safety-shield 0.1.0

S-ARPN: Physical safety scoring as a continuous constraint on strategic decision systems

Safety Shield

S-ARPN: Physical safety scoring for threat assessment and protective measure planning.

Safety Shield quantifies physical safety threats using S-ARPN (Safety-Adapted Risk Priority Number), a five-dimension scoring system. It also includes ARPN (Adjusted Risk Priority Number) for litigation risk scoring. Both derive from FMEA (Failure Mode and Effects Analysis) methodology adapted from aerospace and manufacturing.

Who This Is For

• Anyone facing physical threats where strategic decisions (legal filings, regulatory complaints, negotiations) affect safety
• Whistleblowers facing retaliation
• Attorneys assessing client safety risk in adversarial proceedings
• Advocates and case workers managing threat situations
• Co-founder disputes, employment retaliation, or any scenario where business conflict has a safety dimension

S-ARPN Scoring

S-ARPN = TS x P x V x BI x EC

Dimension	Scale	Definition
TS (Threat Severity)	1-10	Worst-case physical outcome. 7=injury, 9=life-threatening, 10=lethal.
P (Probability)	1-10	Likelihood given current conditions.
V (Vulnerability)	1-10	Target exposure. Protective measures reduce V.
BI (Behavioral Impairment)	1.0-3.0	Substance use, violence history, impulse control. Clamped to 1.5 when P < 3 to prevent low-probability inflation.
EC (Escalation Coupling)	1-5	How many threat vectors activate simultaneously.

Maximum S-ARPN: 15,000

Tier Thresholds

Tier	S-ARPN	Required Response
IMMEDIATE	>3,000	Call 911. Leave location.
CRITICAL	1,500-3,000	LE report within 24 hours.
HIGH	500-1,500	Protective measures review.
MODERATE	100-500	Maintain awareness.
LOW	<100	Monitor.

ARPN Scoring (Litigation Risk)

ARPN = S x O x D x BA x CR

Dimension	Scale	Definition
S (Severity)	1-10	Case-level consequence if failure materializes.
O (Occurrence)	1-10	Probability of the failure mode.
D (Detectability)	1-10	How late we detect it (10 = no warning).
BA (Behavioral Amplifier)	0.5-2.0	Psychological distortion of rational play.
CR (Cascade Reach)	1-5	Cross-case impact.

Maximum ARPN: 10,000. Tiers: CRITICAL (>=2000), HIGH (>=1000), MODERATE (>=400), LOW (<400).

Includes MIL-STD-1629A Criticality Categories (Cat I through Cat IV).

Quick Start

pip install safety-shield

Score a threat

from safety_shield import compute_s_arpn, safety_tier

score = compute_s_arpn(ts=7, p=6, v=5, bi=2.0, ec=3)
tier = safety_tier(score)
print(f"S-ARPN: {score}  Tier: {tier}")
# S-ARPN: 1260.0  Tier: HIGH

Score litigation risk

from safety_shield import compute_arpn, arpn_tier

score = compute_arpn(s=7, o=7, d=3, ba=1.7, cr=3)
tier = arpn_tier(score)
print(f"ARPN: {score}  Tier: {tier}")
# ARPN: 749.7  Tier: MODERATE

CLI

# S-ARPN score
safety-shield score --ts 7 --p 6 --v 5 --bi 2.0 --ec 3

# ARPN score
safety-shield arpn --s 7 --o 7 --d 3 --ba 1.7 --cr 3

# Full assessment from YAML
safety-shield assess scenario.yaml

# Gap analysis: which protective measures reduce your score most
safety-shield analyze scenario.yaml

# Self-test
safety-shield selftest

Define a scenario in YAML

# scenario.yaml
threats:
  - id: ST-001
    description: "Coordinated intimidation campaign"
    ts: 7
    p: 6
    v: 5
    bi: 2.0
    ec: 3

protective_measures:
  - id: PM-001
    description: "LE report filed"
    status: done
    reduces_v: 0.1
    reduces_p: 0.15
    targets: [ST-001]

  - id: PM-002
    description: "Security cameras"
    status: not_started
    reduces_v: 0.15
    reduces_p: 0.1
    targets: [ST-001]

escalation_ladder:
  - level: 1
    description: "Verbal threats via proxy"
    observed: true
  - level: 2
    description: "Professional targeting"
    observed: false

Protective Measures

Each protective measure quantifiably reduces V (vulnerability) and/or P (probability) on specific threats. The gap analysis engine simulates applying each unimplemented measure and shows which ones reduce your S-ARPN the most.

safety-shield analyze scenario.yaml

GAP ANALYSIS: 1 unimplemented measures

  PM-002: Security cameras
    Impact on ST-001: S-ARPN 1071 -> 820 (-251)

Provenance

S-ARPN was developed by applying failure analysis methodologies from aerospace (MIL-STD-1629A), manufacturing, and fraud analytics to physical safety threats. The FMEA lineage spans hyperscale cloud infrastructure, manufacturing, NASA/FMECA, and fraud analytics.

Citation

@misc{mcnamara2026sarpn,
  author = {McNamara, Colin},
  title = {S-ARPN: Safety-Adapted Risk Priority Number for Physical Threat Assessment},
  year = {2026},
  publisher = {Colin McNamara LLC},
  howpublished = {\url{https://github.com/acquit-ai/safety-shield}}
}

Contributing

If you're in a situation where you need this tool, you're not alone. If you have expertise in threat assessment, safety advocacy, or safety engineering and want to improve the methodology, PRs are welcome.

License

MIT. See LICENSE.