AIS 156 Phase 2: How thermal propagation actually works

What Phase 2 actually requires

The Phase 2 thermal propagation test isn't just "does the pack catch fire." It's a series of measurements: how long the pack contains a single forced cell failure before any external sign of fire, smoke, or rupture. Phase 1 required containment for a few minutes. Phase 2 stricter containment thresholds reflect what actually matters in a real-world thermal event: time for occupants to react.

Why labs interpret it differently

There are five ARAI-approved labs in India running AIS 156 P2. We've sent the same SKU to three of them for cross-checking. The variance in the timing measurements was meaningful. The standard specifies the methodology, but interpretation of "first external sign" varies — is it visible smoke? Audible venting? A 5°C surface temperature rise on the casing?

What this means for procurement

If your supplier says "we passed AIS 156 P2," ask which lab and ask for the actual report. The cert number alone doesn't tell you how well the pack performed — only that it crossed the minimum threshold.

How Kinetra packs handle it

Our LFP packs (K-2W and K-3W series) contain the failure for an average of 12 minutes across the three labs we've tested at — well above the standard's threshold. We achieve this through three design choices: cell-to-cell thermal barriers (mica + intumescent), distributed pressure relief, and BMS-triggered isolation when a cell exceeds its rated max temperature.

What to ask your supplier

1. Which ARAI lab issued the certificate?
2. What was the actual containment time recorded?
3. What is the design philosophy — passive containment, active isolation, or hybrid?
4. How does the BMS detect propagation onset?

If you don't get clean answers to these, you're not getting a real engineering supplier — you're getting a paper supplier.