🧰 Thermal Runaway
The self-feeding reaction inside a damaged or overcharged lithium cell where heat generates more heat until the pack vents, burns fiercely, and can reignite later.
Warning signs are swelling, hissing, rapid heating or a sweet chemical smell — stop charging, move people away, and let a burning pack burn out on a non-flammable surface while you call emergency services. Never seal a hot or venting pack in an airtight container, and never carry it.
What it actually does
Thermal runaway is the chain reaction where a damaged lithium cell heats up, and that heat causes more of the reaction that produces it, and so on. It is the reason all the LiPo handling rules exist. It is rare and entirely avoidable, but it is why nobody in the hobby treats charging casually.
In practice
Prevention is the whole game: charge at a sensible rate with the right cell count set, balance charge, never charge a pack that is hot, damaged, punctured or puffed, use a charging bag or metal container, charge on a non-flammable surface, and stay in the room. Let packs cool to room temperature after a run before charging.
Worth knowing
If a pack starts to swell rapidly, hiss, or give off smoke or a sharp smell, treat it as an emergency. Get people away from it, do not breathe the fumes, and call the fire service — do not try to carry a pack that is already venting.