Presentation is loading. Please wait.

Presentation is loading. Please wait.

Risk Assessment: A Conceptual Introduction

Similar presentations

Presentation on theme: "Risk Assessment: A Conceptual Introduction"— Presentation transcript:

1 Risk Assessment: A Conceptual Introduction
Tee L. Guidotti Occupational Health Program University of Alberta

2 Risk Assessment Risk assessment is the systematic evaluation of the likelihood of an adverse effect arising from exposure in a defined population. Risk assessment is “a systematic process for describing and qualifying the risks associated with hazardous substances, action or events.” (Covello)

3 Other Important Terms Hazard Risk Opportunity
the intrinsic potential for harm toxicity, injury, damage, cost specific to an exposure level Risk probability of (adverse) outcome Opportunity likelihood that significant exposure will occur

4 Hazard  Exposure  Opportunity  Population (at Risk)
A Definition of Risk Risk = (H, E, O, P) Hazard  Exposure  Opportunity  Population (at Risk)

5 Risk Analysis, Risk Management
Hazard identification  Risk assessment  Risk evaluation Risk Management Option generation Option evaluation Option selection Implementation and enforcement

6 Types of Risk Assessment
Qualitative knowledge of hazard knowledge of exposure opportunity estimates of exposure magnitude knowledge of exposure-response informed judgement Quantitative quantification of hazard estimates of population at risk exposure assessment known or extrapolated exposure-response estimate of risk

7 Steps in Risk Assessment - 1
Release assessment potential of emission, effluent, contact pathways of exposure subject to change Exposure assessment intensity frequency duration

8 Steps in Risk Assessment - 2
Consequence assessment human health-related outcomes ecological impact psychological impact cost impact Risk estimation probability of adverse effect for individual probability of adverse effect in population

9 Step by Step through Risk Assessment

10 Step 1. Release Assessment - 1
Identification of the characteristics of “risk source” or “risk agent” that may predict failure or release: monitoring (recording past experience) performance (simulation or experiential) testing (systematic trials) incident evaluation (detailed investigation) modeling (e.g. fault trees , failure analysis)

11 Step 1. Release Assessment - 2
Outcomes: probability of failure or exposure event understanding of how this may happen identification of critical faults or failures Problems: analysis is counterintuitive, complicated may miss multifactoral outcomes assumes a perfect understanding of the system

12 Step 2. Exposure Assessment - 1
Essential elements: pathway and route of exposure “fate and disposition”, dilution, degradation distribution, duration and magnitude of exposures at point of contact multiple exposures and multiple sources of exposure susceptible populations

13 Step 2. Exposure Assessment - 2
Methods: Direct measurement environmental measurement personal measurement biological exposure monitoring Indirect measurement biological effect monitoring biomarkers of exposure (narrowly defined) surveys, consumption records

14 Step 2. Exposure Assessment - 3
Indirect Exposure Estimation extrapolation, ecological association categorization (exposure matrices) simulation surrogate measurements modeling surface water groundwater air dispersion

15 Step 3. Consequence Assessment
General framework:

16 Step 3. Consequence Assessment
Identify plausible outcomes associated with exposure levels implied by exposure assessment Consider susceptible populations and atypical responses Consider health effects as: acute, chronic, lethal Interest in subclinical effects growing

17 Step 3. Consequence Assessment
Key information in Consequence Assessment: exposure-response relationships extrapolation from animal studies toxicological exposure-response relationship epidemiologic exposure-response relationship “low-dose” extrapolation problem stochastic effects modeling

18 Step 4. Risk Estimation - 1 Expressions of risk estimates:
most likely, nominal, “best guess” worst case, conservative assumptions range of probabilities Analyses of sensitivity: critical assumptions behaviour of model (e.g. Monte Carlo) multiple models, assess convergence of prediction

19 Step 4. Risk Estimation - 2 Assumptions:
Human (epidemiological) data preferable to extrapolated data from animal studies If animal data must be used, correct for BSA Conservative assumptions; 95% UL Humans considered as sensitive as most sensitive known animal species Linear, non-threshold model is the UL of response

20 Step 4. Risk Estimation - 3 A generic mathematical model:
Correcting for BSA, assume B = slope B = p/d, p = 95% UL frequency, d = dose Exposure assessment derives estimate for d, based on 70 y lifetime Risk = Bd, if set at 10-6, then derive D (allowable) = 106•B per lifetime

21 Some Problems of Risk Assessment
Quantification (conversion to lives, $, P) Comparability Exposure-response relationships at low levels Chronic low-level v. rare catastrophes Uncertainty bands

22 What Determines When a Risk is Acceptable?

23 Acceptability of Risk - 1
Catastrophic potential – Familiarity + Understanding of risk + Scientific uncertainty – Controllability + (may be an illusion!) Voluntariness + Obvious benefit to community +

24 Acceptability of Risk - 2
Impact on children, future generations – Victim identity – (put a face to the number) Dread – Institutional trust + (few institutions trusted) Media attention – History + Equity + (inequity, maldistribution of risk –)

25 Acceptability of Risk - 3
Reversibility + Personal or family stake in outcome – Attributability – (responsible party) Also: Cultural differences in acceptability ± Outrage (Sandeman), distinct from equity – Profundity – (threat to social stability)

26 Utility of Risk Assessment
Facilitates communication Framework for critical review of data, assumptions Allows problem to be disaggregated into component parts Gaps analysis Comparison of policy options Risk comparison

27 Standardization of Risk Assessment
U.S. federal approach EPA NAS/NRC/IOM Interagency Regulatory Liaison Group: EPA, OSHA, CPSC, FDA, FSQS (now defunct) Health Canada, Health Protection Branch European Community World Health Organization

Download ppt "Risk Assessment: A Conceptual Introduction"

Similar presentations

Ads by Google