Risk Assessment of Extreme Events 2 I Introduction

Risk Assessment of Extreme Events 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 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 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 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) 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 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) 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 will happen? ” – “If it does happen, what are the consequences? ” • Several integrated risk assessment/risk management frameworks have been proposed 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 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 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 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 15

III. A Health Risk Assessment (cont. ) • Dose/response relationships (toxicity assessment): – Dose/response models – Empirical relationships between levels of exposure and effects 16

III. A Health Risk Assessment (cont. ) • Risk characterization or calculation: – Risk estimate – Characterization of uncertainties, assumptions, and data quality 17

IIIB Engineering Risk Assessment • Hazard identification • Assessment of accident occurrence frequencies • Consequence analysis • Risk characterization • Uncertainty analysis 18

III. B Engineering Risk Assessment (cont. ) • Hazard identification: – System familiarization – Hazard and operability studies – Failure modes and effects analysis 19

III. B Engineering Risk Assessment (cont. ) • Assessment of accident occurrence frequencies: 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 21

III. B Engineering Risk Assessment (cont. ) • Risk characterization: – Results presented graphically – Probability distribution, complementary cumulative 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 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 24

IV. Understanding Uncertainty • Sources of uncertainty: – – – – Statistical variation Systematic error Subjective judgment Linguistic imprecision Variability Inherent randomness or unpredictability Disagreement Approximation 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 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 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 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 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 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 DAAD 19 -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 31