"Back to the Future Part II" got it partly right. As of 2015, the hoverboard is a real form of transportation that lets trendy kids get into trouble while effortlessly zipping along the sidewalk. There are a handful of important differences, though. These self-balancing scooters don't actually hover like the ones in the movie.
Also, they could potentially catch on fire and burn your house down.
The US airline industry has decided not to take any chances: American, Alaska, Delta, Hawaiian, JetBlue, Southwest and United Airlines have banned hoverboards on passenger flights, and the US Postal Service has stopped shipping hoverboards by air as well. Amazon and Target both temporarily suspended sales, and Overstock.com has stopped selling hoverboards at all.
What the heck is going on? Keep reading.
Hoverboards have become one of the hottest news stories this holiday season, and not just because they're selling like mad. According to the US Consumer Product Safety Commission, there have been 12 incidents in the United States where the lithium ion batteries in these hoverboards reportedly caught fire as of December 2015, destroying bedrooms and even entire homes. In July 2016, the CPSC updated that number to at least 60 reports of hoverboard fires totaling over $2 million in property damage.
The fires have started in all sorts of different circumstances, too. According to owners and witnesses, some of the hoverboards exploded while charging, others while riding and one while it was simply sitting near a kiosk in a Washington shopping mall. (There have been several other hoverboard fires reported in the UK, and at least one in Hong Kong.)
Here's the really scary part: there's no single reason why these hoverboards are exploding, and there's no sure-fire way to avoid potential catastrophe if you want to buy one yourself. There's no particular brand of hoverboard to avoid -- they all seem to come from thousands of interchangeable factories in China -- or any label on the box that guarantees a product won't explode. And much of the advice we've seen issued by local fire departments and government agencies isn't likely to help.
For instance, officials have been warning that you should only use the charger that comes in the box. That sounds like common sense -- until you realize that these hoverboards tend to use a plug you won't find on any other type of device. Since you're so restricted when it comes to which type of charger you can use, it's pretty unlikely that any of these fires occurred due to someone mistaking a laptop charger for a hoverboard one.
Similarly, many officials now warn against overcharging hoverboards, but when was the last time you had to think about overcharging a gadget? With modern laptops and smartphones, you simply plug them in and leave them there, trusting that they'll automatically shut off the flow of electricity when they're done.
While the US Consumer Product Safety Commission was on the case as of December 2015 to figure out the actual root causes of these incidents, they didn't have the answers when we first published this story. "We want to be able to deliver for the public, but we hope they'll be able to appreciate that what's going on right now is a very thorough science-based investigation," said CPSC spokesman Scott Wolfson in late 2015.
But in February 2016, the organization officially warned that hoverboards pose a serious risk, and threatened to block imports or recall hoverboards that don't meet voluntary safety standards.
And in July 2016, the CPSC followed through on that threat, recalling half a million hoverboards in the United States. The cause: overheating lithium-ion batteries.
The science behind hoverboard fires is actually pretty simple, and fairly well understood. Much like your laptop, tablet or phone, these hoverboards use lithium ion battery packs for their power, and it just so happens that the liquid swimming around inside most lithium ion batteries is highly flammable. If the battery short-circuits -- say, by puncturing the incredibly thin sheet of plastic separating the positive and negative sides of the battery -- the liquid electrolyte can heat up so quickly that the battery explodes.
You don't necessarily need to stab a lithium ion battery to set it on fire. A defective battery might have tiny sharp metal particles inside that could puncture the separator all on its own. "When this happens, especially when the batteries are charged, a lot of heat is generated inside the cells and this leads to electrolyte boiling, the rupture of the cell casing, and then a significant fire," Carnegie Mellon University materials science professor Jay Whitacre told Wired. You can see what a lithium ion battery fire looks like in our Droid Turbo 2 torture test video:
It shouldn't be a revelation that lithium ion batteries are volatile, because fires like these aren't exactly new. We've been living with potentially deadly explosions in our pockets and laptop bags for years. In 2004, a spike in the number of cell phone battery explosions prompted this CNET report, and Dell recalled millions of laptop batteries in 2006 after just six incidents of fire. More recently, Boeing had to ground the 787 Dreamliner airplane until it could find a way to keep its lithium ion batteries from overheating.
Safety standards, or the lack thereof
If lithium ion batteries are so volatile, why are we still using them today? The traditional argument is that the energy density of lithium ion batteries is significantly higher than batteries that use less flammable materials. (In other words, a lithium ion battery can be smaller, lighter, and/or last longer than say, a lithium iron phosphate one.)
Another reason is the consumer electronics industry has gotten much better about safety standards, to the point where most of us don't think twice about leaving a phone connected to a charger. "We said to the companies, you need to come together, create a voluntary organization and set a safety standard," says the CPSC's Wolfson, recalling how we went from big battery scares and recalls in the mid-2000s to the relatively safe laptops and phones we have today.
Most modern batteries now incorporate all kinds of safety measures, such as emergency vents, and many products filled with lithium ion batteries have to endure a barrage of drop tests, crush tests and electrical stress tests before they can pass.
But hoverboards are brand-new. "It's a product without a safety standard," says Wolfson.
Sean Kane, a longtime product safety researcher, says cases like the hoverboard are precisely why his nonprofit organization The Safety Institute is advocating for more general categories of safety standards like "computers" and "personal mobility devices" instead of the specific ones that exist today.
There are existing standards for motorized scooters and toys, says Kane, but the hoverboard just doesn't fit. "What you have is a product coming in here where no one knows which safety standards are applicable."
For now, retailers like Amazon and Target are making sure individual components of these hoverboards -- namely the batteries and the chargers -- have been certified for safety. (As of December 2015, Amazon asked that all hoverboard sellers provide proof they comply with UN 38.3, UL 1642 and UL 60950-1, specifically.)
But before you breathe a sigh of relief, you should probably know that while batteries and chargers can be certified individually, it doesn't mean those hoverboards have been certified as a whole. Until those parts have actually been tested together, it's more of a legal cover-your-ass measure for the manufacturers and retailers than anything else.
And you might not be able to find a hoverboard that's been tested in its entirety by a reputable independent firm like Underwriters Laboratories (UL) even if you looked hard. Swagway, one of the more popular brands, claims its entire hoverboard is UL-certified because it has a UL-certified battery and a UL-certified charger inside, but that's not accurate. "There are presently no UL-certified hoverboards," says UL consumer safety director John Drengenberg. (Incidentally, Swagway is now facing a lawsuit from when one of its hoverboards caught fire.)
Besides, there's another problem with certifying batteries instead of the hoverboards themselves. There's no easy way to tell what kind of battery is inside a hoverboard -- or if it's a counterfeit.
Update, March 2016: Underwriters Laboratories now has a testing procedure for hoverboards, UL 2272, and we got an early look at how it works. Also, some self-balancing scooter companies now claim to follow that standard. See the UL's testing procedure in the video below.
Supply and demand
When an increased number of cell phone batteries were bursting in 2004, many blamed cheap counterfeits made in China -- batteries produced with far less stringent standards than phone manufacturers might have wanted.
That's a popular theory when it comes to the hoverboard fires, too. "There are some factories right now that will say they use Samsung batteries, but don't," a sales manager for Chinese hoverboard manufacturer CHIC told Quartz. "They wrap a piece of paper around the battery that says 'Samsung' when it's not Samsung."
But unlike cell phones, it's not like we have known reputable hoverboard manufacturers that merely got a bad batch of batteries to go with their own carefully designed proprietary components. Even the top hoverboard brands -- Phunkeeduck, IO Hawk, Swagway -- are ones you've probably never heard of, ones that sprang up out of nowhere to take advantage of the hoverboard craze.
And those companies are merely distributors for a sprawling array of factories in China that supply components to one another practically interchangeably.
That's not a reflection on the quality of Chinese manufacturing in general, by the way. Practically every high-quality Apple product comes off a Chinese assembly line, not to mention those of Lenovo, a Chinese company that's one of the top worldwide computer vendors. But China has also become famous as a place where tiny factories can pile onto a hot new idea like the selfie stick or the miniature R/C helicopter, churning out copycats in record time.
By the time the hoverboard fad took off in the United States, there were already too many Chinese companies building hoverboards to tell who came up with the idea first. Practically every hoverboard you see is a counterfeit, in that sense.
"Right now there are thousands of workshops making identical hoverboards in China, and the only obvious differentiator is the costs," says Jay Sung, CEO of popular electric-scooter company EcoReco. And since there are so many different ways these Chinese companies could have cut costs among the different components they trade with one another and piece together to form the final product you see, it's hard to narrow down the actual point of failure.
So far, some reports have blamed the batteries, others the cables, but we don't know for sure. The UK divisions of retailers Amazon and Costco are specifically telling customers to destroy charging cables that have plugs that weren't built to UK safety standards. (Costco is providing replacement cables, while Amazon is offering full refunds.)
Another possible culprit is the cut-off switch, a safety feature that keeps an electronic device from overcharging, which the UK's National Trading Standards consumer protection agency says can often fail in these hoverboards. EcoReco's Sung suggested that to save costs, some hoverboard manufacturers might not even include a cut-off switch to begin with. That's clearly not the issue everywhere, though, as Mashable recently tore down a Swagway hoverboard that appeared to have a cut-off switch installed.
What happens now
In the UK, the government is already cracking down on hoverboards. Not only is it illegal to ride one on public roads or walkways, but the UK National Trading Standards body has now seized and reportedly destroyed 32,000 hoverboards in December 2015 -- the vast majority of the 38,800 devices that the organization has been tracking since it started investigating the devices in October of that year.
In the United States, the Consumer Product Safety Commission has now recalled half a million hoverboards, and is pushing for voluntary standards like the ones that made laptops and phones safer today.
It could also be that the CPSC pushes to ban hoverboards altogether. It wouldn't be the first time a popular product was deemed too unsafe to sell. There are good reasons that lawn darts and magnetic Buckyballs, both popular toys, were banned. (Fires aren't the only reason that hoverboards are dangerous. The CPSC has received "dozens" of reports of injuries from falls from US hospital emergency rooms as of December 2015.)
Perhaps next time, we could reserve the name "hoverboard" for a gadget that actually floats above the ground.
Original story published December 22, 2015
Update, January 21 at 2:27 p.m. PT: The US Consumer Product Safety Commission is now investigating at least 40 reports of hoverboard fires across 19 US states.
Update, February 20 at 1:15 p.m. PT: The CPSC has officially warned that hoverboards that don't meet voluntary safety standards pose "an unreasonable risk of fire," and has threatened to recall or ban imports if manufacturers don't follow those standards.
Update, June 8 at 4:02 p.m. PT: The first hoverboards meeting UL's new safety standard are now on sale in the United States.
Update, July 9 at 3:43 p.m. PT: The CPSC has officially recalled half a million hoverboards due to lithium-ion batteries that were found prone to overheating.