In midair.

Via Starbase1.co.uk
Which is sort of like asking Fred Flintstone to take over for your 18-wheeler's engine while it barrels down the interstate.

So, 20 seconds into its flight, the whole rocket stalled. Which was very, very bad, because that rocket booster was full of rocket fuel as it plunged back down to Earth. The resulting explosion was huge, yet the Soviets somehow managed to keep the whole disaster a secret until the fall of communism. And that was when we got a hold of this footage:

Yep. We're thinking this should be in every single workplace training video in the world. This:

The largest explosion in the history of rocketry ...

... was the result of one freaking loose bolt. One. Yet that blast was minor compared to what's coming.

... turned a city into freaking this:

Via Semp.us
-holy what the hell!

It started with the sort of project that you wouldn't think could lead to an explosion no matter how badly you screwed it up. In the 1980s, a contract worker was tasked with a pretty straightforward job -- lay down some water lines so the good people of Guadalajara, Mexico, could enjoy continued access to city water.

It was an easy job, too, because space had already been dug for a separate set of lines (for gasoline), so it was as simple as laying his water lines in the same trench. There's no way that can start an apocalyptic wave of destruction across the entire city, right?

Surely if it could, the Joker would have thought of it already.

The Disaster:

Fast forward a few years. On April 19, 1992, residents of the city noticed that their water smelled like gas. Local officials heard one complaint after another about smelly toilets and drains, and then someone noticed gas vapors coming out of the manholes.

Within two days, those vapors morphed into full-on smoke columns. And since the Guadalajarans weren't living in the "Thriller" video, this was a pretty alarming development. What if Ninja Turtles were real and they were in danger underground? Or worse, what if Ninja Turtles weren't real, and something else was going on?

Photos.com
"No, all I see is darkness and shit. Does that mean I'm a goth?"

Well, that gassy smell in the water? Turns out that was gas. Highly combustible natural gas. The city's water was so explosive that something as small as a lit cigarette or a particularly hard finger snap could ignite it. And remember, these pipes were running under the town, so it's like everybody was suddenly living on top of a gigantic landmine. And before anyone could figure out how the gas got there or what to do about it, the first explosion hit.

Via H2Oreuse
It was the one time in history that "my toilet smells like shit" actually meant something important.

We say "the first" because 10 more followed.

Each blast erupted under the busy streets of the downtown district. And we're not talking about little pops, either. One actually sent a bus flying. In fact, some of the blasts registered as high as 7.1 on the Richter scale recorded in Mexico City, hundreds of miles away. When all was said and done, 6 miles of sewer lines were destroyed and the city looked like post-blitzkrieg London.

Via H2Oreuse
We've never seen a semi truck writhing in agony before.

Eventually, investigators discovered that the whole shebang came back to that anonymous contractor who placed the city's water pipe over the state-owned gas company's pipe. It turns out that the water pipes were made of zinc-coated iron, and the gas pipes were made of steel. Put them together and you get a reaction that leads to corrosion. After a few years of water dripping down onto the gas pipe, holes formed, gas started to leak and somebody learned a horrific lesson in not cutting goddamned corners.

The company in this case was PEPCON, whose job was producing a particular compound that was pretty much used exclusively as space shuttle fuel. But by 1988, the space shuttle program had been frozen for over two years, thanks to the Challenger disaster. The product this company was producing was temporarily obsolete, like Jason Bateman between the years 1991 and 2003. By all rights PEPCON should have stopped and just made guest appearances on The Love Boat and Hollywood Squares for a while.

Via W. Oelen
"Well, OK, but don't let it sit next to Charles Nelson Reilly. You're just asking for trouble."

The Disaster:

Instead, for two years PEPCON kept making this fuel that no one needed. Piles and piles of the stuff. And then, because no one was buying it, they ran out of places to put it. They were like the hoarders of the chemical company world, but instead of dead cats and used diapers piled to the ceiling, they had 4,000 tons of amazingly combustible rocket fuel, which they eventually stored in plastic bins.

Now, we're not rocket scientists, but if we were, we'd probably know that these particular plastic bins were oil-based, and that this particular rocket fuel compound was an oxidizer. And that one welding spark could set off a pretty big explosion. Here's video of what that looked like:

On May 4, 1988, their stockpile of fuel went off in an explosion that was the equivalent of 2.7 kilotons of TNT. It left a crater 200 feet wide and 15 feet deep. It killed two people and caused $100 million worth of damage.

So, you know, the lesson here is you should store your rocket fuel in good, sturdy containers. Did you really need us to tell you that?

Photos.com
Maybe something like this -- though we admit, we don't know anything about rocket fuel.

The actual disaster was a little more complicated, but not by much. When the SS Imo finally got refueled, the harbor was logjammed with typical wartime traffic -- and the Imo wasn't piloted by the most patient of captains. On one side of the narrow channel conveniently called "The Narrows" was the Imo, which picked up speed to pass dawdling ships. In the oncoming "lane" was the Mont-Blanc, a ship loaded with explosives on its way to France. And even though the Mont-Blanc had the right of way, there was nowhere for the Imo to go -- the space was too narrow. As a last ditch attempt to avoid the collision, the Mont-Blanc made a hard left and the Imo reversed its engines. If only one ship had made a move, things might have worked out alright. Unfortunately, it didn't.

Between the TNT, the picric acid, the guncotton and the straight-up oil on board, the Mont-Blanc didn't stand a chance. Neither did anyone else in the harbor or surrounding city. The Halifax explosion would go down as the largest unintentional man-made explosion ever -- and that record still holds.

Via Wikipedia
The explosion was felt and heard up to 220 miles away.

The Disaster:

Apparently, there was. On November 3, 2004, two employees at the N.P. Johnsens Fyrverkerifabrik fireworks factory in Denmark dropped a box. In that box were fireworks. And somehow, some way, the simple friction that resulted from the drop ignited the fireworks in the box and a fire started. A fire in a fireworks factory.

Abovetopsecret.com
Which isn't so much pretty as it is goddamn apocalyptic.

Every explosive in that factory erupted, one after another, in the most spectacularly horrific spectacle that you can possibly imagine. Yes, people were injured, one person died, homes were destroyed and the whole thing was a terrible, awful tragedy. But holy shit, wait until you see the video of what the explosion looked like:

As far as spectacular accidents go, you're not going to top that. Not unless it was, like, a nuclear bomb or something ...

That's kind of what happened in 1954, when the guys in charge of testing the hydrogen nuclear bomb slapped together their bomb juice and they had to make a call -- which kind of lithium to use? We could go into the technicalities of what different types of lithium do to a dry fuel thermonuclear hydrogen bomb, but really, unless you're a supervillain, those details aren't important. What is important is that one type was thought to be inert (and thus would just act as filler) and it wasn't. So it was kind of like if they accidentally made a whole cannon out of gunpowder.

Via Wikipedia
About half a second in, everything looks good so f- OH, HOLY SHIT!

But, it's just a hydrogen-bomb test. What could possibly go wrong?

The Disaster:

So they're ready to test their bomb at the Bikini Atoll, in the Marshall Islands. The scientists are at a safe distance to observe an explosion that they figured would be in the neighborhood of 4 to 6 megatons (equivalent to 4 to 6 million tons of TNT).

So they lit the fuse and realized how totally wrong their math was.

Via Wikipedia
"Do you think anyone saw?"

They watched as a fireball 50,000 feet tall erupted in front of them, and kept growing. The explosion formed into a mushroom cloud 130,000 feet tall -- almost 25 miles straight up, the height of 90 freaking Empire State Buildings stacked on top of one another.

The stem part of the mushroom cloud was over 4 miles wide, which looked tiny compared to the 62-mile width of the cap.

When it was all done, the eggheads calculated that the final yield was actually 15 megatons; two and a half times more than the expected 6. Within an hour, radiation levels at the forward observation posts were high enough that the scientists in charge had to evacuate to an emergency bunker.

The islanders who actually lived in the area didn't have that bunker-hiding luxury. They eventually returned to the islands, only to find out decades later that the radioactive soil was poisoning everything they grew.

Photos.com
"Oh, no, this is all perfectly fine. Well, goodbye forever!"

There was one tiny bright spot out of the whole screw-up. A Japanese fishing boat was exposed to the fallout as well (that's not the bright spot, by the way) and outrage over America's recklessness inspired someone in Japan to spin the whole horror story into a real horror story: a little one called Godzilla.

For more large impressions from tiny sources, check out 5 Tiny Mistakes That Led To Huge Catastrophes and 7 Bullshit Rumors That Caused Real World Catastrophes.