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faulttree·NUREG-0492 / IEC 61025·engineering, education·complexity 2/3·since v0.6.5

Water overheating (classic textbook tree)

The canonical introductory fault tree — an OR top over an AND sub-fault and an OR no-voltage branch, with a probability on every basic event. A faithful, quantified reproduction of the standard worked example.

For the reliability-engineering instructor

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Water overheating Fault tree for "Water overheating": 1 top, 2 intermediate, 5 basic. 4 minimal cut sets: {C}, {D}, {E}, {A, B}. Single points of failure: C, D, E. P(top) = 0.371 (rare). Water overheating Water overheating Circuit failure andno warning lamp A Chip failure p=0.05 B Warning lamp burned p=0.03 E Booster failure p=0.02 No voltage at input C No burn in network p=0.12 D Fuse blown p=0.23 P(top) = 0.371 (rare)
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What this shows

The fault tree every reliability course opens with, rendered with computed cut sets. The top event ORs three branches: an AND sub-fault F (a circuit failure and a dead warning lamp must coincide), a direct booster failure E, and an OR no-voltage branch G.

The minimal cut sets mix orders: {E}, {C}, {D} are order-1 single points of failure (any one trips the top event), while {A, B} is order-2 (both the chip and the lamp must fail together). Each is boxed in red, single points of failure in the strongest red, and the top-event probability is computed from the per-event values — the deductive, quantified reading a fault tree exists to give.

Fault tree syntax →