1. Columbia-Wharton/Penn Roundtable1 Risk Assessment of Extreme Events Rae Zimmerman (New York University) Vicki M. Bier (University of Wisconsin-Madison)

2. Columbia-Wharton/Penn Roundtable2 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

3. Columbia-Wharton/Penn Roundtable3 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

4. Columbia-Wharton/Penn Roundtable4 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

5. Columbia-Wharton/Penn Roundtable5 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)

6. Columbia-Wharton/Penn Roundtable6 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

7. Columbia-Wharton/Penn Roundtable7 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)

8. Columbia-Wharton/Penn Roundtable8 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

9. Columbia-Wharton/Penn Roundtable9 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

10. Columbia-Wharton/Penn Roundtable10 III.A Health Risk Assessment Hazard identification Risk estimation: –Exposure assessment –Dose/response relationships (toxicity assessment) –Risk characterization or risk calculation

11. Columbia-Wharton/Penn Roundtable11 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

12. Columbia-Wharton/Penn Roundtable12 III.A Health Risk Assessment (cont.) Exposure assessment: –Sources, pathways, and sinks (or receptors) –Health effects assessment

13. Columbia-Wharton/Penn Roundtable13 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

14. Columbia-Wharton/Penn Roundtable14 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

15. Columbia-Wharton/Penn Roundtable15 III.A Health Risk Assessment (cont.) Dose/response relationships (toxicity assessment): –Dose/response models –Empirical relationships between levels of exposure and effects

16. Columbia-Wharton/Penn Roundtable16 III.A Health Risk Assessment (cont.) Risk characterization or calculation: –Risk estimate –Characterization of uncertainties, assumptions, and data quality

17. Columbia-Wharton/Penn Roundtable17 IIIB Engineering Risk Assessment Hazard identification Assessment of accident occurrence frequencies Consequence analysis Risk characterization Uncertainty analysis

18. Columbia-Wharton/Penn Roundtable18 III.B Engineering Risk Assessment (cont.) Hazard identification: –System familiarization –Hazard and operability studies –Failure modes and effects analysis

19. Columbia-Wharton/Penn Roundtable19 III.B Engineering Risk Assessment (cont.) Assessment of accident occurrence frequencies:

20. Columbia-Wharton/Penn Roundtable20 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

21. Columbia-Wharton/Penn Roundtable21 III.B Engineering Risk Assessment (cont.) Risk characterization: –Results presented graphically –Probability distribution, complementary cumulative

22. Columbia-Wharton/Penn Roundtable22 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

23. Columbia-Wharton/Penn Roundtable23 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

24. Columbia-Wharton/Penn Roundtable24 IV. Understanding Uncertainty Sources of uncertainty: –Statistical variation –Systematic error –Subjective judgment –Linguistic imprecision –Variability –Inherent randomness or unpredictability –Disagreement –Approximation

25. Columbia-Wharton/Penn Roundtable25 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

26. Columbia-Wharton/Penn Roundtable26 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

27. Columbia-Wharton/Penn Roundtable27 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

28. Columbia-Wharton/Penn Roundtable28 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

29. Columbia-Wharton/Penn Roundtable29 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

30. Columbia-Wharton/Penn Roundtable30 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