Overview of Risk Assessment Principles and Methodologies

1
Overview of Risk Assessment Principles and
Methodologies
2
Risk or Hazard?

• Hazard is
• An intrinsic property of
• a chemical substance
• a given plant
• certain phenomenon,
• that can have an adverse effect on the human life
  and health, on the environment or on anything
  else you consider important.

3
Risk or Hazard?

• Risk is
• the likelihood of a specific effect occurring
  within a specified period or in specified
  circumstances /Seveso II Directive/

4
Risk or Hazard?

• Risk is
• a two-dimensional indicator, which gives the
  probability of an adverse effect to occur and the
  consequences it may have on the human life and
  health, on the environment or on anything else
  you consider important.

5
Why Risk Assessment in Seveso

• Important element of Safety Report
• Often included in SMS
• Provides input to
• Land-Use Planning
• Emergency Plans
• Information to the public

6
Purpose

• To ensure that the level of risk on which the
  population is exposed is not high (is
  tolerable)
• To identify weak points and to contribute to the
  rational management of risk
• To evaluate risk reduction measures

7
Purpose

• To compare establishments and/or other hazardous
  activities in order to decide which ones are the
  most hazardous (and therefore deserve more
  attention/higher priority)
• To help better understanding the risk

8
Risk Assessment
FREQUENCY ASSESSMENT
HAZARD IDENTIFICATION
OVERALL RISK ASSESSMENT
CONSEQUENCE ASSESSMENT
9
General Risk Assessment Principles

• 5 Steps Practical approach
• Identify Hazards
• Identify Targets
• Evaluate the Risks and the Precautions
• Record Significant Findings
• Review and Revise

10
General Risk Assessment Principles

• HAZOP
• What if Approach
• Primary Keywords Aspect of Design, Process
  Condition, Parameter /Flow/
• Secondary Keywords Combined with Primary
  Keywords give Deviation /No/
• Table Format

11
General Risk Assessment Principles

• HAZOP

12
Risk Assessment Methods

• Index Methods (DOW, MOND, , SPIRS)
• Rapid Ranking/Approximation Method (IAEA)
• Qualitative
• Deterministic Approach
• Consequence-based
• Risk-based (Probabilistic or Full QRA)

13
Risk Screening Methods

• Purpose
• Screening of Various Risk Sources (e.g. Hazardous
  Activities)
• Identification of Points Deserving a Further
  Detailed Evaluation
• Getting a Broad Estimation of the Overall Level
  of Risk (Whether it is Generally Acceptable or
  Not)
• Prioritization of Actions / Interventions

14
Risk Screening methods

• Characteristics
• quick-and-dirty
• based on simplified calculations
• small requirements in data (may further need to
  be completed)
• outcome always in a relative context, not absolute

15
Risk Screening Methods

• Two Categories
• Development of an Index
• Rough Estimation of a Physical Magnitude
  Characterizing the Risk (e.g. Risk, Extent of
  Consequences, Maximum Distance of Effect)

16
Indexed Methods

• Strengths
• Simplicity in Definition And in Application
• Weaknesses
• Arbitrary Definition of the Measurement Scales of
  the Parameters
• Arbitrary Definition of the Weights (Relative
  Importance)
• Validation
• Difficult Interpretation
• Difficulty in Cost/Benefit Considerations

17
Indexed Methods

• Principle
• Define an Index, N, for which a Higher Value
  Corresponds to Higher Level of Risk (More
  Hazardous Activity)
• Steps
• Determine Most Important Parameters
• Determine Measurement Scales for All Selected
  Parameters
• Define Aggregation Rule(s) of The Parameters into
  the Index
• Define Relevant Weights

18
DOW Index

• Purpose
• Screening of the Various Units within an
  Establishment (for Prioritization Reasons)
• Rough Estimation of the Probable Property Damage

19
DOW Index

• Principles
• Only Fire and Explosion Hazards
• Depends on the Process (Unit Hazard Factor)
• Depends on the Characteristics of the Substances
  (Material Factor)
• Takes into Consideration Safety Systems (Credit
  Factors)
• Provides a Hazard Index (FE Index) and an
  Estimation Of The Property Damage (Percentage of
  the Unit Likely to be Damaged)

20
DOW Index

• Other Indices
• MOND Index (ICI)
• Italian Indexed Method (Metodo Indicizzato -
  ISPESL)
• Chemical Exposure Index (CEI)

21
SPIRS Hazard Index

• Based on the Swedish Environmental Accident Index
  (EAI)
• Depends on the Quantity of the Substance
• Acute Toxicity to Water Living Organisms
• Consistency or Viscosity/Physical State of the
  Substance
• Solubility in Water
• Vol Volatility
• BA Bioaccumulation
• BD Biodegradation
• Hi Tox Quant (Con Sol/Vol Bd Ba)

22
Approximation Methods

• Principle
• Calculate in an Approximate Way a Physical
  Magnitude Characterizing the Risk (e.g. Risk,
  Extent of Consequences, Maximum Effect Distance)
• Steps
• Classification Activities Type and Inventories
• Identification and Analysis of Typical Scenarios
  for each Category
• Calculation of the Physical Magnitude of Interest
  for each Scenario

23
Approximation Methods

• Strengths
• Direct Assessment of the Physical Magnitude of
  Interest Characterizing the Risk
• Easy Interpretation / Communication to the Public
• Easy Use in Cost/Benefit Considerations
• Easy Verification/Validation
• Weaknesses
• More Background Work is Required (in the
  Development of the Methods)

24
Rapid Risk Assessment Method (IAEA-1996)

• Purpose
• Rough assessment of the typical consequences of
  major accidents related to an installation or a
  hazardous activity (in terms of fatalities) and
  the relevant frequency.
• Acceptability / prioritization is considered
  either in terms of frequency, or in terms of
  consequences, or both

F
C

• Background
• Classification and clustering of types of
  activities and inventories
• Consequence assessment of typical scenarios for
  each category
• Average frequencies for each scenario
• Validation / acceptability of the method

25
IAEA RRA Method - Structure
QUANTITY

• CATEGORY OF EFFECT
• EFFECT DISTANCE
• EFFECT AREA

REFERENCE NUMBER
SUBSTANCE
FATALITIES
TYPE OF ACTIVITY

• POPULATION DENSITY
• POPULATED AREA
• EFFECT AREA

RISK
AVERAGE FREQUENCY
FREQUENCY

• CORRECTION FOR
• LOADING/UNLOADING
• SAFETY SYSTEMS
• ORGANIZATIONAL

PROBABILITY OF WIND
26
Petrochemical -- Acrylonitrile
First zone 525 m Pop 3 Second zone 736 m
Pop 35
27
Qualitative evaluation of risks

• For Consequences
• Minor
• Serious
• Very serious
• Major
• Catastrophic

• For Frequency
• Likely
• Possible, but not likely
• Unlikely
• Very unlikely
• Remote

Frequency
Consequences
28
Deterministic approach

• Steps
• Prescribe technical details
• Prescribe procedures
• Check that all prescriptions have been followed
• Advantage clear and easy in application
• Disadvantage
• Cost usually increased
• absolute results (I.e. safe / unsafe)

29
Consequence-based approach

• Method Distances corresponding to certain levels
  of consequences (thresholds), viewed as
  representing the beginning of lethal and of
  irreversible effects. Assessment of consequences
  of a small number of reference accident
  scenarios. Their likelihood is taken into
  consideration only implicitly (in the definition
  of the scenarios).

• Some examples of threshold values for different
  effects
• LC1 and IDLH (or equivalent dose, for shorter
  exposure times), for toxic releases
• the thermal radiation corresponding - for a given
  exposure period - to 3rd and 1st degree burns
  respectively, for thermal effects
• certain overpressure level (e.g. eardrum
  rupture), for explosions

Z2
Z1
30
Risk-based approach

• Method Zones corresponding to certain levels of
  risk (defined as combination of consequences and
  frequencies), deriving from the assessment of
  both the consequences and the likelihood of the
  accident scenarios. The decisions are based on
  the concept of maximum acceptable or
  tolerable risk.

Principle of Equity
Aversion to increased casualties
31
Risk-based approach - Fault Tree
32
Risk-based approach Event Tree
33
Risk-based approach

• 1. Identification of the hazards.
• 2. Summarising the findings of the hazard
  identification study as a set of scenarios to be
  modelled.
• 3. Estimation of the rates and duration of
  releases, and the quantities of material
  involved.
• 4. Estimation of the consequences of each release
  in terms of an area (as defined by an isopleth)
  inside which, for a given weather condition, a
  specified level of harm (toxic load, explosion
  overpressure, thermal radiation flux) will be met
  or exceeded.

34
Risk-based approach

• 5. Consideration of the effects of mitigation
  (for instance by people going away or staying
  indoors).
• 6. Translation of the release isopleth, by way of
  a model of human impact, into a measure of harm
  (e.g. injury or fatality) to the specified
  individual or population.
• 7. Estimation of the frequencies with which
  events (usually releases of hazardous material
  from their containment) are expected to occur.
• 8. Combination of various probabilities and
  frequencies to calculate numerical estimates of
  risk.

35
(No Transcript)
36
Natural Hazards

• Hazard Probability x Intensity (time)

Intensity (e.g. peak discharge, peak ground
acceleration)
Probability (or, Return Period)
37
Risk Assessment for Natural Hazards

• Risk A measure of the expected losses due to
  hazard event of a particular magnitude occurring
  in a given area over a specific time period.
• Vulnerability The extent to which a community,
  structure, service or geographical area is likely
  to be damaged or disrupted by the impact of a
  particular hazard.
• Risk Hazard x Vulnerability
• Probability x Intensity(t) x
  Vulnerability

38
Vulnerability

• Natural Hazard Apparent Vulnerability Indicator
  (NHAVI)
• NHAVI (Disaster affected population rate) x
  (Disaster economic loss rate)
• DAPR (Population affected) / (Population) x
  1000
• DELR (Economic Losses) / GNP x 1000
• NAHV 6.5 0.9167 LOG (DARP x DELR)
• Scale 1-5 Low Vulnerability 5-9
  Medium Vulnerability
• 9-12 High Vulnerability

39
Integrated Risk Assessment

• Integration of Risk
• Between different plants (domino effect)
• Between plants and transportation
• Between natural and technological hazards
  (natech)
• Purpose To understand the relevance of a
  specific technological or natural risk and the
  quality of its assessment and to compare and
  integrate risk figures form different sources.
• Basic steps for Integrated Risk Assessment
• Characterization of Risk Figures
• Qualification of Risk Figures (and RA process)
• Integration of Risk, risk-informed
  decision-making and risk mapping