System Safety Analysis: Fault Trees and FMEA practice questions for the ASP exam

A safety engineer is building a fault tree for the top event 'press operator's hand enters the point of operation during a cycle.' A colleague asks her to add every other way the press could fail, including hydraulic leaks, motor overheating and a worn clutch lining, so the tree 'covers all system failures.' She declines. What is the best justification for declining?

1. A.A fault tree must include every hardware failure but may omit human errors because they cannot be modeled.
2. B.A fault tree is tailored to one particular failure mode and includes only the faults that contribute to that top event.
3. C.A fault tree can only be built once probabilities are available for every possible failure of the system.
4. D.A fault tree is a quantitative model, so only failures with known failure rates can be included.

A safety analyst is building a fault tree for a conveyor line's emergency-stop system. She has chosen "E-stop fails to halt the conveyor" as the top event. For the next level of the tree, a junior colleague proposes listing the root causes he suspects, such as corrosion on the relay contacts, operator inattention during training, and a supplier's lapse in quality control. Which response best reflects the correct fault tree method?

1. A.Replace the list with the immediate, necessary, and sufficient causes of the top event, then treat each as a sub-top event and develop it further
2. B.Accept the list, because the second level should name the most basic underlying causes so the tree is as short as possible
3. C.Accept the list, but only if each cause is assigned a probability before the tree is developed further
4. D.Replace the list with the component designer's quality-control and environmental effects, since these define the limit of resolution

A safety analyst is building a fault tree for a cooling system. One team member proposes classifying components for the analysis. The system includes a motor-driven pump, a solenoid valve that opens and closes to modify flow, a steel support bracket that only carries the pipe load, and a welded pipe section. Which classification of these items is consistent with the handbook's definitions?

1. A.Solenoid valve and support bracket are active because both are involved in controlling system response
2. B.Pump and welded pipe are active because they handle fluid; valve and bracket are passive
3. C.All four are passive because none of them originates its own signal
4. D.Pump and solenoid valve are active; support bracket and welded pipe are passive