Here’s Why Samsung Galaxy Note 7 Catches Fire.

After 35 reported incidents of overheating smartphones worldwide, Samsung made the unprecedented decision to recall every single one of the Galaxy Note 7 smartphones sold.

That’s said to be 1 million of the 2.5 million that were manufactured. (Since the recall was first announced, the number of explosive Note 7’s has nearly quadrupled.)

The company stopped all sales and shipments of the Note 7, worked with government agencies and cellular carriers around the world to provide refunds and exchanges for the phone, and apparently it still wasn’t enough: as of October 10, 2016, as many as five of the supposedly safe replacement Note 7 phones caught fire as well, and

Samsung asked all users to shut down their phones. On October 13, Samsung officially recalled every single Note 7, including replacement units.

The science behind phone battery fires is actually pretty simple, and fairly well understood.

Much like the infamous exploding hoverboards, phones 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 puncture point becomes the path of least resistance for electricity to flow.

It heats up the (flammable!) liquid electrolyte at that spot. And if the liquid heats up quickly enough, the battery can explode.

The FAA is strongly warning passengers not to use or charge a Note 7 on a plane, and many airlines are explicitly banning their use.

Why Note 7?

What makes the Note 7 different: Samsung may have accidentally squeezed its batteries harder than it should.

According to a unpublished preliminary report sent to Korea’s Agency for Technology and Standards (obtained by Bloomberg), Samsung had a manufacturing error that “placed pressure on plates contained within battery cells,” which “brought negative and positive poles into contact.”

“The defect was revealed when several contributing factors happened simultaneously, which included sub-optimized assembly process that created variations of tension and exposed electrodes due to insufficient insulation tape,”

Why didn’t the phones catch fire immediately?

When Sadoway explains these theories, one thing doesn’t seem to add up. Today’s cell phone batteries generally charge faster (and get hotter) when they’re first plugged into the wall, not at the end when they’re trickle-charging the last few percent to reach their maximum capacity.

But these Note 7 phones didn’t explode right away. In practically every reported instance of a Note 7 catching fire or exploding, it happened after the phone was plugged in and left charging, sometimes overnight.

Then, there’s the little matter of how Samsung plans to make these phones safer — by issuing a firmware update that keeps the Galaxy Note 7 from charging to more than 60 percent of its full capacity.

How could that possibly help, if things heat up the moment a phone is plugged into the wall?

Sadoway has a theory — albeit one without proof. What if only part of the battery was squished improperly, so that the phone couldn’t tell when it was 100 percent charged, and kept on charging the cell?