Of course the likelihood of that device actually exploding is pretty small. "Something like 1 in 10 million," Ken Boyce, a battery expert and principal engineer director at UL, says. And as Boyce notes, there are currently billions of lithium batteries out there. Two decades of improvements by engineers and material scientists, assisted by safety science gurus like those at UL, have made the nearly ubiquitous lithium battery safer. Yet the fundamental nature of lithium batteries means the potential for a weenie roaster is always there.

That was a rude awakening for consumers back in 1995. Apple launched its Powerbook 5300 that year, and was one of the earliest adopters of lithium batteries. But when the Powerbook 5300 started catching on fire and a recall was launched, it cost the company millions and tech pundits started ringing the apocalypse bell. Fortunately the tech has now improved to the point that, when Apple batteries started swelling (and sometimes catching fire) in 2007, it was merely a cause for a quiet recall.

That's why the current Samsung Note7 fiasco is so fascinating. Following many, many explosions, the Note7 is the subject of a giant global recall. It's been banned by multiple airlines, and US officials have told people to turn of the phone and stop using it forever. It certainly isn't the first phone to go boom, but a confluence of new tech, and the inherent failings central to battery technology, improved the odds of Samsung's current firestorm.

Indeed, the central cause of the explosions isn't new. Heat is the enemy of the lithium battery. Heat degrades the battery's potential to hold a charge, which is why your phone runs down faster in the heat of the summer or when you use it for an extended period of time. And on rare occasions there can be too much heat. That's when you get thermal runaway.

"Thermal runaway is the technical term for the popular term of explosion," Professor Yang Shao-Horn, the WM Keck professor of energy at MIT, says with a chuckle. Then she clarified. "It's not actually an explosion, just a fire." Thermal runaway is a chemical reaction where heat grows exponentially — which isn't good when the chemicals getting heated rapidly, like those in a lithium battery, are also highly flammable.

Lithium batteries are nothing more than a mess of very flammable chemicals smooshed together and exposed to an electrical charge via electrodes. There are two primary electrodes in a lithium battery, the anode and the cathode (think the plus and minus sign on your AA battery). Energy goes in through the anode and out through the cathode and the two components are separated by an organic material that holds lithium salts — which is a fantastic element for efficient energy containment and transfer.

If the anode and the cathode experience contact with one another, then a thermal runaway can occur. Early lithium batteries were contained in flimsy looking bags which led to them easily being punctured, the anode and cathode touching each other, and the whole thing going poof. But later batteries aren't immune either.

In the video above, you see a standard lithium ion battery (18650) like those found in a vape or bundled together in the battery pack of a Tesla Model S. As soon as the nail punctures the battery, the anode and cathode touch and thermal runaway occurs.

The potential for explosion due to a puncture can be mitigated with better battery construction — which is why you generally don't have to worry about your Tesla Model S turning into charcoal after a car crash.

From what Samsung is currently reporting, the Note7's flaming failure was something akin to the above nail example. A failure in the production of a number of Note7 batteries meant undue pressure was being exerted on some of the battery packs, and in turn, increasing the likelihood that the anode and cathodes would come into contact.

It's a plausible conclusion, according to Shao-Horn. But she doesn't rule out another potential thermal runaway cause: Overcharging. That's when the positive electrode on the battery becomes so juiced up that it begins to create oxygen inside, which wrecks the delicately balanced chemical composition of the hermetically sealed battery and leads to thermal runaway.

"These processes can happen even in a perfect battery," Shao-Horn said, referring to overcharging and anode on cathode contact. Manufacturing defects like the ones reported in the Note7 failures and those linked to the explosions of cheap vapes, "only make these two processes much worse."

And they're not the only processes. Even a bad USB cable can harm your device. The charging process in a phone or laptop or vape is delicate, and the batteries we use are potentially dangerous — a ticking timebomb if managed incorrectly.

That's why airline authorities always tell you to carry all your lithium batteries in the cabin when you fly. That way if they catch fire the crew can respond quickly. It's why Apple quietly replaced swollen laptop batteries nearly 10 years ago, and why Samsung, despite the massive loss to its bottom line, is currently replacing defective Note7s.

It's also why the UL exists. People like Ken Boyce work very hard to build out the safety science they then disseminate to vendors. If you follow UL's guidelines to a T you're less likely to see your hoverboard destroyed or your vape setting a pocket aflame. Because there exists, within every lithium battery, the potential for thermal runaway. So protect your batteries, keep them out of the heat and make sure you don't overcharge them or use the wrong cable or powerbrick.

And if the company starts a recall on your product return it ASAP. Otherwise it could be your hotel room going up in flames.

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