by process engineers and plant personnel

  3. Process Hazards Analysis Report Contents 1. Hazards Identification 2. Hazardous Events & Consequences Analysis 3. Lines of Defense 4. Recommendations

  4. Process Hazards AnalysisPart 1 - Hazard Identification • Properties of Materials • Reactive - Mix wrong proportions, abnormal chemicals, temperature or pressure excursions • Flammable • Explosive • Toxic - humans, ecology • Comparison to Other Materials

  5. Part 2 - Hazard Events & Consequence Analysis • Toxic Release • Toxic Concentrations - Indoor, Downwind • Fire (Radiation) • Explosion (Physical Explosion, Chemical Explosion) • Pressure Wave, Fireball, Missiles Consequence Analysis Spreadsheet

  6. Hazard Identification - Hazardous Events • Loss Of Containment • Checklists • What-if (Brainstorming) Session • Open-ended Manual Valves, Valve Sheared Off • Pump Seal Failures • Heat Exchanger Tube Rupture • Operation at Abnormal Conditions • What-if Session • HAZOP method • FMEA method

  7. Hazard IdentificationConsequence Analysis • Not all hazards require a numerical quantification of the hazard. • Hazards may be evaluated by Qualitative means using engineering judgement. • A 1/8” dia hole in a water line has no off-site consequences • Deinventory of 3000 lb. of methyl isocyanate (chemical in Bhopal Incident)

  8. Hazard IdentificationConsequence Analysis • For Consequences that are not obvious or that are serious enough that more detail is warranted. Use Quantitative techniques. • Step 1. Determine the Release Rate • Step 2. Determine the Effects

  9. Hazard IdentificationConsequence Analysis • Determining The Release Rate • Assume a scenario • Pick a ‘most likely’ scenario - corrosion causes a 1/8” diameter hole in pipe • Pick a ‘worst case’ scenario - pipe is sheared off by forklift • Use standard engineering calculations to determine the release rate.

  10. Hazard IdentificationConsequence Analysis • Standard Flow Equations (orifices) • Liquid Flow from a tank/pipe under press A - area of hole Co - Orifice Coefficient (usually 0.6 for sharp edge hole) r - density gc - gravitational constant P - Pressure differential

  11. Hazard IdentificationConsequence Analysis • Standard Flow Equations (orifices) • Sonic Vapour Flow from a tank/pipe under press g - Cp/ Cv gc - gravitational constant M- molecular weigth Rg - Gas Coef To - temp (abs) Q - mass flow (sonic exit velocity) Co - Discharge Coef A - Area of hole Po - Inlet Pressure (abs)

  12. Hazard IdentificationConsequence Analysis • Flashing Liquids • A liquid operated above it’s boiling point will flash in a release. • Case 1. The fluid path is very short (through the wall of a vessel) and non-equilibrium conditions exist. The liquid does not have time to flash within the hole. Use Liquid Eqt. • Case 2. The fluid path is greater than about 10 cm then flashing occurs. Use a mixed vap/liq density based on the flash, Ptank - Psat for DP and the liquid Eqt.

  13. Hazard Identification - Consequence Analysis • Toxic Releases • Types: • Ground Level, Elevated, Lighter than Air, Heavier than Air, Neutral buoyant, Continuous Release, Puff Release • Consequences: • Health, Environmental, On-site or Off-site • Causes: • (LOSS of CONTAINMENT) - Leakage (vessel failure, pump or pipe failure, flange failure), drain points, splashes

  14. Consequence Analysis • Toxic Releases - Ground Level

  15. Consequence Analysis • Toxic Releases - Heavier Than Air

  16. Consequence Analysis • Modelling Toxic Releases SAFER - Real Time Release Calculations

  17. Consequence Analysis • Gaussian Distribution Models • Assume • distribution is ‘normal’ • Wind Speed • Surface Roughness • Atmospheric Stability • Sampling Period (Momentary Conc’s high for shorter periods of time)

  18. Consequence Analysis- Toxic Releases • Gaussian Model Ground Level Conc. Y X Elevation Conc. Z

  19. Consequence Analysis - Toxic Releases • Gaussian Model Q = Release Rate u = Wind Velocity x = downwind distance y = cross wind distance z = elevation y = Standard Dev in y direction z = Standard Dev in z direction

  20. Consequence Analysis - Toxic Releases • Typical Values for the Standard Deviation Distance Downwind y, m z, m < 300 m 0.0873 x 0.92 0.0736 x 0.84 300- 4000 m 0.0873 x 0.92 0.01771 x 0.69 For E Atmospheric Stability, Complicated Terrain

  21. Consequence Analysis - Toxic Releases • Gaussian Model - Simplifications • Conc is max at the centre of the plume • Worst Case Wind Speed = 1.5 m/s • Substitute yz = 0.0224x2 for x < 500 m andyz = 0.394x1.54x > 500 m (for night time conditions in a urban release) • Empirical correction factor for elevated release Chemical Engineering - Aug 1998

  22. Consequence Analysis - Toxic Releases • Maximum Concentrations • EPRG 2 - Emergency Planning Response Guideline 2 • LOC - Level of Concern • LD 50 - Lethal Dose , 50% of samples • LC 50 - Lethal Concentration , 50% of samples • IDLH - Immediately Dangerous to Life and Health Level • TLV - Threshold Limit Value

  23. Consequence Analysis - Toxic Releases • Maximum Concentrations • EPRG 2 - The concentration below which almost all people could be exposed for one hour without irreversible or other serious health effects or symptoms that would impair their ability to take protective action • Mechanism • Inhalation, Skin Contact, Swallowing

  24. Consequence Analysis - Toxic Releases • Lines of Defense (Mitigation) • Deinventory Systems • Leak Detection (Air Monitors) • Isolation Systems • Water Sprays (Scrubber Systems, Tank Sprays) • Diking • Operating Procedures

  25. Consequence Analysis - Toxic Releases • Bhopal • A Release involving Methyl Isocyanate • Methyl Isocyanate - EPRG 2: 0.5 ppm • >50,000 lbs released over 2 hours • 2500 deaths • Caused by a disgruntled employee who diverted water into a storage tank. • Union Carbide president cited for criminal negligence charges in India.

  26. Consequence Analysis • FIRES • Types: • Pool Fires, Vapour Cloud Fires (flash fire), Jet Fire • Consequences: • Radiant Heat, Sympathetic Ignition • Causes: • (LOSS of CONTAINMENT) - Leakage (vessel failure, pump or pipe failure, flange failure), drain points, Insulation fires, auto decompositon

  27. Fires - Pool Fire

  28. Fires - Vapour Cloud Fire

  29. Fires - Jet Fire

  30. FUEL OXYGEN IGNITION FIRE • Fire Triangle • Flammable Range • LFL, UFL • LEL, UEL • Oxidizer • Ignition Source (they come for free) Flam. Range 0 % VOL 100 % VOL

  31. Acetone Acetylene Carbon Monoxide Cyclohexane Ethylene Methane (Nat Gas) Propane 13 100 74 7.8 36* 15 9.5 Fire - Flammability Limits LEL UEL (% vol) 2.6 2.5 12.5 1.3 2.7 5 2.1 * 100 % at pressures > 7 MPa (7,000 kPa = 1000 psig)

  32. Fire - Ignition • Heat • autoignition temperatures • flash point • Electrical (spark, static, lightning…) • Open Flames (welding, fired heaters, flares) Open Cup

  33. Fire - Surpression EFFECT OF INERT GASES ON FLAMMABILITY LIMITS

  34. Fire - Consequences • Financial Loss • Personnel Loss

  35. FIRE - CONSEQUENCE ANALYSIS • Vapour Cloud Fires - Fire Ball Size • Diameter (meters) = 5.8 Mass(kg)1/3 • Fire Ball Duration • Time(sec) = 0.45 Mass (kg)1/3 • Radiant Heat Damage • heat evolved and radiated, or • surface emissive power, or • flame temperature and emissivity

  36. FIRE - CONSEQUENCES • Radiant Heat Damage (cont’d) • Heat Release Method r x API RP 521 Method; Fr = 0.16 to 0.38, use 0.3

  37. Fire - Consequences Dose Duration Result kJ / m2 sec 838 1.43 mortality of 99% of people 580 10 mortality of 50% of people 125 30 1st degree burns 1.6 1 Continuous Exposure to People Okay 37.5 1 Damage caused to process equipment 30 1 spontaneous ignition of wood 19 1 cable insulation degrades 15 1 Ignition of wood

  38. Fire - Consequences

  39. Fire • Prevention - Lines of Defense • Flame Arresters • Containment • Dilution (below the LEL) • Emergency Isolation • Water, Foam ...

  40. Explosions • Types: • Deflagration versus Detonation • Vapour Cloud Explosions, Physical (vessel), BLEVE, Dust Explosions, Nuclear • Consequences: • Overpressure, Blast Wave • Missiles • Fireball • Causes: • Fire -> Explosion • Vessel Overpressure • Chemical Reaction

  41. Explosions - Physical • Typically a gas filled container catastrophically failing • most likely to fail at 4 x the vessel design pressure (mechanical over design) • higher temperatures (fire exposure, process excursions) can weaken the steel resulting in lower than expected burst pressure

  42. Explosions - Physical • Isentropic expansion of the gas equation Energy Converted to Blast Wave is usually 40 to 80% E - Ideal Energy Release (Joules) Pb - Burst Pressure (Pa) Ps - Surroundings Pressure (Pa) k = Cp/Cv Source: Bodurtha

  43. Explosions - Vapour Cloud • Difference between Fire and Explosion is the occurrence of Overpressure • Conditions Required • Ignition Source • Gas Concentration in Range for Detonation • Oxidizer ? Detonation 0 % VOL 100 % VOL

  44. Explosions • Detonation Ranges & Flammability

  45. Explosions • Damage Calculations • Step 1. Calculate the TNT Equivalent • Step 2. Determine Overpressure at different distances from the explosion center • Step 3. Determine damage from missiles • Step 4. Decide if off-site consequences exist

  46. Explosions • Vapour Cloud Explosion - TNT Equivalent Explosion x Efficiency (2 %) Mass of Fuel x Heat Of Combustion TNT Equivalent = Heat of Combustion of TNT

  47. Explosions • Overpressure at Distances • method of ‘scaled distance’ Source: Bodurtha

  48. Explosions OverpressureDamage psi 0.03 Large glass windows which are already under strain are broken 0.15 Typical pressure for glass failure 0.3 95% probability of no serious damage 0.1 large and small windows are l00% shattered 0.7 Minor damage to house structures 3 Non-reinforced concrete or cinder walls completely shattered 3 Steel frame building distorted and pulled from foundations 4 Rupture of oil storage tanks is complete 10 Probable total destruction of buildings 300 Limit of crater lip 100 Lethality (low) 200 Lethality (high) 30 lung damage (low) 37 lung damage (high) 5 ear drum rupture

  49. Explosion - Consequences

  50. Explosions - Prevention • Avoidance of Flammable Mixtures • fuel rich, fuel lean, oxygen deficient, inert gases • Elimination of Ignition Sources - impossible ? • Avoidance of Runaway Reactions • Avoidance of Excessive Fluid Pressures

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