feat(iace): open-source safety KB sources + bp_iace_safety_kb (Thema 2)
Versioned, license-tagged source docs for the multi-layer GT knowledge base, ingested into the new core RAG collection bp_iace_safety_kb (whitelisted in the RAG search handler): - prism_risk_methodology.md — OPSS PRISM v2 (OGL v3): full severity(4)× probability(8) → risk-level matrix (Serious/High/Medium/Low), RAPEX-aligned. - cobot_biomech_limits.md — CC BY 4.0 papers (Behrens 2022 / Park 2019): force (N) & pressure (N/cm²) pain thresholds by body region (the data behind ISO/TS 15066, cited from the open papers — standard tables NOT reproduced). - hse_example_risk_assessments.md — HSE (OGL v3): qualitative hazard→control. - osha_robot_safety.md — OSHA OTM (public domain): 250 mm/s teach anchor, robot hazard taxonomy, safeguarding hierarchy. No DIN/EN/ISO/IEC/DGUV content reproduced; each doc states its license + attribution. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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# PRISM — Product Safety Risk Assessment Methodology (severity × probability matrix)
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Canonical, citable source document for the IACE severity/probability risk-matrix
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anchors. PRISM gives a complete, openly-licensed severity-of-harm × probability
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risk-rating method that maps directly onto the IACE S (severity) and W
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(frequency/probability) tiers and the four-level risk output.
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## Source
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- **Source:** UK Office for Product Safety & Standards (OPSS), Dept. for Business & Trade
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- **Doc:** Product Safety Risk Assessment Methodology (PRISM), *A Guide for GB Market Surveillance Authorities*, Version 2.0, October 2024 (52 pp.)
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- **License:** Open Government Licence v3.0 (OGL v3) — reuse permitted with attribution
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- **Attribution:** `Source: OPSS, PRISM v2.0 (Oct 2024), © Crown copyright, licensed under the Open Government Licence v3.0`
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- **Retrieved:** 2026-06
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- **URL (guidance):** https://www.gov.uk/guidance/product-safety-risk-assessment-methodology-prism
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- **URL (PDF):** https://assets.publishing.service.gov.uk/media/66fd385ae84ae1fd8592ec93/prism-guidance-v02.pdf
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**Safety Gate / RAPEX alignment:** PRISM is the GB revision of the EU Safety Gate
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(RAPEX) risk-assessment guidance (Commission Implementing Decision (EU) 2019/417).
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It retains the same severity×probability structure and the same four resulting
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risk levels (Serious / High / Medium / Low), so the matrix below is broadly
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interoperable with the EU Safety Gate methodology.
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## Risk-assessment model
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Risk = f(severity of harm, probability of harm). The assessor builds one or more
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**harm scenarios** (3–5 steps: hazard exists → exposure occurs → exposure causes
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harm), then determines (v) severity and (vi) probability and reads off the risk
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level. The four output risk levels are **Serious, High, Medium, Low**.
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### Severity-of-harm levels (PRISM Table 2)
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Four levels, by reversibility and treatment required. (Descriptions distilled; the
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standard's full clinical example lists are not reproduced.)
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| Level | Description (severity of harm) |
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|---|---|
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| 1 | Minor: after basic first aid does not substantially hamper functioning or cause excessive pain; consequences usually fully reversible. |
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| 2 | Moderate: A&E visit may be needed, hospitalisation generally not; functioning affected for a limited period (≤ ~6 months), recovery more or less complete. |
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| 3 | Serious: normally requires hospitalisation; affects functioning for > 6 months or causes permanent loss of function. |
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| 4 | Critical/fatal: is or could be fatal (incl. brain death); reproductive harm; severe loss of limbs/function (> ~10% disability). |
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Each level also carries a "potential for multiple casualties?" (Yes/No) flag.
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### Probability-of-harm bands (PRISM Table 3, row axis)
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Probability that the harm scenario materialises over the product lifetime, in
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eight bands. Per-step probabilities are multiplied to give the overall figure.
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| Band | Probability over product lifetime |
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|---|---|
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| 1 | > 50 % |
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| 2 | > 1 in 10 |
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| 3 | > 1 in 100 |
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| 4 | > 1 in 1,000 |
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| 5 | > 1 in 10,000 |
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| 6 | > 1 in 100,000 |
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| 7 | > 1 in 1,000,000 |
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| 8 | < 1 in 1,000,000 |
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### Risk matrix — single item (PRISM Table 3)
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Severity (column) × probability (row) → risk level.
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| Probability ↓ \ Severity → | Level 1 | Level 2 | Level 3 | Level 4 |
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|---|---|---|---|---|
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| > 50 % | High | Serious | Serious | Serious |
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| > 1 in 10 | Medium | Serious | Serious | Serious |
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| > 1 in 100 | Medium | Serious | Serious | Serious |
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| > 1 in 1,000 | Low | High | Serious | Serious |
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| > 1 in 10,000 | Low | Medium | High | Serious |
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| > 1 in 100,000| Low | Low | Medium | High |
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| > 1 in 1,000,000 | Low | Low | Low | Medium |
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| < 1 in 1,000,000 | Low | Low | Low | Low |
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### Population escalation — all items in use (PRISM Table 4)
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Single-item risk can escalate by the number of items in the field (population risk).
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| Items in use ↓ \ single-item risk → | Low | Medium | High | Serious |
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|---|---|---|---|---|
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| > 1m | High | Serious | Serious | Serious |
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| > 500k | Medium | High | Serious | Serious |
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| > 100k | Medium | High | High | Serious |
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| ≤ 100k | Low | Medium | High | Serious |
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(For ≤ 100k the mapping is constant: Low→Low, Medium→Medium, High→High, Serious→Serious.)
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After rating, the assessor records an **uncertainty level** (low/medium/high) and
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may run a sensitivity analysis by varying severity, probability or item count.
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## How these are used in IACE
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1. **Tier definition (S × W):** the four severity levels map to the IACE **S**
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(severity) tiers and the eight probability bands map to the IACE **W**
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(frequency/probability) tiers, giving a defensible, openly-licensed scale.
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2. **Risk lookup:** Table 3 anchors the severity×probability → risk-level lookup
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in `risk_estimation.go`; the four outputs (Serious/High/Medium/Low) align the
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IACE risk categories with the EU Safety Gate scale.
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3. **Population escalation:** Table 4 provides the pattern for scaling
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single-instance risk by exposure/population where IACE has fleet/installed-base
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counts.
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4. **Uncertainty:** PRISM's low/medium/high uncertainty + sensitivity-analysis
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step backs the IACE confidence flag on each estimate.
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No DIN/EN/ISO/IEC risk-graph, decision tree or SIL/PL table is reproduced; the
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matrix above is the OGL-v3 PRISM/Safety-Gate matrix only.
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