Risk Assessment: Risk Assessment: A Conceptual A Conceptual Introduction Introduction Tee L. Guidotti Occupational Health Program University of Alberta
Dec 23, 2015
Risk Assessment:Risk Assessment:A Conceptual A Conceptual IntroductionIntroduction
Tee L. Guidotti
Occupational Health Program
University of Alberta
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)
Other Important Terms
• Hazard– 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
A Definition of Risk
Risk = (H, E, O, P)
Hazard Exposure Opportunity Population (at Risk)
Risk Analysis, Risk Management
• Risk Analysis– Hazard identification – Risk assessment – Risk evaluation
• Risk Management– Option generation
– Option evaluation
– Option selection
– Implementation and enforcement
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
Steps in Risk Assessment - 1
1 Release assessment– potential of emission, effluent, contact– pathways of exposure– subject to change
2 Exposure assessment– intensity– frequency– duration
Steps in Risk Assessment - 2
3 Consequence assessment– human health-related outcomes– ecological impact– psychological impact– cost impact
4 Risk estimation– probability of adverse effect for individual– probability of adverse effect in population
Step by Step through Risk Assessment
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)
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
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
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
Step 2. Exposure Assessment - 3
• Indirect Exposure Estimation– extrapolation, ecological association– categorization (exposure matrices)– simulation– surrogate measurements– modeling
• surface water
• groundwater
• air dispersion
Step 3. Consequence AssessmentGeneral framework:
Probability ofOutcome/Magnitude ofOutcome
High Low
High Typically astructuralproblem
Unusualcatastrophicevents
Low Commonminorproblem
Seldom aconcern
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
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
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
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
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 = Bd, if set at 10-6, then derive
• D (allowable) = 106•B per lifetime
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
What Determines When a Risk is Acceptable?
Acceptability of Risk - 1
• Catastrophic potential –
• Familiarity +
• Understanding of risk +
• Scientific uncertainty –
• Controllability + (may be an illusion!)
• Voluntariness +
• Obvious benefit to community +
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 –)
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)
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
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