The Tesla Model S battery has been reactivated twice after the crash, according to the NTSB

According to a new report by federal investigators, a Tesla battery caught fire twice after being involved in an accident. But given the volatile nature of lithium-ion batteries, perhaps that should not have been a surprise.

The National Transportation Safety Board (NTSB) today released a preliminary report on a Tesla Model S that crashed in Florida, killing two people and injuring one. The report says that after extinguishing a fire that consumed the vehicle, the battery caught fire once again being charged to be removed from the scene. The battery caught fire again when he arrived at the storage yard. Both times the fire was extinguished.

This is not the first time that a Tesla battery has been relighted following a collision. It's also happened after a Tesla Model X crash earlier this year in California, which is still under investigation by the NTSB. While this may stir up fear among those unfamiliar with electric vehicles, reappearance is not only feasible, but it is something that needs to be watched by all concerned.

The delicate dance: lithium-ion batteries and heat

Lithium-ion fires can occur for a variety of reasons, but most of them boil down to heat. EV batteries contain thousands of individual cells, and if a battery is punctured, lithium reacts violently with water in the air, generating a lot of heat and sometimes a fire. If you have ever seen a YouTube video of a person stabbing a phone battery, that is what happens – air enters, reacts with lithium and lights a fire.

That is why the batteries contain precautions to avoid the thermal runaway – the swollen batteries are the battery doing its best to keep these items from being exposed to the air even though the battery has already failed but not yet ignited.

The charging and discharging cycles of lithium-ion batteries also generate heat, which is why EV batteries have serious cooling systems – again, to prevent this heat from creating greater problems. It is a delicate dance between loading, unloading and attenuation of heat produced.

Why this should not stir up anti-EV sentiments

That brings us back to Tesla's battery. According to the Model S emergency response guide, Tesla suggests that the responders "plan to let the battery burn while protecting the exposures." To let the fire consume the whole battery means all that lithium reacts and finally stops burning.

But if a fire department arrives and turns off the battery at the place where the fire appears to stop, he might not have stopped completely. Tesla batteries contain many firewalls to slow the spread of fire and (hopefully) allow people to be as far away as possible, as quickly as possible. But these firewalls also have the side effect of making a fire appear done when he might not be.

It is possible that the fire department or the operator of the tow truck responsible for the transportation did not check the continuous exothermic reaction of the battery with a thermal camera – something that Tesla explicitly recommends to do after fire – so that heat continues to accumulate in the battery until a set of unburned cells jumped and caught fire. And that 's probably what happened when the fire ignited again in the storage yard. The NTSB report does not say what the fire department and the tow truck operator put up after the fire that followed the accident.

Always treat a weapon as if it were loaded, even if it is not the case; Always treat a damaged lithium-ion battery as an immediate fire hazard, even if the fire is apparently extinguished.

Tracking lights: not the first time

The federal government also has experience in lithium-ion battery fires. After testing the new Chevrolet Volt in 2011, the National Road Safety Authority discovered that the Volt tested had caught fire after the fact. He had similar problems in subsequent lab tests intended to replicate the original conditions.

Eventually, the case was closed. It turns out that the Volt's battery caught fire because the NHTSA crash test compromised the battery, which was not discharged even though GM's emergency policy suggested unloading the battery after an accident. The relevant battery was then subjected to rollover tests, which caused the coolant to leak from a salvage line. Later, when the accidental volt was stored outside, the coolant crystallized, causing the short that triggered the fire.

It just shows that, whatever the degree of control of an environment, these batteries that are in everything from our phones to our cars, must be treated with the utmost care.

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