In Class Quiz Flashcards
Explain Reliability in terms of the probability that something will perform (explain the three criteria)
- Reliability defined as the probability that a system or product will accomplish its designated mission in a satisfactory manner
- more specifically, reliability is the probability that something will perform
- In a satisfactory manner
- For a given period
- When used under specified conditions
Reliability can be quantified from two different probability perspectives. Explain each of these.
- Probability of survival means that can expect the item to function at a satisfactory level for a particular percentage of the time
- Reliability may also be specified in terms of number of cycles, or number of successful functions completed.
Explain two means of increasing the reliability of a multi-component system
• Series Components:
Reliability can be improved by:
–decreasing number of components
–Increasing the individual component reliabilities
Reliability decreases rapidly as the number of components increases with greater negative slope for lower component reliability
• Parallel Components:
- May not be an overall advantage to parallel components due to added costs, weight, space involved
- May be difficult to parallel networks, especially with mechanical devices
- Gain in system reliability from adding more than three parallel components is relatively small
Explain how you would determine the increase in reliability that would result from each of the methods explained above. Provide equations to illustrate your solution.
• Series Network of Components
- Reliability of the system is the product of the reliabilities for the individual subsystems.
R = RARBRC
• Parallel Network of Components
- All components must fail to cause total system failure.
- For three components in parallel: R = 1 -(1-RA)(1-RB)(1-RC)
- If A,B and C are identical R = 1 -(1-RA)3 and so on for more redundant components
The term FMECA was used when discussing method of Reliability analysis. Explain what this acronym stands for and explain how it is used?
- Failure Mode, effects and Criticality Analysis (FMECA)
- Best used as “before-the-fact” tool to evaluate system design also used as an “after-the-fact” tool to evaluate and improve existing systems on a continuing basis
what is Fault Tree Analysis used for? Explain.
- FTA is a deductive approach involving the analysis of different ways in which a particular failure can occur and the probability of occurrence.
- May be applied during the early stages of design and is developed using a top-down fault-tree structure.
- Oriented to specific failure modes
Is Fault Tree analysis a top-down or bottom-up process? Explain
- Top-down ; Views the system as a whole
Explain three types of risk.
- Safety Risk: Threats to the life or health of the people involved
- Technical Risk: Threats to the successful execution of the mission due to operations or equipment problems.
- Programmatic Risk: Threats to the successful program development and implementation, that is, failure to meet funding commitments or meet scheduled milestones resulting in cancellation of program commitment
How is risk quantified? Use an equation in your explanation.
risk = probability of event x cost of event
Explain 3 potential threats you might identify (not all having to do with humans).
- Human – from individuals or organizations, illness, death, etc.
- Operational – from disruption to supplies and operations, loss of access to essential assets, failures in distribution, etc.
- Reputational – from loss of business partner or employee confidence, or damage to reputation in the market.
- Procedural – from failures of accountability, internal systems and controls, organization, fraud, etc.
- Project – risks of cost over-runs, jobs taking too long, of insufficient product or service quality, etc.
- Financial – from business failure, stock market, interest rates, unemployment, etc.
- Technical – from advances in technology, technical failure, etc.
- Natural – threats from weather, natural disaster, accident, disease, etc.
- Political – from changes in tax regimes, public opinion, government policy, foreign influence, etc.
Explain what is meant by estimating risk.
- Once you have identified the threats you face, the next step is to work out the likelihood of the threat being realized and to assess its impact.
- One approach to this is to make your best estimate of the probability of the event occurring, and to multiply this by the amount it will cost you to set things right if it happens. This gives you a value for the risk.
Explain at least 2 means for managing risk.
By using existing assets:
Here existing resources can be used to counter risk. This may involve improvements to existing methods and systems, changes in responsibilities, improvements to accountability and internal controls, etc.
By contingency planning:
You may decide to accept a risk, but choose to develop a plan to minimize its effects if it happens. A good contingency plan will allow you to take action immediately, with the minimum of project control if you find yourself in a crisis management situation. Contingency plans also form a key part of Business Continuity Planning (BCP) or Business Continuity management (BCM).
By investing in new resources:
Your risk analysis should give you the basis for deciding whether to bring in additional resources to counter the risk. This can also include insuring the risk: Here you pay someone else to carry part of the risk – this is particularly important where the risk is so great as to threaten your or your organization’s solvency. Note that you can even purchase travel insurance to guard against having to cancel a trip.
Explain two criteria for the adoption of a safety measure(s) in an existing technology, product, or industry.
- Risk/safety Criterion: A new safety device in an existing technology, product, or industry should be considered for use if it reduces the fatality rate of the industry, etc. below the total fatality rate of background risk. (This “background risk” level currently stands at approximately 0.4 accidental fatalities per 1000 people per year as of the year 2003.)
- Cost/Safety Criterion: For those technologies, products, or industries that fail the Risk/Safety Criterion, the new safety device should be mandated for use if its costs are roughly equal to or less than similar safety measures per fatality averted. (For automotive safety equipment, this cost currently stands at $260,000 per annual fatality averted.)
Probabilistic Risk Assessment (PRA) usually is used to answer three basic questions. What are they?
- What can go wrong with the studied technological entity, or what are the initiators or initiating events (undesirable starting events) that lead to adverse consequence(s)?
- What and how severe are the potential detriments, or the adverse consequences that the technological entity may be eventually subjected to as a result of the occurrence of the initiator?
- How likely to occur are these undesirable consequences, or what are their probabilities or frequencies?
Two common methods of answering the questions identified in question 1 are an event tree analysis and fault tree analysis. Explain each of these methods and be sure to explain if each is a top-down or bottom-up process.
Event Tree Analysis: Bottom-up.The event tree starts with an initiating event that starts the accident sequence. The event tree defines top events, each of which can be analyzed with a fault tree that develops more basic causes such as hardware or human faults.
Fault-Tree Analysis: Top-down
