risk analysis Flashcards
Safety (Process)
A business objective directed at
preserving and protecting workers, the public,
the environment, and assets against harm
resulting from known conditions, natural
occurrences, malicious acts, accidents, and
risks…
Safety (Condition)
Condition in which there is low probability
that harm will occur
System Safety
The application of engineering and
management principles, criteria, and techniques to
achieve acceptable mishap risk, within the constraints of
operational effectiveness, time, and cost, throughout all
phases of the systems life cycle
or
an optimal degree of safety, established
within the constraints of operational effectiveness, time,
and cost, and other application interfaces to safety, that
is achievable throughout all phases of the system life
cycle
Accident/Mishap
Undesirable event or a series of undesirable
events that result in harm
System
An integrated composite of people, products, and processes that provide a capability to satisfy a stated need or objective
Hazard
Conditions or events in a system that can result in harm
Risk
Likelihood (probability) and severity of a loss (consequence).
or
cost of mishaps stemming from a particular hazard over
life of system
Hazard probability
likelihood of adverse consequence from particular hazard
Hazard severity
Assessment of consequences of specific hazard
Examples of Hazards
Leak of photocopy fluid
Leak of toothpaste
Fire
Radiological release
Death
Total Risk
Unacceptable risk that is eliminated
unacceptable risk that is controlled
residual risk
Residual Risk
Acceptable and unidentified risk
Exposure
The time interval over
which hazard exists
What is the area under the curve of consequence and probability?
Total risk of the hazard
What should you assign each hazard?
Th worst credible consequence (most severe
outcome that can reasonably be expected
to occur) and use this to assign a risk
assessment level (as representative of the
whole hazard)
Safety analysis
Analysis by means of
appropriate analytical tools that
establishes and confirms the design basis
for the items important to safety; and
ensures that the overall plant design is
capable of meeting the acceptance criteria
for each plant state
Design basis
The range of conditions and
events taken explicitly into account in the
design of the facility, according to established
criteria, such that the facility can withstand them
without exceeding authorized limits by the
planned operation of safety systems
Covers plant states during
- Normal Operation
- Emergency
- Maintenance/Testing
What is the philosophy behind system safety?
- Loss Prevention - Complete removal of all hazards
- Secondary Prevention (Loss Control) when hazard cannot be completely removed. System (components, people, environment) protected so that exposure to hazards less likely or consequences less severe.
- Trade-offs
Objective of system safety?
Achieve a minimal level of
risk within the constraints of
operational effectiveness, time, and
cost.
or
can help to reduce human
errors within the sociotechnical system (design,
training, operations, plant management,
organizational env, safety culture …)
System Safety Principles and Methods to
determine how system can fail, how can cause
injury, death, illness, damage, loss of
equipment or property, data, damage to
environment.
Systematic
Hazard Identification
Hazard Elimination
Risk Control
System Safety Process
Define Objectives
System Descriptions
Hazard Identification
Risk Analysis
Risk Assessment
Decision Making
Validation of Control
Modify System/Process
Define Objectives
Define the objectives of the
system under review -
business plans and operating
specifications
System Description
- interactions among people,
procedures, tools, materials,
equipment, facilities,
software, and the
environment - data available
Hazard Identification: Identify
Hazards & Consequences
- internal and external sources
-Create Preliminary Hazard List (PHL)
-Group by functional equivalence for analysis
-Determine Hazard scenarios
-Determine consequence (undesired event) resulting from the hazard scenarios - Hazard scenarios may addressthe following: who, what where, when, why and how.
- Need to determine and document condition and the
consequences that will be used during risk analysis
Risk ANALYSIS: Analyze
Hazards and Identify Risks
- Risk ANALYSIS -Characterize hazards fortheir likelihood and severity
-What can happen when.
-Can be Qualitative or Quantitative analysis.
-If no historical data for, or cannot quantify, a particular
hazard, still need to address
-Risk Assessment Matrix is normally used to determine
the level of risk
Risk ASSESSMENT:
Consolidate & Prioritize
Risks
- Risk ASSESSMENT - combining the impacts of
risk elements discovered in risk analysis
-Compare them against Acceptability Criteria - Consolidate risks into Risk Sets to be jointly mitigated,
combined - Use results in Decision Making.
- Create Prioritized List of Risks
Decision Making: Develop
Action Plans
-Using prioritized risk list.
-Start with highest priority risks
- How to address each risk and Choose how to deal
with risks.
- T.E.A.M. (Transfer, Eliminate, Accept, or Mitigate).
- Modify Action Plans?
Safety order of
precedence
1) Design for minimum risk
2) Incorporate safety devices
3) Provide warning devices, or
4) Develop procedures and training.
similar to HOM
Safety order of
precedence
1) Design for minimum risk
2) Incorporate safety devices
3) Provide warning devices, or
4) Develop procedures and training.
similar to HOM
Validations and Control: Evaluate Results
of Action Plan for Further Action
-Conduct analysis to determine if the planned approaches/actions are effective in reducing risk.
-Collect triggering events and data to be collected
-Review data and results.
-Review on ongoing basis status of prioritized risks.
-If the residual risk is acceptable, document changes to the system
Document rationale for acceptability of
residual risk.
-if residual risk is unacceptable,
Plan modification to system/process or
other action
Modify System/Process (if
needed
-Determine why status of a risk should change
-Determine why mitigating action does not produce the intended effect,
-Was correct hazard addressed?
-Does system/process need to change?
- Repeat system safety process.
hazards in bhopal incident
the chemicals they stored
heat
the pipes being interconnected
what happened in bhopal
insecticide plant that stored many different chemicals that needed to be combined to form the final product. one was deemed dangerous enough to be low quantities but another (MIC) had a lot more
maintenance happened and they skipped putting in a steel barrier. a pipe clogged causing water to rush through the system and fill into a tank of a chemical.
that chemical was not supposed to have any contact with water because it caused a reaction that heated up the chemical into a gaseous form
the pressure gauge dials regularly read wrong, and this one was off the charts (people tend to ignore because they think its faulty)
the system that cools the underground chemical tanks was not functioning, senior management had turned it off
there was also a gas scrubber but it was off for maintenance and too small to help that quantity anyway
the pressure built up in the underground tank and the pressure relief valve blowing the gaseous chemicals into the city of bhopal killing thousands of residents
Person Approach for mitigating human error
-signs “WORK SAFE”
-Influence individual behaviour – penalties, adding
more and more to procedures.
-“Naming, Blaming, Shaming”
(union carbide blames a disgruntled employee)
Systems Approach for mitigating human error
-look for events and “upstream
systematic factors” that caused the human error to
happen
- Look for recurrent error traps.
- Design defences into the system/hardware
-Look at equipment AND processes
expect the errors, humans are fallible
(bhopal could’ve had a valve not a plate)
What is the swiss cheese model and its reasoning?
picture some moving swiss cheese slices - things travel through some holes and stop at others
hard to predict when active failure will occur, latent conditions can be identified and remedied
pro active risk management
Active Failures
-unsafe acts by people (slips, lapses,
fumbles, procedural violations ….)
-Direct, short-lived impact on defences
-not helpful in preventing other events
Latent Conditions
– virtually all acts have causal history
(extends back in time and through levels of the system)
-From decisions made in design, builders, procedure-
writers, management
-can be dormant
-Error Provoking Conditions (e.g., time pressure results in cutting corners….)
- Holes or Weaknesses in Barriers (untrustworthy
alarms/indicators, unworkable procedures, design inadequate ..)
Risk management
Limit the incident of dangerous errors (never
100%
Create systems which are tolerant to
occurrence of errors and contain damaging
effects
System Safety Methods and
Techniques
Human Factors Analysis
Human Reliability Analysis
Task Analysis
Walkthrough Task Analysis
Failure Modes and Effects Analysis
(FMEA)
Hazard and Operability Assessment
(HAZOP)
Failure Mode and Effects Analysis (FMEA)
Best for mechanical and electrical hardware systems
1. consider how failure modes of each system component can result in system problems.
2. ensures safeguards against each problem are in place.
Consider how failures can be detected
Recommendations for suitable control measures
May lead to design changes
Quantitative version of FMEA is called FMECA (Failure Modes and Effects and Criticality Analysis)
Hazard and Operability Assessment (HAZOP)
-Structured and Systematic Review
-examination of a planned or existing process or operation
-to identify and evaluate problems that may represent risks to personnel or equipment, or prevent efficient operation.
- For example, in a chemical plant, a pipe may have the intention to transport xxx kg/s of yy% product zz at aaa°C and a pressure of bb bar from a pump to a
valve. The intention of the valve is to cccc.
- HAZOP determines significant Deviations from each intention, feasible Causes and likely Consequences.
- Based on understanding cause and effects of potential
hazards
