Theory 12/Biot Number/Battery packs
Propagation Is a Biot Problem
The claim
Whether a failing cell ignites its neighbour is set by the neighbour's Biot number, so a well-cooled cell resists propagation even at close spacing.
01Mechanism
Heat arriving at the surface must be removed before it raises the core; the ratio determines whether the core reaches the trigger temperature.
02Prediction
Propagation should track Biot and spacing together.
03Refutation
Propagation tracking spacing alone would remove cooling.