Prerequisites
Before rating SEC parameters, ensure you have:
- Created a HARA document with the HARA risksheet template
- Identified hazards with complete operational situation descriptions
- Access to ISO 26262-3 Tables 1-4 (severity/exposure/controllability definitions)
Rate Severity (S0-S3)
- Open your HARA document in Polarion
- Switch to the HARA Classification view in the risksheet
- For each hazard row, click the Severity column dropdown
- Select the appropriate S-rating based on potential harm:
| Rating | Definition | Example |
|---|
| S0 | No injuries | Nuisance warning light activation |
| S1 | Light/moderate injuries | Minor whiplash from delayed braking |
| S2 | Severe/life-threatening injuries | Collision with pedestrian at low speed |
| S3 | Life-threatening/fatal injuries | High-speed collision, loss of steering control |
Focus on the worst credible harm to occupants or other road users, not the most likely outcome. Consider vulnerable road users (pedestrians, cyclists) as well as vehicle occupants.
Rate Exposure (E0-E4)
- In the same risksheet row, click the Exposure column dropdown
- Rate based on how frequently the operational situation occurs:
| Rating | Definition | Example |
|---|
| E0 | Incredible | Specific sensor failure + rare weather + specific road geometry |
| E1 | Very low probability | Extreme environmental conditions (heavy fog + night + rain) |
| E2 | Low probability | Occasional driving scenarios (parking maneuvers) |
| E3 | Medium probability | Frequent scenarios (highway cruise, urban traffic) |
| E4 | High probability | Continuous operation (vehicle speed monitoring, brake availability) |
Rate how often the operational situation occurs during vehicle lifetime, not how often the hazard manifests. A failure mode may be rare, but if it affects a continuous operation (E4), exposure is high.
Rate Controllability (C0-C3)
- Click the Controllability column dropdown for each hazard
- Rate based on the average driver’s ability to prevent harm:
| Rating | Definition | Driver Control % | Example |
|---|
| C0 | Controllable in general | 100% | ABS warning light (no performance impact) |
| C1 | Simply controllable | >99% | Gradual brake fade with warning |
| C2 | Normally controllable | >90% | Single sensor loss with degraded AEB performance |
| C3 | Difficult/uncontrollable | <90% | Total brake failure at highway speed |
- Reaction time available: Seconds or milliseconds?
- Driver awareness: Is there a warning before hazardous event?
- Required skill level: Can an average driver respond effectively?
- Physical demands: Does control require extreme force or precision?
Verify ASIL Calculation
After rating all three parameters, the risksheet automatically computes ASIL:
ASIL = lookup_matrix(Severity, Exposure, Controllability)
E1 E2 E3 E4
S1 C1 QM QM QM A
C2 QM QM A B
C3 QM A B C
S2 C1 QM QM A B
C2 QM A B C
C3 A B C D
S3 C1 QM A B C
C2 A B C D
C3 B C D D
If Controllability = C0 (controllable in general) or Exposure = E0 (incredible), the ASIL is automatically QM (Quality Management) regardless of severity. No safety goals are required.
Document Rationale
- Click the hazard row to open the work item form
- Scroll to the HARA Rationale text field
- Document your reasoning for each S/E/C rating:
- Reference ISO 26262 table definitions
- Cite analysis data (e.g., operational frequency statistics)
- Note assumptions (e.g., “assumes average driver with valid license”)
- Reference expert judgement or safety workshops
Example Rationale:
S3: Total loss of braking at highway speed (>100 km/h) is
life-threatening per ISO 26262-3 Table 1.
E4: Highway driving represents >40% of total vehicle operating time
(source: usage profile study, Doc-AEB-2025-01).
C3: Emergency stop from 100 km/h with zero brake force is uncontrollable
by average driver. No alternative braking method available.
ASIL D assigned per ISO 26262-3 Table 4 (S3-E4-C3).
ASCII Workflow Diagram
Verification Steps
You should now see:
- All hazards with S/E/C ratings assigned (no empty cells in HARA Classification view)
- ASIL values automatically computed for each hazard
- Rationale field populated for each hazard with audit-trail justification
- High ASIL values (C/D) highlighted if traffic light decorators are configured
The risksheet should display color-coded cells (green for low risk, red for C3/S3) if cell decorators are enabled in the HARA Risksheet Configuration.
Common Pitfalls
Exposure rates the operational situation frequency, not how often the component fails. A rare failure mode (1 in 10⁶ hours) affecting continuous operation still gets E4 if the operation runs continuously.
Use the >99% / >90% driver control thresholds from ISO 26262-3 Table 3. Don’t assume expert drivers or ideal conditions (dry road, daylight, full attention).
See Also
