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It doesn't happen often -- statistically speaking, only 1 in 10 million lithium-ion battery cells are likely to go bad. But here's what to do if your device starts smoking. (And keep reading below for why batteries go belly-up.)
Know the warning signs
The battery feels extremely hot or swells up (the device may look like it has a lump or bulge).
That battery (and the device it's in) catches on fire -- admittedly, this one's pretty obvious.
These are important warning signs to know. If lithium-ion batteries -- the kind in nearly all modern rechargeable devices -- do begin to fail, the harmful chemicals they contain could burn your skin if you touch them directly, or endanger your property if you don't correctly douse their flames.
If your device is overly hot, hissing or swelling, do this
Use tools (like a pair of tongs) or gloved hands to touch the device. Leather gloves and polyester clothing are naturally flame-retardant (but not flame-proof). Even an oven mitt or towel is better than using your bare hands.
Immediately turn off the device.
Unplug the device from any AC power source or wall outlet.
Move very slowly and carefully (so you don't jostle the combustive parts together).
Keep the device in an isolated area, away from anything flammable (e.g. on the concrete floor in your garage).
Immediately contact the carrier or retail store where you bought it for further directions.
If the swelling continues to worsen, take precautions to further isolate the device away from people and flammable items (e.g. into a clear area on your patio if you have one, or in an empty metal tool box).
If your device catches fire:
Call emergency services ASAP.
Douse flames with a fire extinguisher.
If an extinguisher isn't available: The US Department of Transportation recommends water spray as an effective suppressant. Depending on the specific components, water should help cool components or dampen flames. However, if the chemical mix is just right (for example, if the lithium in the battery causes the hydrogen to split into a gaseous combustible form), H2O could, in some cases, cause the fire to grow out of control -- especially in a closed space.
Make sure your device is UNPLUGGED from the power outlet before dousing it with water.
Curious what they'd use in a lab? A Class D fire extinguisher, which is specifically made for smothering this type of chemical fire. Class Ds are much more expensive, however, than a typical kitchen extinguisher.
What you shouldn't do:
Do not ignore the problem -- that hissing, swelling or burning smell is a warning sign that requires immediate action.
Do not touch a swelling or ruptured device with your bare hands.
Do not throw the device in the trash; you need to dispose of it responsibly.
Do not breath in fumes, especially if you notice gas or flames (cover your mouth and nose).
Uh, why is my battery hissing or swelling, anyway?
If a battery starts hissing or swelling, your device is already toast, said Bryan McCloskey, a chemical and biochemical engineering professor at UC Berkeley. The various chemicals held at bay inside the battery structure are now running amok. Chemists like McCloskey call this "gassing."
Generally speaking, batteries contain chemicals that need to remain separated to make the battery work safely. In compromised batteries, the chemicals can "slosh around" and cause the battery to short. And if the gases inside ignite, that can lead to an explosion or fire. How big depends on the size of the battery and the makeup of its internal chemicals.
One problem is that different lithium-ion batteries can contain different chemical mixtures and use different methods to keep the volatile ones from touching. So it isn't easy to know exactly which toxins you're dealing with.
Many include fluorine-containing organic compounds, McCloskey said. If volatile hydrocarbons mix with oxygen inside the battery, it can act in ways similar (but not identical to) propane -- the stuff you use to fuel your BBQ.
One last thing
Most retailers and manufactures won't share their guidelines on how to safely transport a device with a suspect battery, so we can't be sure what they'll recommend. However, if it's hissing, it's probably better to seal the device in a sturdy container rather than a plastic freezer bag, and you'll want to avoid shipping it anywhere -- it's hazardous waste at that point, McCloskey said.
Luckily, battery fires are infrequent enough that many of you could go your whole life without encountering a device on the verge of a meltdown. But if you ask us, it's better to know these do's and don'ts just in case.
Editors' note: This story has been updated from its original version with additional details and clarifications. Best Buy, T-Mobile, Verizon and the
wireless association declined to speak to CNET for this story. Samsung, LG, Xiaomi, Huawei, AT&T and Sprint did not respond to our interview requests.