Fault tree (FTA)
Quantitative fault-tree analysis in the IEC 61025 notation. Build the tree from AND / OR / k-out-of-n / INHIBIT gates over basic events carrying probabilities, and the engine computes the top-event probability exactly rather than by the rare-event approximation, ranks each basic event's Birnbaum and Fussell-Vesely importance, and enumerates the minimal cut sets. The safety analysis a boxes-and-lines drawing cannot perform.
In the same space
Most users come to Fault tree (FTA) from Isograph FaultTree+, ITEM ToolKit, Visio FTA stencils or RAM Commander. flowss runs this engine in the browser — no install, shareable via URL, exportable to PNG / SVG / PDF / source.
Syntax at a glance
top "Cooling lost" = AND(pump_fail, backup_fail)
gate pump_fail = OR(motor, power)
event motor "Pump motor" p=0.02
event power "Bus power" p=0.001Paste this in the Studio code pane to see Fault tree (FTA) render live. The full grammar is at the upstream-docs link above.
Sample templates
All 13 →Loss of decay heat removal after a reactor trip: two redundant paths, a two-of-three auxiliary feedwater vote and an INHIBIT gate for the fouled service-water strainer, quantified over a one-year mission.
Total hydraulic power loss on a three-system narrowbody over a five-hour leg, where a single common-cause fluid contamination event sits in all three branches and dominates a picture that looks fully redundant.
Tier III power path from utility through a two-of-three generator vote and an N+1 UPS pair, exposing the transfer switch and the final rack circuit as order-one cut sets no amount of upstream redundancy touches.
Loss of ward oxygen at an acute hospital: bulk evaporator and emergency manifold in parallel, with the manifold gated by an INHIBIT on unreplaced reserve cylinders, plus three pipeline faults that bypass the redundancy entirely.
Dual diagonal hydraulic circuits backed by an electric park brake over 300 driving hours, showing how the shared master cylinder and reservoir turn two independent-looking circuits into one, and the 12 V supply into a common mode.
Subsea BOP failing to seal a well over one section, with the blue and yellow control pods feeding BOTH the shear rams and the annular preventer — a shared gate drawn once and transferred, and the reason the two seals are not independent.
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