Definitions

1. Definitions Accident: a specific unplanned event or sequence of events that has a specific undesirable consequence consequence. Consequences: the results of an accident event sequence. It is originally considered to be the fire, explosion, and release of toxic material that results from the accident, but not the health effects, economic loss, etc., which is the ultimate result. Battelle, Guidelines for Hazard Evaluation Procedures, AIChE, New York (1985).

2. EXAMPLES Feyzin, France, 1966 Fixborough, England, 1974 Bhopal, India, 1984

3. TABLE 1-1. ELEMENTS OF ACCIDENTS Hazards Initiating Event/Upsets Intermediate Events Accident (System or Operator Responses to Upsets) Consequences Propagating Ameliorative Significant Machinery and Equipment Process Parameter Safety System Inventories of Malfunctions Deviations Responses a) Flammable Materials a) Pumps, Valves a) Pressure a) Relief Valves b) Combustible Materials b) Instruments, Sensors b) Temperature b) Back-up Utilities Fires c) Unstable Materials c) Flow Rate c) Back-up Components d) Toxic Materials d) Concentration d) Back-up Systems Explosions e) Extremely Hot ore) Phase/State Change Cold Materials Impacts f) Inerting Gases (Methane, Carbon Monoxide) Highly Reactive Containment Failures Containment Failures Mitigation System Dispersion of Responses Toxic a) Reagents a) Pipes a) Pipes a) Vents Materials b) Products b) Vessels b) Vessels b) Dikes c) Intermediate c) Storage Tanks c) Storage Tanks c) Flares Dispersion of Products d) Gaskets d) Gaskets, Bellows, etc. d) Sprinklers Highly d) By-products e) Input/output or Reactive venting Materials

4. Hazards Initiating Event/Upsets Intermediate Events Accident (System or Operator Responses to Upsets) Consequences Propagating Ameliorative Reaction Rates Control Responses Especially Sensitive to Human Errors Material Releases Operator Responses a) Impurities a) Operations a) Combustibles a) Planned b) Process Parameters b) Maintenance b) Explosive Materials b) Ad Hoc c) Testing c) Toxic Materials d) Reactive Materials Loss of Utilities Ignition/Explosion Contingency Operations a) Electricity Operator Errorsa) Alarms b) Water b) Emergency Procedures c) Air a) Omission c) Personnel Safety d) Steam b) Commission d) Evacuations c) Diagnosis/Decision-Making e) Security External Events External Events External Events a) Floods a) Delayed Warning a) Early Detection b) Earthquakes b) Unwarned b) Early Warning c) Electrical Storms d) High Winds e) High Velocity Impacts f) Vandalism Method/Information Errors Method/Information Failure Information Flow a) As Designed a) Amount a) Routing b) As Communicated b) Usefulness b) Methods c) Timeliness c) Timing

5. DEFINITIONS Incident The loss of containment of material or energy (e. g., a leak of 10 1b/sec of ammonia from a connecting pipeline to the ammonia tank, producing a toxic vapor cloud). Incident Outcome The physical manifestation of the incident; for toxic materials, the incident outcome is a toxic release, while for flammable materials, the incident outcome could be a BLEVE (Boiling Liquid Expanding Vapor Explosion), flash fire, unconfined vapor could explosion, etc. (e. g., for a 10 1b/sec leak of ammonia, the incident outcome is a toxic release). Incident Outcome Case The quantitative definition of a single result of an incident outcome through specification of sufficient parameters to allow distinction of this case from all others for the same incident outcome [e. g., a concentration of 3333 ppm (v) of ammonia 2000 ft downwind from a 10 1b/sec ammonia leak is estimated assuming a 1.4 mph wind, and Stability Class D]. Consequence A measure of the expected effects of an incident outcome case (e. g., an ammonia cloud from a 10 1b/sec leak under Stability Class D weather condition, and 1.4 mph wind traveling in a northerly direction will injure 50 people). *CCPS, Guidelines for Chemical Process Quantitative Risk Analysis, AIChE, New York (1989)

6. INCIDENTS INCIDENT OUTCOMES INCIDENT OUTCOME CASES 5 mph Wind, Stability Class A Toxic Vapor 10 mph Wind, Stability Class D Atmospheric Dispersion 15 mph Wind, Stability Class E o o o etc. Jet Fire Tank Full BLEVE of Tank 50% Full HCN Tank o o o etc. After 15 min. Release Unconfined Vapor After 30 min. Release Cloud Explosion After 60 min. Release o o o etc. The relationship between incidents, incident outcomes, and incident outcome cases for a hydrogen cyanide (HCN) release. 100 1b/min Release of HCN from a Tank Vent

7. Definitions Hazard a physical situation with a potential for human injury, damage to property, damage to environment or some combination of these. (IChem E) a characteristic of the system/plant/process that represents a potentialfor an accident. (AIChE) Risk the likelihoodof a specified undesirable event occurring within a specified period or in specified circumstances. (IChem E) a measure of potential economic loss or human injury in terms of the probability of the loss or injury occurring and the magnitude of the loss or injury if it occurs. (AIChE)

8. TYPICAL HAZARDS

9. TASKS OF HAZARD ASSESSMENT Identification of undesired events. Analysis of the mechanisms by which undesired events could occur. Consideration of the extent of any harmful effects. Consideration of the likelihood of the undesired events and the likelihood of specific detrimental outcomes. Likelihood may be expressed as probability or frequency. Judgements about the significance of the identified hazards and estimated risks. Making and implementing decisions or courses of action, including ways of reducing the likelihood or consequences of undesired events.

10. Risk Assessment Procedure System Description Hazard Identification Accident Probabilities Estimation Accident Consequences Estimation Risk Determination No Risk Acceptance Modify System Yes Operate System

11. “hazard”, “risk”, “safety” + “analysis”, “assessment”“evalution” = ? Hazard identification = (1) + (2) Hazard Analysis = (1) + (2) + (3) + (4)  qualitative Risk Analysis = (1) + (2) + (3) + (4)  quantitative (Hazard Assessment) or (Hazard Evaluation) =(1) + (2) + (3) + (4) + (5) + (6)  qualitative Risk Assessment = (1) + (2) + (3) + (4) + (5) + (6)  quantitative

12. Hazard Identification and Assessment Hazard Identification the techniques for finding out what hazards are present in a plant or process. Hazard Assessment the techniques for deciding how far we ought to go in removing the hazards or protecting people from them.

13. Results of Hazard Identification and Assessment • Identification and description of hazards which could lead to undesirable consequences. • Identification and description of the mechanisms leading to the hazardous event, i. e. accident event sequence. • A qualitative estimate of the likelihood and/or consequence of each accident event sequence. • A quantitative estimate of risk, which can be compared with “acceptable risk” to determine whether or not expenditure on particular safety measure is justified. • A relative ranking of the risk of each hazard and accident event sequence. • Some suggested approaches to risk reduction.

14. Possible Actions to Reduce Risk • A change in the physical design and control system. • A change in the operating procedure. • A change in process configuration or conditions. • A change in the process material. • A change in the testing, inspection/calibration and maintenance procedure of key safety items.

15. Classification of Risk Reduction Measures • Those actions which eliminate hazard (substitution) • Those actions which reduce the likelihood of its occurrence to an acceptable level. (attenuation) • Those actions which eliminate or reduce its consequence. (second chance)

16. [Example] Consider a reaction vessel where, in a HAZOP session, it was discovered that if a certain impurity were introduced with one of the raw materials, there would be a sudden evolution of gas and an increase in pressure. • Solution • Eliminating the possibility of gas evolution by changing the raw material responsible for the problem.(substitution) • Lowering the possibility of gas evolution by altering one of the process condition.(attenuation) • Fitting an appropriate pressure relief valve and vent system to protect the plant.(second chance)

17. MATRIX RELATING HAZARD EVALUATION PROCEDURES TO HAZARD EVALUATION PROCESS STEPS(upper left)

18. MATRIX RELATING HAZARD EVALUATION PROCEDURES TO HAZARD EVALUATION PROCESS STEPS(lower left)

19. MATRIX RELATING HAZARD EVALUATION PROCEDURES TO HAZARD EVALUATION PROCESS STEPS (upper right)

20. MATRIX RELATING HAZARD EVALUATION PROCEDURES TO HAZARD EVALUATION PROCESS STEPS (lower right)

21. What is “acceptable” risk?

22. “Acceptable” RiskMost treatment of acceptable risk deal primarily with the riskof death. This may appear somewhat arbitrary. But there is justification for this approach: • Data on fatalities are most possibly recorded and are relatively straightforward. • (number of fatalities)  (number of other injuries) • measures which reduce death from a particular hazard tend to reduce injuries as well.

23. Computation of Risk where, fi = the rate at which the event occurs (event/year) xi = number of fatalities per event i (death/event) Ni = number of peoples exposed to event i (number of exposed peoples/event) Pi = the probability of fatalities among the exposed people (death/exposed people) N = total number of peoples at risk

24. Fatal Accident Frequency Rate (FAFR) * Based on the total working hours of 1000 employees (2000 hr/year and 50 year/person).

25. Table 9.2 Fatal Accident Rates in different industries and jobs in the U.K. Fatal Accident Rate (FAR) (deaths/108 exposed hours) Clothing and footwear industry 0.15 Vehicle industry 1.3 Chemical industry3.5(a) British industry4 Steel industry 8 Agricultural work10 Fishing 35 Coal mining 40(b) Railway shunting 45 Construction work 67 Air crew 250 Professional boxers 7000 Jockeys (flat racing) 50000 (a). This value of the FAR for the chemical industry predates Flixborough. If the Flixborough fatalities are averaged over 10 years the value becomes 5. (b). This value is now appreciably less. Sources: Sowby (1964), Pochin (1975), Kletz (1971,1976d)

26. Table 9.3 Fatal Accident Rates for the chemical industry in different contries Fatal Accident Rate (FAR) (deaths/108 exposed hours) France 8.5 West Germany 5 United Kingdom (before Flixborough) 4 (including Flixborough) 5 United States5 Sources: Sowby (1964), Pochin (1975), Kletz (1971,1976d)

27. Table 9.4 Fatal Accident Rates for some non-industrial activities Fatal Accident Rate (FAR) (deaths/108 exposed hours) Staying at home 3 Travelling: by bus 3 by train 5 by car 57 by bicycle 96 by air 240 by moped 260 by motor scooter 310 by motor cycle 660 Canoeing 1000 Rock climbing4000 Sources: Sowby (1964), Pochin (1975), Kletz (1971,1976d)

28. Maximum Risk to Employees (Kletz, 1986) (U.S.)

29. Fatality Rate per Person per Year

30. Table 9.5 Death rates for some voluntary and involuntary risks (after Kletz, 1976d) Fatality rateReference (deathsper person per year) Voluntary risk Taking contraceptive pill 2  10-5 Gibson (1976c) Playing football 4  10-5 Pochin (1975) Rock climbing 4  10-5 Pochin (1975) Car driving 17  10-5Roach (1970) Smoking (20 cigarettes/day) 500  10-5Pochin (1975) Involuntary risk Meteorite 6  10-11 Wall (1976) Transport of petrol and chemicals (U.K.) 0.2  10-7 — Aircraft crash (U.K.) 0.2  10-7 Gibson (1976c) Explosion of pressure vessel (U.S.A.) 0.5  10-7 Wall (1976) Lightning (U.K.) 1  10-7 Bulloch (1974) Flooding of dikes (Netherlands) 1  10-7 Turkenburg (1974) Release from nuclear power station (at 1 km) (U.K.) 1  10-7 — Fire (U.K.) 150  10-7 Melinek (BRE 1974 CP 88/74) Run over by road vehicle 600  10-7 — Leukemia 800  10-7 Gibson (1976c)

31. “Acceptable” Risk to Public Voluntary: 10-5/person/year Involuntarily: Natural Disaster 10-5/person/year Man-made 10-7/person/year Maximum Risk to Public (Kletz) Averaged over the whole population(average risk) 10-7/person/year For anyone in public(individual risk) 10-5 to 10-6/person/year

32. OSHA Incidence Rate • OSHA Incidence Rate (injury or sickness) • OSHA Incidence Rate (loss of work days) • Based on the total working hours of 100 employees in 1 year (2000 hr/year). = (total number of injuries/sicknesses ) ÷ (total working hours of all employees) × 200,000 = (total number of lost work days)÷ (total working hours of all employees) × 200,000