fault trees

Scenario: "No cooling water flow to heat exchanger"

Write the top event as "No CW flow to heat exchanger", then branch into the two flow paths failing, and under each path include pump failure, power failure, and if valves are shown, valve failure. Use AND if both parallel paths must fail for total loss of flow, and OR within each path for the individual causes.

Scenario: two parallel pumps supplying one service

Write each pump train separately underneath the top event, then show that total failure occurs only if train A fails AND train B fails. Within each train, use OR for mechanical failure, electrical failure, or valve failure.

Scenario: "Sprinkler system failed to operate"

Write the top event as sprinkler system failure, then split into fire detection system failure OR water supply failure. Under detection failure write smoke detector failure and heat detector failure. Under water supply failure write pump did not start, nozzles blocked, and any maintenance/design causes such as missing filter or dirt.

Scenario: "Release from PRV"

Write the top event as release from the PRV, then below it write the immediate causes as overpressure reaching PRV set point OR PRV malfunction if relevant. Under overpressure, include process causes such as blocked outlet, excessive inflow, high temperature, or control failure. If the question gives LT/level trip and PRV, show overfilling / overpressure plus trip/protection failure as contributing branches.

Scenario: "Tank overfill" or "tank vents release flammable liquid/vapour"

Write the top event as tank overfilled or overflow release, then branch into inflow continues AND high level protection fails. Under inflow continues, include operator fails to stop transfer, valve fails open, or incoming pipeline cannot be isolated. Under protection failure, include stuck level gauge, high-level alarm failure, and poor procedures / poor maintenance if the scenario supports it.

Scenario: "No shutdown on high pressure / high temperature"

Write the top event as shutdown fails on demand, then branch into sensor fails to detect deviation, logic/trip system fails, final element fails to act, and operator fails to intervene if manual backup exists. This is the standard protection-layer style answer.

Scenario: runaway reactor / quench system fails

Write the top event as reactor damage due to high temperature. Then use the main branches no quench flow, quench valve fails to open, feed valve remains open, quench tank empty, and operator fails to respond to alarm. Under alarm failure include temperature sensor failure and alarm failure.

Scenario: "Loss of containment from corroded pipe/vessel"

Write the top event as loss of containment or gas leak from corroded vessel/pipe, then branch into wall thinning/corrosion, material failure, inspection failure, and maintenance failure. If water/H2S/corrosive service is mentioned, include those as lower-level causes for corrosion.

Scenario: simple exam fault tree with one protective device

The safest template is: top event → process deviation occurs AND protection fails. Under process deviation put the process cause. Under protection failure put sensor, alarm/trip, valve/final element, and human response if relevant.