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36 Cards in this Set

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  • Back
definition: root cause
The event or circumstance that directly leads to an occurrence
definition: root cause analysis (RCA)
A systematic procedure that uses the results of the other analysis techniques to identify the predominant causes of the accident
acronym: RCA
root cause analysis
the 4 basic characteristics of root causes
• Expressed as a specific underlying cause, not a generalization
• Can be reasonably identified
• Must be expressed as something that can be modified
• Must produce effective recommendations for prevention of future accidents that stem from the root cause
the 5 broadly-defined RCA approaches
• Safety-based (originated from accident analysis and occupational safety & health)
• Production-based (evolved from quality control procedures for industrial manufacturing
• Process-based (like production-based, but includes business processes)
• Failure-based (from failure analysis; used primarily in engineering and maintenance
• Systems-based (combines above four approaches with change management, risk management, and systems analysis concepts)
definition: causal factors
The agents that directly result in one event causing another
the 4 steps in the RCA process
1. Data collection
2. Causal factors charting
3. Root cause identification
4. Recommendation determination and implementation
definition: failure mode and effect analysis (FMEA)
An analysis that reverses the direction of reasoning in fault tree analysis by starting with causes and branching out to consequences
acronym: FMEA
failure mode and effect analysis
definition: failure mode
The manner in which a perceived or actual defect in an item, process, or design occurs
definition: effects analysis
The study of a failure’s consequences to determine a risk event’s root cause(s)
definition: indenture level
An item’s relative complexity within an assembly, system, or function
definition: local effect
The consequence of a failure mode on the operation, function, or status of the specific item or system level under analysis
definition: next-higher-level effect
The consequence of a failure mode on the operation, function, or status of the items in the indenture level immediately above the indenture level under analysis
definition: end effect
The consequence of a failure mode on the operation, function, or status of the highest indenture level
FMEA’s primary goal: ensure customer safety & production of quality products through these 5 outputs:
• Improvement in the design of procedures and processes
• Minimization or elimination of design characteristics that contribute to failure
• Development of system requirements that reduce the likelihood of failures
• Identification of human error modes and their effects
• Development of systems to track and manage potential future design problems
the 5 steps of the FMEA process
1. Determine scope and objective(s)
2. Assemble team
3. Define system components and their functions
4. For each component, identify potential causes and effects of failure
5. Develop responses to prevent or mitigate failure
definition: criticality analysis
An analysis that identifies the critical components of a system and ranks the severity of losing each component
the 4 categories of failures used in criticality analysis
Category 1 – results in excessive unscheduled maintenance
Category 2 – results in delay or loss of operational availability
Category 3 – results in potential mission failure
Category 4 – results in potential loss of life
definition: risk priority number (RPN)
The product of rankings for consequence, occurrence, and detection used to identify critical failure modes when assessing risk within a design or process
acronym: RPN
risk priority number
the 3 components of a RPN
• Consequence – rate the severity of the effect of the failure
• Occurrence – rate the likelihood that the failure will occur (failure rate)
• Detection – rate the likelihood that the failure will NOT be detected before it reaches the customer
definition: criticality
A combination of the risk priority number elements of consequence and occurrence, used to determine the relative risk of a failure mode and effects analysis item
4 advantages of FMEA
• Widely applicable to many different system modes
• When used early in design phase, can reduce costly equipment modifications
• Can improve quality, reliability, and safety of a product or process; can improve organization’s image and competitiveness by possibly reducing scrap in production
• Emphasizes problem prevention by identifying problems early in the process and eliminating potential failure modes
3 disadvantages of FMEA
• When used as top-down tool, may only identify major failure modes in system
• Other analysis methods might be better suited for this type of analysis
• Analyzing complex multilayered systems can be difficult and tedious with FMEA; studies that are not adequately controlled and focused can be time-consuming and costly
definition: fault tree analysis (FTA)
An analysis that takes a particular system failure and traces the events leading to the system failure backwards in time
acronym: FTA
fault tree analysis
p(S and T and U)
p(S) x p(T) x p(U)
p (H or I or both)
p(H) + p(I) - p(H and I)
p(H) + p(I) - [p(H) x p(I)]
the 5 steps of FTA
1. Identify a specific harmful event to construct the fault tree; be as specific as possible so that events contributing to the failure can be fully described
2. Diagram, in reverse order, the events that led to the harmful event
3. Determine whether the events leading to any other event on the fault tree are connected by an “and” gate or an “or” gate
4. Evaluate fault tree to determine possible system improvement
5. Suggest risk control measures to management that can treat the identified hazards
3 underlying assumptions of FTA
• All components exist in only 1 of 2 conditions (success/operational vs. failure/not operational)
• Any system component’s failure is independent of any other component’s failure
• Each failure has an unchanging probability of occurrence
5 limitations of FTA
• If uncertainty about probabilities of underlying/base events, probability of top event will also be uncertain
• Important pathways to top might not be explored if causal events are omitted from the fault tree
• Because fault tree is static, it may need to be reconstructed if circumstances or procedures change
• Human error is difficult to characterize in a fault tree
• “Domino effects” or conditional failures are not easily included in a fault tree
4 steps of a 5 Whys analysis
1. Completely describe the specific problem under investigation
2. Ask why that particular problem occurred; determine the answer
3. If answer does not reveal problem’s root cause, ask why it occurred
4. Repeat steps 2 & 3 until root cause of original problem is determined
3 advantages of 5 Whys analysis
• Can determine root cause of a problem
• When several root causes are found, can help determine relationship among them
• Usually does not require statistical analysis or data collection
5 disadvantages of 5 Whys analysis
• Investigators tend to stop analysis after first determination instead of asking additional questions to discover problem’s root cause
• Investigators tend to focus on only one answer to each question
• Organizations sometimes do not help the investigator ask the right why questions [what?]
• An uninformed investigator cannot ask relevant questions
• Different investigators will discover different causes for the same problem (this can be an advantage if several root causes exist for the same problem)
9 steps of developing a fishbone diagram
1. Team agrees on problem statement
2. Write problem statement on far right of diagram, encircle, draw horizontal arrow from L to R pointing to statement
3. Team brainstorms major causes of problem
4. Facilitator writes categories of causes as branches off main arrow
5. Team brainstorms possible specific causes (may use 5 Whys)
6. Facilitator writes specific causes as branches off categories
7. For each specific cause, brainstorm sub-causes
8. Before ending, focus on areas with the fewest ideas
9. Develop and implement remedies to prevent recurrence of problem