Overview
The HARA severity enumeration implements the four-level severity classification from ISO 26262-3:2018 Table 5, establishing a standardized scale for assessing potential harm to vehicle occupants and other road users. Severity is purely outcome-focused: it classifies what injury could result from a hazardous event, independent of how often the event occurs or whether it can be controlled.
| Severity Level | Injury Outcome | ASIL Impact | Use Case |
|---|
| S0 | No injuries | QM (no safety requirement) | Hazards causing no harm; quality management only |
| S1 | Light/moderate injuries | Typically ASIL A or B | Recoverable injuries; minor safety concern |
| S2 | Severe injuries (survival probable) | Typically ASIL B or C | Serious injuries requiring robust safety mechanisms |
| S3 | Life-threatening or fatal injuries | Typically ASIL C or D | Maximum safety concern; highest integrity required |
Severity is one dimension of the three-dimensional ASIL matrix (Severity × Exposure × Controllability). While severity describes the worst-case harm, exposure and controllability determine how likely the hazard is to occur and whether drivers can prevent it. Together, all three determine the ASIL classification.
Severity Levels Reference
S0 – No Injuries
Definition: Hazardous events that result in no injuries to vehicle occupants or other road users.
| Property | Value |
|---|
| Label | S0 |
| Numeric Value | 0 |
| ISO 26262 Reference | ISO 26262-3:2018 Table 5 |
| Injury Outcome | No harm to any person |
| ASIL Classification | QM (Quality Management) |
| Typical Examples | Minor cosmetic damage, non-functional component failure with no safety impact |
S1 – Light/Moderate Injuries
Definition: Hazardous events that may cause light to moderate injuries, typically recoverable without permanent disability.
| Property | Value |
|---|
| Label | S1 |
| Numeric Value | 1 |
| ISO 26262 Reference | ISO 26262-3:2018 Table 5 |
| Injury Outcome | Light to moderate injuries; full recovery expected |
| ASIL Classification | Typically ASIL A or B (depending on E and C) |
| Typical Examples | Minor lacerations, temporary loss of consciousness, minor whiplash injuries |
- S1 + E1–E2 + C0–C1 → ASIL A
- S1 + E3–E4 + C1–C2 → ASIL B
- S1 + E0 + any C → QM
S2 – Severe Injuries (Survival Probable)
Definition: Hazardous events that may cause severe injuries where survival is probable but permanent disability or long-term medical treatment is likely.
| Property | Value |
|---|
| Label | S2 |
| Numeric Value | 2 |
| ISO 26262 Reference | ISO 26262-3:2018 Table 5 |
| Injury Outcome | Severe injuries; survival likely but permanent effects possible |
| ASIL Classification | Typically ASIL B or C (depending on E and C) |
| Typical Examples | Broken bones, head trauma with recovery, severe burns, permanent partial disability |
- S2 + E1–E2 + C0–C1 → ASIL B
- S2 + E3–E4 + C1–C2 → ASIL C
- S2 + E0 or low E/high C → ASIL A or B
S3 – Life-Threatening or Fatal Injuries
Definition: Hazardous events with the potential to cause life-threatening or fatal injuries to vehicle occupants or other road users.
| Property | Value |
|---|
| Label | S3 |
| Numeric Value | 3 |
| ISO 26262 Reference | ISO 26262-3:2018 Table 5 |
| Injury Outcome | Life-threatening or fatal; multiple fatalities possible |
| ASIL Classification | Typically ASIL C or D (almost always D for high E/C) |
| Typical Examples | Head-on collision at highway speed, complete brake failure, total loss of steering control |
- S3 + E3–E4 + C1–C3 → ASIL D
- S3 + E1–E2 + any C → ASIL C or D
- S3 + E0 → ASIL A, B, or C (very rare scenario)
Critical Note: S3 hazards require the highest level of safety design effort, including:
- Comprehensive safety mechanisms and redundancy
- Extensive verification and validation
- Failure Mode and Effects Analysis (FMEA) decomposition
- Risk control measures with pre- and post-mitigation ratings
- Complete traceability from safety goals through implementation
ASIL Severity Impact
The following table shows how Severity combines with representative Exposure and Controllability values to determine ASIL:
| Severity \ Probability | P1 (Incredible) | P2 (Very Low) | P3 (Low) | P4 (Medium) | P5 (High) |
|---|
| S1 (Minor) | QM | QM | QM | ASIL A | ASIL A |
| S2 (Moderate) | QM | QM | ASIL A | ASIL B | ASIL B |
| S3 (Severe) | QM | ASIL A | ASIL B | ASIL C | ASIL C |
| S4 (Life-Threatening) | ASIL A | ASIL B | ASIL C | ASIL D | ASIL D |
Severity Assessment Guidelines
When conducting HARA, use the following criteria to assign severity:
Injury Classification Criteria
S0 (No Injuries):
- No harm to any person
- Only property damage or functional degradation
- Quality issues, not safety issues
S1 (Light/Moderate):
- Injuries from which recovery is expected
- Temporary incapacity (hours to days)
- Minor permanent effects
- Examples: whiplash, minor lacerations, temporary unconsciousness
S2 (Severe, Survival Probable):
- Serious injuries with significant disability or long-term medical treatment
- Permanent partial disability possible
- Long-term incapacity (weeks to months of treatment)
- Examples: fractured limbs, head trauma with recovery, severe burns
S3 (Life-Threatening/Fatal):
- Immediate threat to life
- Fatality possible
- Multiple fatalities in mass-casualty scenarios
- Permanent total disability or immediate death
- Examples: head trauma without recovery, high-speed collision, asphyxiation
Context Considerations
Severity assessment should account for:
- Occupant Type: Distinguish between vehicle occupants (driver, passengers) and vulnerable road users (pedestrians, cyclists)
- Impact Zone: Head/thorax injuries typically higher severity than limb injuries
- Impact Speed: Higher speed impacts correlate to higher severity potential
- Age Factor: Pediatric and elderly occupants may experience greater injury severity from same impact
- Pre-existing Conditions: Consider whether underlying health factors increase severity (not typically part of HARA but noted in risk context)
Severity is outcome-focused and independent of how often the hazardous event occurs. A rare but catastrophic event (S3, E1) may be assigned higher ASIL than a frequent minor event (S1, E4, C0) depending on Controllability. Do not conflate severity with exposure or likelihood.
Risksheet Integration
Column Binding
In the TestAuto2 solution, severity is exposed in Risksheet configurations through a dropdown column bound to the haraServerity custom field on Hazard work items:
# HARA Risksheet Column Definition
- name: severity
label: Severity (S)
type: enum
field: haraServerity
width: 80px
level: 4 # Hazard level
alignment: center
// Pseudocode: ASIL Calculation Formula
function calcASIL(severity, exposure, controllability) {
const sevNum = extractNumeric(severity); // S0→0, S1→1, S2→2, S3→3
const expNum = extractNumeric(exposure); // E0→0, E1→1, ..., E4→4
const conNum = extractNumeric(controllability); // C0→0, C1→1, ..., C3→3
if (sevNum === 0 || expNum === 0 || conNum === 0) {
return "QM"; // S0, E0, or C0 always yields QM
}
return lookupASILMatrix(sevNum, expNum, conNum); // 1-3 → A-D
}
Cell Styling
Severity cells in Risksheet are styled with conditional formatting to highlight high-risk classifications:
| Severity | CSS Class | Background Color | Purpose |
|---|
| S0 | severity-s0 | Light gray | Low severity; QM only |
| S1 | severity-s1 | Light green | Minor safety concern |
| S2 | severity-s2 | Orange | Significant safety concern |
| S3 | severity-s3 | Red/Dark red | Critical safety concern |
S2 and S3 hazards are visually emphasized in Risksheet to help teams prioritize risk mitigation efforts. Color-coded cells support rapid identification of high-severity hazards requiring immediate attention.
Severity Inheritance and Traceability
Safety Goal Propagation
When a Hazard work item with assigned Severity is linked to a Safety Goal via the derivedFrom relationship, the Safety Goal inherits the Severity classification:
This traceability chain ensures that functional safety requirements derived from high-severity hazards are appropriately scoped and prioritized.
FMEA Cross-Reference
Severity is also correlated with FMEA Severity ratings (1–10) used in Failure Mode and Effects Analysis. While HARA Severity (S0–S3) is qualitative and automotive-focused, FMEA Severity (1–10) is quantitative and process-focused. The correlation helps ensure consistency across risk management disciplines:
- HARA S0 ↔ FMEA Severity 1–2 (minimal/no impact)
- HARA S1 ↔ FMEA Severity 3–5 (moderate impact)
- HARA S2 ↔ FMEA Severity 6–8 (severe impact)
- HARA S3 ↔ FMEA Severity 9–10 (catastrophic impact)
See reference/enumerations/fmea-severity.md for FMEA severity details.
Standards Compliance
This enumeration directly implements:
- ISO 26262-3:2018, Table 5 — Severity classification for Hazard Analysis and Risk Assessment
- ISO 26262-3:2018, Clause 7.4.3 — Hazard classification methodology
- ISO 26262 Part 3, Annex B — Guidance on severity assessment
The four-level scale (S0–S3) is mandatory for ISO 26262 HARA compliance and forms the normative basis for ASIL determination across all Functional Safety products.
