Risk Assessment of Extreme Events

1. Risk Assessment of Extreme Events Rae Zimmerman (New York University) Vicki M. Bier (University of Wisconsin-Madison) Columbia-Wharton/Penn Roundtable

2. I. Introduction and Scope • Risk assessment is a means to characterize and reduce uncertainty to support our ability to deal with catastrophe • Scope of this paper: • Application of risk assessment to both the built and natural environments under extreme events • Understanding and management of human health, safety, and security Columbia-Wharton/Penn Roundtable

3. I. Introduction and Scope (cont.) • Modern risk assessment for engineering began with Reactor Safety Study (1975): • Applications to engineered systems and infrastructure are common • Applications to chemical risks under dozens of federal environmental statutes: • E.g., drinking water, ambient water quality, and air quality standards • Review and renewal of pesticide applications • Levels of site cleanup under Superfund Columbia-Wharton/Penn Roundtable

4. II. What is Risk Assessment? • Definition of risk assessment: “A systematic approach to organizing and analyzing scientific knowledge and information for potentially hazardous activities or for substances that might pose risks under specified circumstances” National Research Council (NRC), 1994 Columbia-Wharton/Penn Roundtable

5. II.A Definitions of Risk • “Both uncertainty and some kind of loss or damage” (Kaplan and Garrick 1981) • “The potential for realization of unwanted, negative consequences of an event” (Rowe 1976) • “The probability per unit time of the occurrence of a unit cost burden” (Sage and White 1980) • “The likelihood that a vulnerability will be exploited” (NRC 2002) Columbia-Wharton/Penn Roundtable

6. II.A Definitions of Risk (cont.) • Terms to characterize acceptable risk in health and safety legislation: • Adequate • Imminent • Substantial • Reasonable (vs. unreasonable) • Posing grave danger • At a zero level • Significant (vs. de minimus) • An ample or adequate margin of safety Columbia-Wharton/Penn Roundtable

7. II.B Relationship of Risk to Other Concepts • Merriam-Webster’s Collegiate Dictionary 2002: • Hazard (“a source of danger”)   • Catastrophe (“a momentous tragic event”) • Chronic (“long duration or frequent recurrence”) • NRC 2002: Threat (“an adversary”) • Vulnerability (“an error or a weakness”) • Extreme events (low frequency and high severity) • Counter-expected events (believed to be unlikely) • Unexpected events (not even anticipated) • Uncertainty (lack of knowledge) • Variability (differences among a population) Columbia-Wharton/Penn Roundtable

8. II.C Paradigms for Risk Assessment • A form of systems analysis • Answers three questions (Kaplan and Garrick 1981): • “What can go wrong?” • “How likely is it that that will happen?” • “If it does happen, what are the consequences?” • Several integrated risk assessment/risk management frameworks have been proposed Columbia-Wharton/Penn Roundtable

9. II.C Paradigms for Risk Assessment (cont.) • “Deliberation frames analysis and analysis informs deliberation” (Stern and Fineberg 1996): • The combination of these two steps is termed the “analytic-deliberative” process • An iterative process • Deliberation and analysis are viewed as complementary Columbia-Wharton/Penn Roundtable

10. III.A Health Risk Assessment • Hazard identification • Risk estimation: • Exposure assessment • Dose/response relationships (toxicity assessment) • Risk characterization or risk calculation Columbia-Wharton/Penn Roundtable

11. III.A Health Risk Assessment (cont.) • Hazard identification: • Structure activity relationships (structural toxicology) • Case clusters • Epidemiological studies • Experimental chemical tests on lower order organisms (rapid screening) • Animal tests Columbia-Wharton/Penn Roundtable

12. III.A Health Risk Assessment (cont.) • Exposure assessment: • Sources, pathways, and sinks (or receptors) • Health effects assessment Columbia-Wharton/Penn Roundtable

13. III.A Health Risk Assessment (cont.) • Sources, pathways, and sinks (receptors): • Source characterization (substances released, rates of release, temporal variations, location) • Fate and transport • Routes or pathways of exposure from environmental end points to human organisms • Size, type, and sensitivity of population at risk  Columbia-Wharton/Penn Roundtable

14. III.A Health Risk Assessment (cont.) • Health effects assessment: • Dose estimates or intake levels • Absorption by the body • General toxicity of the risk agent in the body (e.g., target organs, types of effects) • State of health of the organism Columbia-Wharton/Penn Roundtable

15. III.A Health Risk Assessment (cont.) • Dose/response relationships (toxicity assessment): • Dose/response models • Empirical relationships between levels of exposure and effects Columbia-Wharton/Penn Roundtable

16. III.A Health Risk Assessment (cont.) • Risk characterization or calculation: • Risk estimate • Characterization of uncertainties, assumptions, and data quality Columbia-Wharton/Penn Roundtable

17. IIIB Engineering Risk Assessment • Hazard identification  • Assessment of accident occurrence frequencies   • Consequence analysis  • Risk characterization • Uncertainty analysis Columbia-Wharton/Penn Roundtable

18. III.B Engineering Risk Assessment (cont.) • Hazard identification: • System familiarization • Hazard and operability studies • Failure modes and effects analysis Columbia-Wharton/Penn Roundtable

19. III.B Engineering Risk Assessment (cont.) • Assessment of accident occurrence frequencies: Columbia-Wharton/Penn Roundtable

20. III.B Engineering Risk Assessment (cont.) • Consequence analysis has two stages: • Migration of hazardous materials from sources to sinks • Consequences of those materials for public health and safety • Relevant consequence measures include: • Structural response of a building • Costs of property damage, loss of use, repair • Amount of hazardous material released • Numbers of fatalities or other health effects Columbia-Wharton/Penn Roundtable

21. III.B Engineering Risk Assessment (cont.) • Risk characterization: • Results presented graphically • Probability distribution, complementary cumulative Columbia-Wharton/Penn Roundtable

22. III.C Spatial Dimensions • Proximity is a key factor in the exposure portion of the risk equation • Proximity can also affect: • Perceived severity of particular scenarios • Conditional failure probabilities Columbia-Wharton/Penn Roundtable

23. III.C Spatial Dimensions • Despite this, risk analyses rarely use sophisticated spatial concepts or models: • Methodology for doing so tends to be ad hoc • Takes little advantage of GIS systems Columbia-Wharton/Penn Roundtable

24. IV. Understanding Uncertainty • Sources of uncertainty: • Statistical variation • Systematic error • Subjective judgment • Linguistic imprecision • Variability • Inherent randomness or unpredictability • Disagreement • Approximation Columbia-Wharton/Penn Roundtable

25. IV. Understanding Uncertainty (cont.) • Uncertainty and variability have different implications for decision-making (NRC 1994): • “Uncertainty forces decision makers to judge how probable it is that risks will be overestimated or underestimated” • “Variability forces them to cope with the certainty that different individuals will be subjected to [different] risks” • Large uncertainty suggests that further research may be desirable Columbia-Wharton/Penn Roundtable

26. V. Human Perceptions, Behavior, and Performance • Evacuation responses in emergencies differ substantially from performance in tests and simulations • Behavioral assumptions underlying many building codes and strategies are flawed • Human behavior is extremely variable: • Healthy versus elderly, ill, or disabled • Familiarity with a particular environment   • Predicting the behavior of the public is a difficult challenge Columbia-Wharton/Penn Roundtable

27. V. Human Perceptions, Behavior, Performance (cont.) • Intentional hazards: • Estimating the likelihood and nature of intentional attacks “is needed for intelligent benefit-cost analysis” (Woo 2002) • Protection from an adversary is different than protection against accidents: • Adversaries can choose to attack targets that have not been hardened • Defensive measures may be less effective if they are known • Optimal strategy depends on attacker behavior Columbia-Wharton/Penn Roundtable

28. VI. World Trade Center Disaster • Unexpected or counter-expected • Past experiences could have helped to identify risk of an attack (Barnett 2001): • “Lots of events…could be interpreted as precursors of the calamity” • “All the elements of the Sept. 11 catastrophe… had historical precedent” • This points out the need for: • Methods of learning from past experience • Vigilance to signs of problems Columbia-Wharton/Penn Roundtable

29. VII. Conclusions • Risk assessment is a vital tool for dealing with extreme events • Capabilities of risk assessment are challenged when we attempt to apply it to extreme and unanticipated events • Need for methodological improvements to more fully incorporate: • Spatial dimensions • Human values, attitudes, beliefs, and behavior • Past experience Columbia-Wharton/Penn Roundtable

30. Acknowledgments • This material is based upon work supported in part by: • The U.S. Army Research Laboratory and the U.S. Army Research Office under grant number DAAD19-01-1-0502 • The National Science Foundation under Cooperative Agreement No. CMS-9728805 • Any opinions, findings, conclusions, or recommendations expressed in this document are those of the authors Columbia-Wharton/Penn Roundtable