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close this bookConducting Environmental Impact Assessment in Developing Countries (United Nations University, 1999, 375 p.)
close this folder9. Emerging developments in EIA
close this folder9.4 Environmental risk assessments
View the document9.4.1 What is environmental risk assessment?
Open this folder and view contents9.4.2 Terminology associated with ERA
View the document9.4.3 ERA and the project cycle
View the document9.4.4 ERA builds upon EIA
View the document9.4.5 Basic approach to ERA
View the document9.4.6 Characterization of risk
View the document9.4.7 Risk comparison
View the document9.4.8 Quantitative risk assessments
View the document9.4.9 Risk communication
View the document9.4.10 Risk management
Open this folder and view contents9.4.11 Guidelines for disaster management planning

9.4.6 Characterization of risk

There are two main purposes in performing ERA: the first to learn about the risks and the second to reduce them. The organization of this information is done through characterization of risks. Risk characterization integrates the information from hazard identification, dose-response relationships, and exposure estimates to determine the probability of risk to humans or to the ecosystem. The risk characterization should consist of discussion, analysis, and conclusions that synthesize the results from the hazard and exposure assessment, present a balanced representation of the available data and its relevancy to the health effects of concern, and identify key assumptions and major areas of uncertainity. All this information must be presented in a manner that can easily be interpreted and used by the relevant personnel.

Table 9.9 Characteristics of hazard evaluation procedures

Procedure

Use

Approach

Performed by

Event scenario

Advantages

Limitations

Information/data requirements

Process or system checklists

Compliance with minimal standards; identify areas requiring further evaluation

Answer questions on previously prepared checklist

Engineer with moderate experience

Not identified

Rapid assessments of hazards

Identifies only hazards previously recognized

Detailed checklist

Safety review

Periodic safety or loss control inspections

Checklists, worker interviews, records review, visual inspection

Team with complementary skills and backgrounds

Normally not identified


Primarily for existing facilities

Checklists, detailed facility information

Relative ranking; Dow and Mond hazard indices

Provides relative ranking of hazards and estimates in-plant consequences

Scoring procedure based on credits and penalties for observed conditions

Engineer with moderate experience

Limited identification

Rapid semi-quantitative estimate of relative risks

Primarily for hazards previously recognized

Calculational parameters based on previous accidents

Preliminary hazard analysis

Precursor to subsequent hazard prevention analysis

Early in design stage, identify broad hazard categories and potential initiating events

Engineer with considerable experience

Potential scenarios identified, but not design specific

Early identification of potential hazards

Dependent on experience and knowledge of analyst

Preliminary plant designs

"What if" method

Identification of potential accident scenarios

Formulate possible deviations in operation and project consequence

Team of experts

Scenarios identified

Can provide thorough evaluation of hazards

Highly dependent on skill of analyst

Detailed facility design information

Hazard and operability studies (HAZOP)

Investigations of possible deviations from design intent

Structured meetings of analysis team to review plant design; use of "guide words"

Multi-disciplinary team of experts

Many scenarios identified for consideration through use of guide words

Procedure stimulates identification of all credible scenarios

Time consuming; only qualitative likelihood of scenarios occurring

Detailed plant designs and operating characteristics

Failure modes, effects, and criticality analysis (FMECA)

Identify modes and effects of equipment failure; possible design improvements input to other analyses

Evaluation and ranking of the effect of each failure independent of other failures

Engineer(s) with considerable experience

Cause of failure is not identified

Thorough evaluation of all equipment failures, their probabilities and effects

Does not consider scenarios with multiple failures

Detailed facility design information; probabilities for equipment failure

Fault tree analysis

Evaluation of alternative sequences of failures and consequences

Accident evaluated in "reverse" to identify possible causes; graphical representations

Engineer(s) with considerable experience

Defined in detail

Thorough identification of all event scenarios

Extensive analysis required to identify scenarios of greatest significance

Detailed facility design information; probabilities for failure modes

Event tree analysis

Evaluation of alternative sequences of failures and results

Evaluation of single and combinations of events "forward" to identify results; graphical representations

Engineer(s) with considerable experience

Defined in detail

Thorough identification of all event scenarios

Extensive analysis required to identify scenarios of greatest significance

Detailed facility design information; probabilities for failure modes

Cause-consequence analysis

Evaluation of alternative sequences of failures and consequences

Combines "reverse" and "forward" analyses of fault tree and event tree analyses

Engineer(s) with considerable experience

Defined in detail

Graphical method that can proceed forward to consequences and reverse to causes

Extensive analysis required to identify scenarios of greatest significance

Detailed facility design information; probabilities for failure modes

Human error analysis

Evaluate role of human error as contributing factors in event scenarios

Various techniques; usually interactive with other hazard analysis techniques

Experts in human performance technology

Contributes to defining scenarios, if conducted as part of other analyses

Provides evaluation of often significant role of human error

Difficulty in transferring results to other contexts

Role of human intervention in specific operations; level of training

In HHRA both individual risks and risks to the population should be characterized. In order to characterize risk to the individual, differences in susceptibility and exposure of individuals must be taken into account. The hypothetical maximally exposed individual is frequently of primary concern. There are two possible descriptors of population risks. The first is the probabilistic number of health effect cases estimated in the population of interest over a specified time. The second type is an estimate of the percentage of the population that would receive exposures greater than the reference dose.

In EcoRA, characterization describes risk in terms of assessment end points, discusses the ecological significance of the effects, and summarizes overall confidence in the assessment.

Risk characterization also contains a description and estimate of the uncertainity of the assessment.