4. Risk Assessments Flashcards
(27 cards)
risk
potential negative impact to something of value that might result from a future event
joint probabilities of an occurence of an event and its consequences
risk involves trying to understand uncertainty
different types of risks
-project risks; schedule/resources
-product risks; quality/performance of product
-business risk; orgnisation finances/resources
-operational risks; facility, equipment, people
-enviro. risks; to and from enviro.
-health risk; human, short/long-term/immediate
risk equation
risk = probability of an accident x losses per accident
risk = likelihood of occurence x consequence of occurence
probability vs likelihood
probability; hypothesis treated as a given (data may vary)
–> figuring out the chance the risk will happen
likelihood; data is given (hypothese may vary)
–> chance that a risk will impact us
risks characterized by
probability of an adverse outcome
type + severity of adverse outcome
timing of adverse outcome
distribution of adverse outcome
size of exposed population/enviro.
certainty of risk estimates
risk acceptance
always balancing risks with benefits, BUT might disagree on whther risk acceptable or not
accepting consequences of a risk happening, but likelihood and consequences can change over time ad no longer be acceptable
hazard
situation posing a level of threat to life, health, property, enviro. potentially harmful situation
source of potential harm
harm = injury/damage to enviro. or people
4 types of hazards
a. dormant; situation having potential to be hazardous, currently no one affected
b. potential;hazard in position to affect, likely needs further risk assessment
c.active; hazard is certain to cause harm, no intervention possible before it occurs
d. mitigated; actions taken to ensure potential hazard not incident, may not be absolute guarantee of no risk (reducing danger)
Hazard causes
a. natural
b. human-made
accident vs incident
incident; sequence of actions/events
accident; incident’s consequences
All accidents are incidents, not all incidents = accidents
Risk analysis (2 parts)
quantify the potential harm (risk assessment)
-what can go wrong
-likelihood of going wrong
-consequences
+
evaluate the effectiveness of proposed remediation (risk management)
-what can be done
-options available, tradeoffs, costs, benefits, risks
-impacts of mgmt decisions on future options
Risk analysis guiding principles
-scope definition
-hazard location
-failure mode effect analysis
-failure likelihood analysis
-consequences assessment
-risk characterization
-uncertainty/sensitivity analysis
-documentation
-expert review/verification
-analysis update
4 risk analysis methods
a. failure mode effect analysis (FMEA)
b. fault tree analysis (FTA)
c. event tree analysis (ETA)
d. bow-tie analysis (BTA)
failure mode effect analysis (FMEA)
hazard identification
involves interpreting the analysis and expressing results in terms of some risk metric
S x O x D = RPN (risk priority number)
S x O = criticality (second most weight)
severity; estimate how severe public perceive effect of failure. given the most weight
occurence; estimate of likelihood that the cause will = failure mode
detection; estimate of effectiveness of control to prevent failure mode (assuming it occured)
RPN; from 1-1000, measure help identify critical failure modes associated with process/design
–> any failure mode that has an effect resulting in severity 9-10 would have to top priority
fault tree analysis (FTA)
likelihood of system failure
focus on preventive measures
–> multiple causes leading to an event
identifies, models, evaluates unique interrelationship of events leading to failure, undesirable events, unintended events. identifies all possible causes of a specified undesired event (top event)
deductive analysis, reasoning what can lead to occurence of specified undesired event (top down manner, from general to specific
top event = failure
basic events = root causes
intermediate events
logic gates (AND, OR)
=fault tree
steps:
1. define system, top event (potential accident) + boundary conditions
2. fault tree
3. analysis of fault tree
4. report results
–> graphic tool
–> qualitative insight to the system
–> can be used for quantitative assessmet system reliability
–> mainly safety engineering to quantitatively determine probablity of a hazard
event tree analysis (ETA)
consequence of system failure
focus on mitigation measures
–> multiple consequences after an event
accidental event may = different consequences (inductive reasing, bottom-up approach)
potential consequences may be illustrated by consequence spectrum
probability that an accidental event will lead to unwanted consequences depends on whether barriers are functioning or not (well dsesigned systems have 1+ barriers implemented to stop/reduce consequences of potential accidental events).
additional events: listed together as barriers (as far as possible in sequence), described as worst case statements
output events; usually 2 alternatives (true vs false)
–> consequence analysis
bow-tie analysis (BTA)
risk of system failure
integrated probabilistic technique analyzing the accident by scenarios, assessing the probability/pathways of occurences
couples FTA + ETA by using common top event as critical event
causes; fundamental reasons resulting in failure (basic events)
fault tree (FT); graphic pathways of causation leading to undesired event which is top-event + interactions of causes (basic events, intermediate, logic gates)
critical event (CT); top event of FT = initiating event for ET = critical event
event tree (ET); sequences possible consequences of CE considering barriers
outcome event (OE); final consequences from systematic propagation of CE through barriers
pre-event side = FT
–> preventive controls
post-event side = ET
–> recovery controls
risk management ALARP
as low as reasonably practicable
decision actions, control strategies, interventions
estimated value of risk, acceptable value of risk, risk after intervention (risk mgmt)
uncertainty
measure of the “goodness” of an estimate
how closely estimated value relates to/represents reality
arises from lack/insufficient knowledge-impossible to exactly describe existing state or future outcome
state where 1+ possible outcome can exist
large part of EIA practice is about ….
(3)
- identifying the potential negative outcomes or risks, of a project.
- managing/mitigating risks (making decision with knowledge of risks and potential outcomes)
- perceived risks to people, ecosystem, enviro.
–> what participation asks proponents to account for and mitigate
critiques of FTA/ETA
-assume events (basic events) are independent
–> interdependence among events
-incompleteness/partial ignorance + imprecision
–> likelihood values of input events, requires known probablities
= unrealistic
=uncertainty
–> evidence theory; multisource knowledge = more reliable information about event probability (knowledge is socially constructed, so always incomplete)
uncertainty associated with a system is proportional to its…
+
uncertainty arising due to lack of…
DATA UNCERTAINTY
complexity (arising from vaguely known relationships among its entities, and randomness in governing mechanisms)
–> relationships between cause/effect often not well understood
–> often non linear behaviour, combined effects of contributing factors= sub/superadditive
DEPENDENCY UNCERTAINTY
information on dependencies among events (FTA/ETA assume interdependence among risk events to determine joint probability (risk))
vulnerability vs capacity
vulnerability; how susceptible something is to harm
capacity; ability to cope with risk if it happens
–> vulnerability>capacity = potential impact of risk higher
–> both are linked, depend on the degree to which people/communities have access to resources to deal with risk
2 ways of analyzing risk
a. qualitative risk analysis; prioritize the identified risks on a defined scale based on their likelihood of occurence + their impacts
b. quantitative risk analysis; defines probability of an event occuring
(BTA, ETA, FTA)
–> which one to use depends on data available, type of risk analyzed, amount time
