Accident a specific unplanned event or sequence of

意外事件之定義： Accident a specific unplanned event or sequence of events that has a specific undesirable consequence. Consequence the results of an accident event sequence. In this course, it is 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, AICh. E, New York(1985).

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

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

DEFINITIONS Incident The loss of containment of material or energy (e. g. , a leak of 10 1 b/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 1 b/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 1 b/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 1 b/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, AICh. E, New York (1989)

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

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

風險之定義： 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 potential for an accident. (AICh. E) Risk the likelihood of 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. (AICh. E)

TYPICAL HAZARDS

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

“hazard”, “risk”, “safety” + “analysis”, “assessment”“evalution” = ? Hazard identification = (a) + (b) Hazard Analysis = (a) + (b) + (c) + (d) qualitative Risk Analysis = (a) + (b) + (c) + (d) quantitative (Hazard Assessment) or (Hazard Evaluation) = (a) + (b) + (c) + (d) + (e) + (f) qualitative Risk Assessment = (a) + (b) + (c) + (d) + (e) + (f) quantitative

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.

風險鑑認評估作業流程圖 System Description Hazard Identification Accident Probabilities Estimation Risk Determination Risk Acceptance Yes Operate System Accident Consequences Estimation No Modify System

Results of Hazard Identification and Assessment • identification and description of hazards which could lead to undesirable consequences. • identification 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.

降低風險之具體方法 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.

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)

[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) – Eliminating 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)

MATRIX RELATING HAZARD EVALUATION PROCEDURES TO HAZARD EVALUATION PROCESS STEPS （左上）

MATRIX RELATING HAZARD EVALUATION PROCEDURES TO HAZARD EVALUATION PROCESS STEPS （左下）

MATRIX RELATING HAZARD EVALUATION PROCEDURES TO HAZARD EVALUATION PROCESS STEPS （右上）

MATRIX RELATING HAZARD EVALUATION PROCEDURES TO HAZARD EVALUATION PROCESS STEPS （右下）

“Acceptable” Risk Most treatment of acceptable risk deal primarily with the risk of 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.

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

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

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 Vehicle industry Chemical industry British industry Steel industry Agricultural work Fishing Coal mining Railway shunting Construction work Air crew Professional boxers Jockeys (flat racing) 0. 15 1. 3 3. 5(a) 4 8 10 35 40(b) 45 67 250 7000 50000 (a). This value of the FAR for the chemical industry predates Flixborough. If the Flixborough fataliyies are averaged over 10 years the value becomes 5. (b). This value is now appreciably less. Sources: Sowby (1964), Pochin (1975), Kletz (1971, 1976 d)

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) United States Sources: Sowby (1964), Pochin (1975), Kletz (1971, 1976 d) 5 5

Table 9. 4 Fatal Accident Rates for some non-industrial activities Fatal Accident Rate (FAR) (deaths/108 exposed hours) Staying at home Travelling: by bus by train by car by bicycle by air by moped by motor scooter by motor cycle Canoeing Rock climbing Sources: Sowby (1964), Pochin (1975), Kletz (1971, 1976 d) 3 3 5 57 96 240 260 310 660 1000 4000

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

Table 9. 5 Death rates for some voluntary and involuntary risks (after Kletz, 1976 d) Fatality rate (deaths person per year) Voluntary risk Taking contraceptive pill Playing football Rock climbing Car driving Smoking (20 cigarettes/day) Involuntary risk Meteorite Transport of petrol and chemicals (U. K. ) Aircraft crash (U. K. ) Explosion of pressure vessel (U. S. A. ) Lightning (U. K. ) Flooding of dikes (Netherlands) Release from nuclear power station (at 1 km) (U. K. ) Fire (U. K. ) Run over by road vehicle Leukemia Reference 2 10 -5 4 10 -5 17 10 -5 500 10 -5 Gibson (1976 c) Pochin (1975) Roach (1970) Pochin (1975) 6 10 -11 0. 2 10 -7 0. 5 10 -7 1 10 -7 Wall (1976) — Gibson (1976 c) Wall (1976) Bulloch (1974) Turkenburg (1974) 1 10 -7 150 10 -7 600 10 -7 800 10 -7 — Melinek (BRE 1974 CP 88/74) — Gibson (1976 c)

“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

OSHA Incidence Rate • OSHA Incidence Rate（傷亡 or 疾病） = (意外傷亡或疾病次數)÷ (員 總 時)× 200, 000 • OSHA Incidence Rate ( 作天數損失) = ( 作天數損失)÷ (員 總 時)× 200, 000 • Based on the total working hours of 100 employees in 1 year (2000 hr/year).

INDIVIDUAL RISK OF ACUTE FATALITY BY VARIOUS CAUSES (From WASH 1400) Accident Type Motor Vehicle Falls Fires and Hot Substance Drowning Poison Firearms Machinery (1968) Water Transport Air Travel Falling Objects Electrocution Railway Lightning Tornadoes Hurricanes All Others All Accidents (Table 6. 1) Nuclear Accidents (100 reactors) 1 Based fatalities Total Number for 1969 Approximate Individual Risk Actual Fatality Probability/yr 3 55, 791 17, 827 7, 451 5, 181 4, 156 2, 309 2, 054 1, 743 1, 778 1, 271 1, 148 884 160 911 932 8, 695 3 10 -4 9 10 -5 4 10 -5 3 10 -5 2 10 -5 1 10 -5 9 10 -6 6 10 -6 4 10 -6 5 10 -7 4 10 -5 6 10 -4 3 10 -9* 0 on total U. S. Population, except as noted. 2(1953 -1971 avg. ) 3(1901 -1972 avg. ) *Based on approximately 15 million people located within 20 miles of nuclear power plants. If the entire U. S. Population of about 200 million people were to be used, then the value would be 2 10 -10 # fatalities total number of population exposed to danger