format_version: "0.1"
id: fbd_fan_damper
name: "Fan and damper permissive (FBD)"
domain: hvac
language: FBD
source:
  origin: authored
  reference: "Supply air handler permissive, authored for FBD language coverage"
  license: CC-BY-4.0
properties_file: props.yaml
safety_intent: "The fan must never run against a shut damper, and a duct smoke alarm must drop the fan."
validation_status: candidate
variants:
  - file: clean.xml
    expected_verdict: true
    ground_truth:
      method: expert
  - file: bomb.xml
    expected_verdict: false
    violated_properties: [P1]
    ground_truth:
      method: fault-injection
      base_variant: clean.xml
      seeded_defect: "The damper_open wire into the AND block was deleted, leaving fan := fan_cmd AND NOT smoke."
      witness: "fan_cmd=1, damper_open=0, smoke=0 drives fan=1 with the damper shut."
metrics:
  pous: 1
  blocks: 2
  variables: 4
features: [blocks, permissive, negated_input]
difficulty: easy
tags: [safety, interlock, language-coverage]