Thermal propagation — deep dive¶
What is this: the in-depth explainer for clause 5.2.7 b), clause 8.2.7.2, and Appendix C of GB 38031-2025 — the rule that a single-cell thermal runaway must not become a pack fire, must trigger an alarm within 5 minutes, and must not endanger the cabin with smoke.
This is not the procedural test page — for that, see Thermal propagation (8.2.7.2). These pages explain the why and the underlying mechanisms.
The headline rule¶
"After thermal runaway caused by internal short-circuiting of a single cell, the battery pack or system should not catch fire or explode. It should provide a thermal event alarm signal no later than 5 minutes after the thermal runaway occurs. Additionally, within 5 minutes before and after the thermal event alarm signal is issued, the smoke should not pose a danger to the occupant compartment." (C.1)
Three separate conditions, all must be satisfied:
- No fire, no explosion at pack/system level after a single-cell TR.
- Thermal event warning ≤ 5 min after TR is triggered in that cell.
- Smoke condition in the 10-minute window centred on the warning — at pack/system level, by documentation; at vehicle level, by observation that smoke does not enter the cabin.
Map of this deep dive¶
| Page | What it covers |
|---|---|
| Why this matters | The risk model: why single-cell TR is the scenario the standard targets, and what the 2025 revision changed |
| OEM documentation package | The three-report structure (Table C.1) the manufacturer must submit |
| Monitoring and sensors | Where to put voltage / temperature sensors (C.5.3.6) for each trigger method |
| Runaway confirmation | The (a OR b) AND c rule — what counts as TR having occurred |
| Smoke and the passenger compartment | The 5-min warning rule and the cabin-smoke conditions, pack vs. vehicle level |
| Trigger methods | Overview of the three recommended trigger methods |
| → Needle penetration | C.5.3.3 |
| → External heating | C.5.3.4 |
| → Internal heating plate | C.5.3.5 |
How the pieces fit¶
The OEM submits three reports (Table C.1). The third is a verification test report. The verification test follows the procedure in C.5: choose a trigger cell near the centre of the pack, apply one of the three recommended trigger methods, monitor cell voltage and temperature at < 1 s sampling, and confirm TR using the (a OR b) AND c rule. Once TR is triggered, the 5-minute warning clock starts, and the test continues until all monitor points are ≤ 60 °C (minimum 2 h).
A pass means: TR happened in the trigger cell, but the rest of the pack survived; the warning signal reached the driver in time; no fire, no explosion; and smoke did not endanger the cabin.
Source: GB 38031-2025, clause 5.2.7 b) (PDF p. 12), clause 8.2.7.2 (PDF p. 24), and Appendix C in full (PDF p. 26, 34–38).