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Hazard analysis of a chemical plant

Hazard analysis of a chemical plant. I risk definition. Hazard: * P as a frequency; * Physical conditions (meteorological, geomorphological). Magnitude: * exposure; * Decrease at increasing distance from the plant; * “decreses” at lower P values. II risk definition. Hazard:

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Hazard analysis of a chemical plant

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  1. Hazard analysis of a chemical plant

  2. I risk definition Hazard: * P as a frequency; * Physical conditions (meteorological, geomorphological) Magnitude: * exposure; * Decrease at increasing distance from the plant; * “decreses” at lower P values

  3. II risk definition Hazard: * P in bayesian sense; * Physical conditions (meteorological, geomorphological) Vulnerability: * exposure; * Vulnerability of urban functions, population (ages), public services…

  4. Difference between PRA and scenario PRA: what is the probability of a given event in a given time B. Scenario: given an event one studies its effects

  5. Hazard analysis: - probability; • Type of failures in the plant - Chain of failures

  6. Hazard assessment A. Inside the plant How a failure may occurr and which one and how it may propagate in the system up to a top event? B.    Outside the plant How the effects of a top event may involve external areas, the outside?

  7. Hazard assessmentA. Inside the plant Plant analysis Assign a probability to each event The safety manager has to: - strive to reduce accidents probability - improve safety procedures - develop and test internal emergency plan

  8. Hazard analsyis inside the plantMethodological aspects 1. Plant analysis: methods What…if, FMEA, Hazop 2. Synthetize of a failure tree 3. Assign a probability (likelihood) estimate to each elementary event 4. Select the most significant scenarios 

  9. Metodo di Dow e Mond: - Logical units of a plant; - penality: damage and areas estimate; - compensations: probability and damage Compensations * Countermeasures and redundancies; * Ways to isolate subst.; * Protection against fire Penalty * Dangerous substance * Dangerous processes

  10. Chemical hazardFrom the inside to the outside: methodological aspects Selection of scenarios that may involve the outside 2. Estimation of probabilities associated to each top event (scenarios) 3. Identify external areas that may be reached by accident’s effects

  11. Chemical hazard analysisA. Inside the plant: problems 1. High reliability theory versus Normal accidents theory (Perrow; il fattore umano) 2. Intrinsic limits of scenarios: - of imagination - new technologies - under-reporting of near missed accidents 3. Limits of estimation of probabilities

  12. Chemical hazard analysis A. Inside the plant: conclusion 1. A series of accidents scenarios Probability associated to each scenario expressed in terms of events/year, events/cycles of process At the end: - decision of preventative measures; - implementation of redundancies, alarms,  emergency devices

  13. Chemical Hazard assessment B. Outside the plant • The first step requires to answer the question of how an accident may propagate outside the plant’s fences: • Fire, thermal radiation, release of heat • Explosion, release of energy • Toxic release (cloud) Within which area?

  14. Chemical Hazard assessment B. Outside the plant 2. In what conditions the external effects may be worsened/mitigated? • Meteorological conditions (winds, atmospheric stability) • Geomorphological conditions, settlement pattern, etc.

  15. Severe accidednts assessment: Damage scenario Hazard * A top event is selected * Context conditions, like weather, geomorphology… * Time of impact Vulnerability and exposure * Human exposure * Distance from the plant * Population and environmental vulnerability

  16. Up to where consequences of an accident may arrive? Continuous release of liquified natural gas, experiments by Maplin Sands, 1982

  17. Continuous release of liquified refrigerated propane, experiments by Maplin Sands, 1982

  18. Sudden release of liquified refrigerated propane, experiments by Maplin Sands, 1982

  19. Damage due to thermal radiation

  20. Damage due to thermal radiation and explosure: thresholds Accident lethal First lethal effects Permanent health effects Temporaryhealth effects Damage to structues fire Small bottles Spheres tanks Fireball radius

  21. Damage due to structures severe repairable repairable Broken windows 20% windows

  22. Toxicity thresholds Inhalation provokes the death of 50% of exposed subjects in a given time Minimal concentration proved to have lethal effects on subjects exposed for a given time Ratio between weight and swallen quantity that provokes the death of 50% of exposed subjects Concentration of a substance that provokes severe effects after 30 min exposure without protection (immediately dangerous to life and healt

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