Free and open-source fault tree analysis.

• For rudimentary documentation, see DOCS.md.
• For an overview of the mathematics, see MATHS.md.
• For example fault trees, see examples/.

• Enforces declaration of at least one value of time t.
• Supports the general fault tree analysis framework where objects can have both a failure probability q(t) and a failure intensity ω(t) (with failure rate λ(t) = ω(t) / (1 − q(t))).
• Supports Monte Carlo (sampling of distributions) for failure parameters out of the box.

• Does not support negative logic (NOT gates). Only supports coherent fault trees (i.e. those whose logic is reducible to AND gates and OR gates).
• Does not support common cause failure groups.

PFTA reads a textual representation of a fault tree. For example:

- times: 1, 2, 3, 5, 10, 100, 1000 - time_unit: h - seed: Candley McCandleface - sample_size: 1000 Gate: CAN - label: Candlelight fails - type: OR - inputs: IGN, EXP, EXT Gate: IGN - label: Candle fails to ignite - type: AND - inputs: MAT, LTR Event: MAT - label: Single match fails to ignite candle - model_type: Fixed - probability: triangular(lower=0.1, upper=0.3, mode=0.2) - intensity: 0 Event: LTR - label: Lighter fails to ignite candle - model_type: Fixed - probability: loguniform(lower=0.001, upper=0.01) - intensity: 0 Event: EXP - label: Candle explodes on ignition - appearance: Undeveloped - model_type: Fixed - probability: 0 - intensity: 0 Event: EXT - label: Candle extinguishes - model_type: ConstantRate - mean_failure_time: 3 - mean_repair_time: inf 

This allows for text-based version control of a fault tree.

Output files consist of:

• a table (TSV) of events,
• a table (TSV) of gates,
• a table (TSV) of cut sets under each gate, and
• vector graphics (SVG) for each top gate and paged gate at each value of time.

$ pip3 install pfta 

• If simply using as a command line tool, do pipx instead of pip3 to avoid having to set up a virtual environment.
• If using Windows, do pip instead of pip3.

$ pfta [-h] [-v] ft.txt Perform a fault tree analysis. positional arguments: ft.txt fault tree text file; output is written to `{ft.txt}.out/` options: -h, --help show this help message and exit -v, --version show program's version number and exit 

from pfta.core import FaultTree fault_tree = FaultTree(''' - times: nan  Event: A - model_type: Fixed - probability: 0 - intensity: 0.9  Event: B - model_type: Fixed - probability: 0.7 - intensity: 0  Event: C - model_type: Fixed - probability: 0 - intensity: 1e-4  Gate: AB - type: AND - inputs: A, B  Gate: AB_OR_C - type: OR - inputs: AB, C ''') fault_tree.gates[0] # Gate(id_='AB', is_paged=False, type_=<GateType.AND: 2>, vote_threshold=None, input_ids=['A', 'B'], is_top_gate=False, flattened_indexer=FlattenedIndexer(time_count=1, sample_size=1, flattened_size=1), computed_expression=<...>, computed_probabilities=<...>, computed_intensities=<...>, computed_rates=<...>) fault_tree.gates[0].computed_rates # [0.63] fault_tree.gates[1] # Gate(id_='AB_OR_C', is_paged=False, type_=<GateType.OR: 1>, vote_threshold=None, input_ids=['AB', 'C'], is_top_gate=True, flattened_indexer=FlattenedIndexer(time_count=1, sample_size=1, flattened_size=1), computed_expression=<...>, computed_probabilities=<...>, computed_intensities=<...>, computed_rates=<...>) fault_tree.gates[1].computed_rates # [0.6301]

Copyright 2025 Conway.
Licensed under the GNU General Public License v3.0 (GPL-3.0-only).
This is free software with NO WARRANTY etc. etc., see LICENSE.