CSP-11 CSP-11 D2.06 · Domain 2 · Program Management · 25%
FTA
A tank-overfill review shows two independent shutdown channels must both fail before the high-high level trip is lost, but a single shared power failure can defeat both. Management asks for one RPN. Your decision: is this a row-ranking problem, or a top-event logic problem with AND/OR paths and a common-cause cut set?
Updated . Independent CSP-11 practice. Not BCSP-endorsed. No pass guarantee.
Class 23 · Current preview
Explore the new Fault Tree Analysis master lecture
This temporary preview adds a worked model, interactive gate calculator, visual tree and explained practice questions.
Open the master lecture →Decision rule
FTA explains how a top event can occur. AND requires every input; OR requires any input.
Use FTA when combinations of failures matter. Do not use it as a substitute for removing the source.
In 20 seconds
- FTA explains how a top event can occur.
- AND requires every input; OR requires any input.
- FTA is top-down for a defined top event — not a brainstorm without a top gate.
- AND gates need all inputs; OR gates need any input.
How to apply FTA
THEORY: Top event, intermediate gates, basic events. Independent events multiply on AND if probabilities are given and independence is true. CALC: Teaching: two independent 0.1 events on AND → 0.01. On OR, 0.1+0.1-0.01 = 0.19. TI-30XS: 0.1x0.1= and 0.1+0.1-0.01=. Do not invent probabilities. FIELD: Dual isolation both fed from one air header — not independent, so not two AND inputs. ASSESS: An FTA after steel is ordered that cannot change the design is a binder.
Worked case
Wrong first move: draw a pretty tree and keep shared utilities. Correct move: fix independence or reduce the source; then quantify only with given, independent data.
Why the rule holds
Related: 24, 91, 113, 120.
Same rule, different setting
A board wants “the RPN” for a well-control event that needs two independent barriers to fail together. Someone opens an FMEA spreadsheet. You are the CSP. The question is whether this is an FTA problem.
A board wants “the RPN” for a collapse that needs two independent shores to fail together. Someone opens an FMEA spreadsheet. You are the CSP. The question is whether this is an FTA problem.
Picture / model
Read the tree from the top event downward to causes, then upward to test whether the stated combination is sufficient. An AND gate needs every branch; an OR gate needs any one branch. A minimal cut set is a smallest sufficient combination within the model; challenge missing shared causes.
Exam traps
Original SafePath contrasts for FTA. These are study traps, not recalled BCSP items.
| Trap | Correct read |
|---|---|
| FTA | Top-down logic of combinations (AND/OR, cut sets) |
| FMEA | Bottom-up single failure modes, RPN = S×O×D |
| Bowtie / safety case | Barriers on causes and consequences; demonstration to a decision maker |
| RPN on an AND gate | TOOL error — detection score is not P(A and B) |
Field move
An AND of two barriers is not the probability that someone misses a horn.
Scenarios
Scenario 1 · Fundamental · CSP-11 D2.06
A tank overfill requires two independent level loops to fail. The team opens FMEA and ranks “operator fails to notice horn” as worst RPN. Best CSP call?
Best action: Wrong tool: combinations of independent barriers want FTA (or a quantified bowtie), not a single-point RPN on detection.
Why: Evaluate the best response. Overfill needs two independent level loops to fail. The team ranked an operator missing the horn. The best call is the wrong tool: combinations of independent barriers want a fault tree or a quantified bowtie, not a single-point detection score. Keeping the single-point…
Scenario 2 · Applied Scenario · CSP-11 D2.06
A chemical terminal team must show how a transfer-release top event can occur through combinations of failures. Which drawing is an FTA?
Best action: A top event decomposed through AND/OR gates to basic events and cut sets.
Why: Evaluate the best response. The team must show how a transfer release occurs through combinations of failures. The best drawing is a top event decomposed through AND and OR gates to basic events and cut sets. A spreadsheet of severity, occurrence, and detection is a failure-mode table, not a fault…
Scenario 3 · Applied Scenario · CSP-11 D2.06
An FTA shows an OR of “no dike” OR “dike undersized.” A dike can still be built. The team funds a better detector. Best action?
Best action: Build/size the dike (consequence barrier / engineering) rather than detection-only while that row is open.
Why: Evaluate the best response. The tree shows no dike or an undersized dike, and a dike can still be built. The team funded a detector. The best action builds or sizes the dike rather than detection only while that row is open. Keeping the detector because the tree always funds electronics leaves the…
If the stem says this
| Stem signal | Best direction |
|---|---|
| the top event is undefined | define the top event before building gates |
| common-cause links two basic events | model dependence — do not assume independence |
| management wants FTA after the design is frozen with no change path | reject theater — FTA must be able to change controls |
| the question is single-component failure modes only | consider FMEA instead of forcing FTA |
| two answers work | higher hierarchy / system / design |
Check before you leave
- ✓ FTA is top-down for a defined top event — not a brainstorm without a top gate.
- ✓ AND gates need all inputs; OR gates need any input.
- ✓ Basic events need credible probabilities or qualitative rankings.
- ✓ Independence assumptions fail when common-cause is ignored.
- ✓ FTA informs design and cut sets — it is not decoration after a decision.
- ✓ Minimal cut sets show the fewest failures that cause the top event.
Blueprint mapping
FTA is the SafePath study class for CSP-11 D2.06 inside CSP-11 Domain 2, Program Management (25%). A high-weight management domain focused on measuring performance, investigating incidents, managing change, building systems, leading people, controlling records and resources, and interpreting data.
SafePath uses the publicly posted CSP-11 outline as a study map. It does not reproduce official exam content, and it is not affiliated with or endorsed by BCSP or Pearson VUE.
Practice / flashcards / formulas
More classes in Program Management
Nearby lessons mapped to the same CSP-11 domain.
CSP-11 D2.06
Other classes on this task
Guides that use FTA
- Oil and gas safety study guideProcess safety, change, and investigations
- CSP application and exam guideEligibility, scheduling, and exam method
- CSP-11 exam prep guideDomain weights, sample items, and a study sequence
- CSP-11 blueprint and weightsSeven published domains and the class map
- Seven-domain study directoryScope, tasks, and links into each lesson
FTA study questions
- What decision does the FTA class train?
- FTA explains how a top event can occur. AND requires every input; OR requires any input. This is independent SafePath CSP practice for CSP-11 D2.06. It is not an official BCSP item and it is not a pass guarantee.
- What exam trap shows up in FTA?
- A common miss treats this as sufficient: FTA The stronger read is: Top-down logic of combinations (AND/OR, cut sets)
- How does FTA map to the CSP-11 blueprint?
- SafePath maps this class to CSP-11 D2.06 in Domain 2, Program Management (25% of the published blueprint). Use the public outline for study planning. SafePath is not affiliated with or endorsed by BCSP.
Verify
Verify: Confirm current certification requirements with BCSP and technical requirements with the cited authoritative standard.