There's nothing funny about Samsung Galaxy Note7 phones inexplicably exploding and torching cars and burning people. And it's definitely not a joking matter when their replacements, which are supposed to come with safe batteries, are catching on fire (like on a plane) as well.

Whatever the real reason is — a design flaw, defective batteries from a specific supplier, a process mistake — the Note7 is unsafe to own. Samsung's permanent halting of Note7 production is basically the final nail in the coffin.

SEE ALSO: The Samsung Galaxy Note7 is done

Samsung is still trying to find the exact cause, or causes, of these battery fires. While that investigation continues, it's worth asking to what extent overall trends in smartphone design contributed to the debacle. Every year the devices in our pockets get new features, bigger batteries and improved — often thinner — form factors.

Image: brittany herbert/mashable

As anyone who has played Asphalt 8 knows, phones get hot when pushed to their limits. Regardless of which company and phone you're a fan of, it's important to understand that any device — not just phones — with a lithium-ion battery could explode under certain circumstances.

Of course, that almost never happens, even with Samsung products. So was the Note7 fiasco a unique fluke of poor quality assurance? Or have the demands that we've put on today's smartphones — thin, powerful, waterproof and more — been pushed so far that some kind of crisis was inevitable?

High demands

Image: raymond wong/mashable

Designing smartphones is hard. As consumers, we're not versed in the challenges of building a phone to the precision, performance and features that today's premium phones pack.

It's not our job to understand that stuff. That's for the engineers and designers to figure; we put our safety in their hands.

If you just look at today's phones, it's not hard to see how they've evolved. Where phones used to be thick slabs made of plastic with small batteries, most cutting-edge phones are now metal, super thin, have huge, energy-dense batteries (many of which are capable of quick charging) and are water-resistant.

It's incredible that engineers have figured out how to squeeze all of these features into ever-thinning bodies.

It's incredible that engineers have figured out how to squeeze all of these features into ever-thinning bodies.

These tightly packed, svelte designs leave little room for proper heat dissipation from the increasingly demanding tasks (3D games, live streaming, multitasking, 4K video recording, etc.) we use them for.

Meanwhile, water resistance, though extremely convenient for consumers, also potentially complicates matters. Water-resistant phones are rated with different Ingress Protection ratings (IP), which determine how deep and for how long they can be submerged; they're more sensitive to pressure than phones that aren't water-resistant.

Mix the excessive heat generated by the higher-density batteries with the added pressure sensitivity and you've got a dangerous environment — at least, more dangerous than a few years ago — should the phone combust. That's why it's more important than ever to guard against that happening.

Image: brittany herbert/mashable

Lithium-ion batteries such as the ones in your phone combust because of something called thermal runaway. Basically, it's a temperature chain reaction. Once the temperature of one part of the battery gets too hot, it releases the stored energy suddenly, causing another part to get hot, and another, and another, and before you know it the gadget bursts into flames.

Phones contain a slew of sensors and software that monitor and regulate temperature. When a phone begins overheating, it'll usually throttle down the processor to allow it to cool down. A battery manager also stops phones from overcharging after they've reached 100 percent.

Mashable reached out to Scott Croyle, Chief Product and Design Officer at Nextbit Systems, the company behind the Nextbit Robin Android phone, to get his insight on whether exploding phones were inevitable given their tighter tolerances and increased feature set. Prior to Nextbit, Croyle worked at HTC between 2002 and 2008 and led design for many of the company's iconic phones including the One series.

"I don't see it as inevitable," Croyle said. "[Designing smartphones today] is no tougher than designing a feature phone 15 years ago. You're always kinda pushing the edge [in terms of stress tests]."

There are various testing stages (EVT, DVT and PVT) that phones must meet before they can be mass manufactured he explained.

"There's all these safeguards," Croyle said. You come out with an initial layout, you do a thermal analysis, then you test them in the real world, and you have a best case and a worst case scenario. There should be nothing in a phone to cause it ever to explode."

More energy in smaller package

Croyle's statements would be reassuring, except the Galaxy Note7 did just that. The Note7 contains the highest capacity battery out of any Note — a feature Samsung proudly boasted.

Image: raymond wong/mashable

As you can see in the chart above, the Note7's battery capacity has mostly increased over the years while the physical space for the rest of the phone's components has shrunken.

Compared to last year's Note 5, Samsung somehow squeezed in a battery with an extra 500 milliamp-hours (mAh) without dramatically growing the phone's dimensions to accommodate it.

The problem with physically cramming more energy into a phone that's already extremely starved for space is that it makes the environment within the casing that much more volatile when something goes wrong — the magnitude of damage is amplified. As outlined in the chart below, the Note7 has the most energy-dense battery and it's packed into an even smaller volume — more than any Note before.

Image: raymond wong/mashable

According to Bloomberg, a U.S. consumer-safety agency said the original recalled Note7's which had batteries reportedly produced by Samsung SDI were "slightly too large for the phone" and the replacement phones, which contained batteries produced by Amperex Technology Limited (ATL) also might have had an issue, but it's unclear if those batteries were also slightly too thick.

Another report from the New York Times, citing documents leaked to Korea's SBS (via PhoneArena), suggests the Note7's fatal flaw might have been caused by defective Samsung SDI batteries that contained isolation plates that were packed too close towards the device's curved edges. Applying additional pressure on the compacted battery cells could have triggered thermal runway:

The plates inside the SDI battery were too close to each other near its rounded corners, making it vulnerable to a short circuit, according to the documents, and the battery also had defects in its insulating tape and the coating of its negative electrode.

Andrew Goldberg, an iFixit teardown engineer told Mashable he didn't want to jump to conclusions. He said he didn't see anything weird that jumped out when he examined teardowns of the Note7 and the S7 Edge. Their casings are both similarly dense with circuitry and so, too, are the air gaps surrounding the batteries that allow them to safely swell up when overheated.

"I don't think you're looking at a complete failure of the design", Goldberg said. "If one of them has the susceptibility [to explode due to a higher energy battery], the other one does as well.

Galaxy Note 5 The Note 5 has a 3,000 mAh battery. Image: ifixit Galaxy Note7 The Note7, which is roughly the same dimensions as the Note 5, has a larger 3,500 mAh battery. Image: ifixit

Goldberg is right the Note7 and S7 Edge are very similar, but the Note7 has even less internal space to fit the large battery since a good chunk is occupied by the S Pen stylus. The S7 Edge's display is also smaller, which means it likely sucks up less power, too.

"For the Note7, [Samsung] could have just pushed their demands a little higher on the [tolerable pass/fail test curve during production] and now your outliers are going to be a little too big," Goldberg says. "Our running theory is a manufacturing tolerance [defect]. I don't think that every Note7 is at risk of exploding at all."

In comparison, Apple, takes a more cautious approach. Rather than dramatically increasing the battery capacities in its new iPhones, Apple optimizes its processors and iOS to achieve greater power efficiency.

While nowhere conclusive either, iFixit teardowns for the Plus-sized iPhones suggest there is more breathing room for the batteries compared with Samsung's Notes. The downside, of course, is that the Plus-sized iPhones have larger dimensions. In hindsight, any sane person would take a larger phone that's safe over one that's smaller and prone to catching fire.

Explosions unlikely, but risk isn't worth it

A notification warns users it's too hot to operate. Image: therese mcpherson/mashable

In September, Mashable conducted an experiment on three new Galaxy Note7 phones that were on the recall list.

Instead of returning them and exchanging them for "safe" replacements, we decided to see just what it would take to make them combust from overheating.

The goal was to see if Note7's were fundamentally flawed and prone to combusting completely out of the blue from charging.

We kept all three Note7's plugged into power for four continuous days in a fireproof building at the Morris County Fire Training Academy in New Jersey and livestreamed the entire thing.

The result was surprising and not so surprising: None of the Note7's exploded.

As expected from a high-end device from a brand-name electronics company with years and years of experience building phones, the Note7 was built to meet certain acceptable heat limits.

When the phones reached about 136.4 degrees Fahrenheit, a notification popped up saying it was too hot and was powering down.

This is a safety precaution that all modern phones display to prevent people from ignoring the intense temperatures and pushing their phones to the point where they could explode.

Three Note7's out of up to 2.5 million recalled devices globally is in no way definitive, but it does lend merit that under normal everyday circumstances, the phones are unlikely to explode.

It wasn't until we placed a 1,000-watt heat lamp directly over one of the Note7s (RIP "Leftie") and overheated it to 152 degrees Fahrenheit that it finally burst into flames.

That the Note7s didn't explode suggests the battery controllers were working properly to regulate power and prevent overcharging and, thus, overheating.

More evidence needed

The consensus from many of the experts Mashable spoke with was unsurprisingly similar: More evidence is needed to better understand what went wrong and ultimately doomed the Note7.

Though it's believed Samsung may have rushed the Note7 to beat the iPhone 7, Croyle said "[Phone makers] are always rushing to production; they're never not rushing."

It's truly unfortunate the Note7 turned into such a nightmare for Samsung. More thorough investigations will no doubt reveal in greater detail what caused phones to explode — perhaps it was the culmination of many factors and defects during the manufacturing process.

Dong-jin Koh, Samsung's mobile president, told South Korean reporters last month a "flaw in the manufacturing process resulted in the negative electrodes and the positive electrodes coming together" and said the defect was difficult to identify.

Samsung's no newbie when it comes to building state-of-the-art phones that give consumers features they want. With the Note7, though, it's very possible that existing technologies and design tolerances just couldn't keep up with Samsung's dream design. Simply put, the components — probably more than one — just weren't ready to come together yet.

The phone had it all — high-performance specs, a huge screen and a huge battery jammed into a body that's smaller than other phablets — and now it's no more.