Smoke and the passenger compartment¶
What is this: the 5-minute warning rule and the smoke-safety conditions in clause 5.2.7 b) — what they require, how they differ between pack/system and vehicle level, and where they sit in the test timeline.
The 5-minute warning rule¶
"Provide a thermal event warning signal, and the warning signal should be sent no later than 5 minutes after thermal runaway of the battery cell is triggered." (5.2.7 b) 2)
Reading this precisely:
- The clock starts at TR triggered — i.e. the moment the trigger device (needle, heater) starts being applied. Not the moment TR is confirmed under C.5.3.7's (a OR b) AND c rule.
- The warning signal is the manufacturer-defined alarm signal described in Report 1 of the OEM documentation package (C.2).
- 5 minutes is the upper limit, not a target. Tighter is fine.
The smoke clauses¶
The smoke condition is in 5.2.7 b) 3) and is restated in C.1 and C.3.5 e). It is enforced two different ways depending on whether the test object is the pack/system alone or the entire vehicle.
Pack/system level — documentation requirement¶
"For battery pack or system-level testing, provide technical documentation indicating that smoke does not pose a danger to the passenger compartment within 5 minutes before and after the thermal event warning signal is issued." (5.2.7 b) 3)
This is a paper requirement, lodged inside Report 2 of the OEM documentation package:
"If the manufacturer uses the battery pack or system as the test object in C.5, the technical documentation of the risk mitigation function should include a description that, before the thermal event alarm signal is issued and within 5 minutes after the alarm signal is issued, the smoke does not pose a danger to the occupant compartment." (C.3.5 e)
The OEM reasons about pack vent paths, the as-installed orientation, and how smoke would propagate from the pack under the vehicle to the cabin HVAC inlets, and shows that this trajectory is not a danger in the relevant 10-minute window.
Vehicle level — observed fact¶
"...for vehicle-level testing, smoke should not enter the passenger compartment within 5 minutes before and after the thermal event warning signal is issued." (5.2.7 b) 3)
At vehicle level, the documentation is not enough — the test agency observes whether smoke actually enters the cabin. The standard requires in-cabin video capture for this purpose:
"For vehicle-level testing, the vehicle's dashboard and central control screen should display normally with no warning messages. Video capture devices should be set up inside the passenger compartment to ensure the interior space can be observed in real-time. The vehicle should adopt the control strategy used during the 1-hour power-down state, with the vehicle in park mode, doors, windows, and sunroof closed, and air conditioning off." (C.5.2 d)
Closed cabin, A/C off, doors and windows shut. Smoke ingress in this state during the 10-minute window is a fail.
The 10-minute window¶
The smoke condition is "5 minutes before and 5 minutes after the warning signal." The warning may come up to 5 minutes after TR is triggered. So the smoke window can extend up to roughly:
| Event | Earliest | Latest |
|---|---|---|
| TR triggered | t = 0 | t = 0 |
| Warning signal issued | t = 0 (immediate) | t = +5 min |
| Smoke window starts | t = −5 min (i.e. 5 min before warning, which can be before TR trigger) | t = 0 |
| Smoke window ends | t = +5 min | t = +10 min |
The "5 minutes before" half is interesting because it can extend back before TR was triggered — i.e. during the trigger application itself. In practice trigger-method smoke (from heater materials, needle lubricant) needs to be controlled so it does not show up in this window and confuse the assessment.
Summary table¶
| Condition | Pack / system level | Vehicle level |
|---|---|---|
| Warning ≤ 5 min after TR trigger | yes | yes |
| Smoke condition | OEM documentation: smoke does not endanger cabin in 10-min window | Observed: smoke does not enter cabin in 10-min window |
| Cabin video required | no | yes (C.5.2 d) |
| No fire / no explosion | yes | yes |
Engineering note (non-normative): The "5 minutes before warning" half of the window is awkward at vehicle level because it includes time when the trigger is still being applied. For external heating the heater can produce visible thermal effects (off-gassing of cover materials) before the cell itself runs away. Plan the test rig so that trigger-device emissions are isolated from the vehicle (e.g. routed away from the underbody) — otherwise harmless trigger smoke can fail the test.
Engineering note (non-normative): The pack/system documentation case (C.3.5 e) is sometimes treated as a soft requirement because no agency observes the smoke trajectory directly. It is not soft. The technical documentation must be defensible — typically with CFD or empirical pack-venting data — and the test agency can challenge it. Treat C.3.5 e) as you would any other safety-case argument.
Cross-references¶
- OEM documentation package — where C.3.5 e) lives
- Runaway confirmation — what "TR triggered" formally means
- Why this matters — the regulatory rationale for the smoke condition
Source: GB 38031-2025, clause 5.2.7 b) (PDF p. 12), Appendix C section C.1 and C.3.5 e) and C.5.2 d) (PDF p. 34–35).