If someone tries to make a cool new device, make some chemical concoction, magical or alchemical spell, etc., and such an attempt fails (or is sabotaged by a rival or prankster), then the failure will result in a comical explosion, with a cloud of smoke, and ash on someone's face.
This tends to happen even if the device/concoction doesn't have any agents that can cause an explosion. Basically anything involved in these will be Made of Explodium somehow.
Science is not inherently dangerous when properly prepared, but many scientists in fiction fail to wear things like safety goggles or crash helmets. Luckily, this trope is typically Played for Laughs, so Ash Face is the worst of their worries, whereas death or dismemberment could be a potential consequence in real life experiments. Explosions aren't harmless, despite what a certain trope would lead us to believe.
A Sister Trope to Disastrous Demonstration (and is often a result of those demonstrations), Readings Blew Up the Scale, Explosive Instrumentation (both are devices blowing up for other reasons), Explosive Overclocking. Often used to Trash the Set.
- Tenchi Universe opening has Washu causing an explosion in her lab.
- Played for Drama in Baccano!, messing around with a chemistry set ends up getting Nice a lost eye and a lot of burn scars for her trouble.
- Subverted in the very first scene in Futari wa Pretty Cure, which introduced Nagisa and Honoka. Though Honoka's experiment does result in an explosion, the results are just as she had predicted.
- In What's Up, Doc?, Judy recalls how she accidentally blew up a school chemistry lab. She tells Howard that though she was part of the student protest movements, she was just taking a class there.
- Willy Wonka & the Chocolate Factory: Charley Bucket's science teacher has him help mix nitric acid, glycerine and a special mixture of his own to create a wart remover. Do you know what you get when you mix nitric acid and glycerine together? You get nitroglycerine. The mixture explodes but only creates a lot of smoke. With the amount they mixed together, in Real Life it could have leveled the entire building.
- In Young Tom Edison, after mixing a bunch of chemicals, Tom accidentally re-invents nitroglycerin and has to get it off a moving train before it explodes.
- The beginning of the original The Nutty Professor (1963), the one with Jerry Lewis, may qualify. Prof. Kelp blows up his lab and gets chewed out.
- At the end of Flubber, Robin Williams's character is getting married via video screen as he continues his experiments. He mixes two smoking chemicals together assuring his bride that "there is no chance, that anything could go wroooonnnngggg!!" as his house explodes. Again.
- About halfway through the Malloreon, Garion, Belgarath, and Beldin are visiting the College of Alchemy in Mallorea. Explosions are so common the building was reinforced to handle them.
- Discworld. The alchemist's guild in Ankh Morpork blows up with such regularity, people aren't even alarmed anymore.
- In Falling Free, lampshaded with the smoke test of the one-off replacement vortex mirror on the super-jumper.
His quaddies moved fast. Within minutes the vortex mirror was fitted into its insulated clamps, its alignment checked. "All right, gang. Let's move back and let Ti run the smoke test."
"Smoke test?" Ti's voice came over the com. "What's that? I thought you wanted a ten-percent power-up."
"It's an ancient and honorable term for the final step in any engineering project," Leo explained. "Turn it on, see if it smokes."
- Discussed for laughs in The Moonstone, where Rachel's guardian Mrs Merridew is convinced that any scientific experiment will inevitably end in an explosion. Becomes a Brick Joke when Rachel needs to get her out of the way in a hurry, and achieves this by telling her the explosion's imminent.
- Safehold: The (re)discovery of guncotton in Charis follows the same pattern as the Terran discovery noted under Real Life — Doctor Lywys uses a cotton lab apron to clean up after an acid spill, holds the apron in front of a lamp to dry, and the nitric acid and sulfuric acid take it from there.
- The Big Bang Theory, episode 22 of the third season "The Staircase Implementation", a series of flashbacks to sometime before the series began, shows Leonard explains to Penny the story of why the elevator in their building has been out of order since before she moved in. As it turns out, Leonard was testing an experimental rocket fuel in a giant model rocket that he was going to launch with his buddies. Sheldon realizes the chemistry is unstable and quickly moves the smoldering rocket into the elevator where it promptly explodes moments after the door closes. This lead to a change of heart for Leonard who felt indebted to Sheldon for saving his life.
- Invoked trope in the Stargate SG-1 episode "Bounty", where Dr Lee is giving a "demonstration" of a new device to the wider scientific community not in on The Masquerade and has rigged it to short out, smoke and spark, to make believe it is a highly temperamental prototype and not something they stole wholesale from Aliens.
- This is part of game mechanic in Deadlands, especially in the simplified Savage Worlds edition (the first edition had way more fun and destructive ways for inventions to malfunction).
- Warhammer 40K: Any ork teknology, since to them a good explosion and the ensuing destruction is just as desirable an outcome as the intended use. Their heavy use of Tim Taylor Technology doesn't hurt either.
- Champions supplement The Blood and Dr. McQuark. Dr. McQuark is an absent minded scientist/inventor. The first time the PCs visit his laboratory, there's a minor explosion caused by one of McQuark's experiments/inventions.
- Dungeons & Dragons 1st Edition. Module L1 The Secret of Bone Hill. The PCs can find a number of potions that had been experimentally mixed together. Under the standard rules, mixing potions together could cause an explosion.
- In Genius: The Transgression this is the safest thing a wonder can do when it malfunctions (which can happen if it's damaged or if a mere mortal gets too close and starts pointing out that it shouldn't work).
- Forgot in Magic: The Gathering in the Ravnica expansion the Izzet Guild has a huge amount of explosions.
- Gadgeteer Genius Li Kohran of Sakura Taisen often makes devices that blow up instead of working.
- In Anno 2070, anytime your laboratories are building something, there's a set chance of them spontaneously blowing up, setting the whole building on fire and (sometimes) spreading disease throughout the nearby area. This is true even when they're working on things you generally wouldn't expect to be particularly combustible, like a water-filter - or maybe some firefighting gear...
- Pajama Sam: No Need To Hide When It's Dark Outside had a mad scientist's laboratory room with a bench containing color chemicals. A recipe book displayed all the spell combinations, but if a three-color permutation that wasn't in the book would be mixed, the result was harmless Ash Face, which Sam would wipe off with his cape and remark that he should have read the instructions.
- League of Legends: The Blast Zone skin for Heimerdinger, a Magitek Einstein, has had some contraption blow up in his face. Complete with Ash Face.
- The basic plot element at the beginning. A failed experiment causes the test chamber to explode, in what is termed a "resonance cascade".
- Later in the game, a scientist and security guard are overheard discussing a new type of gun the scientist developed, called the Tau Cannon. The scientist warns the guard that the gun has a possibility of overloading, when suddenly there's an explosion, killing both and blowing out a wall.
- Professor Layton and the Unwound Future: The time machine explodes both times it is powered on. Lives are affected. The case in the present was intentional, making this an invoked trope.
- In the opening of Teenage Mutant Ninja Turtles (1987), Dontello's elaborate device turns out to accidentally be a rocket launcher.
- Jonny Quest TOS episode "The Invisible Monster": Dr. Isaiah Norman is conducting experiments with energy and mass. The process gets away from him and a large explosion occurs. Dr. Norman finds out too late that the explosion is the least of his worries.
- The Simpsons
Down in the basement, Homer works out a few equations on the chalkboard, hammers, saws, welds, and finally blows up the basement. Walking over to a chart, he changes a "greater than" sign to a "less than" sign, and goes back to work. Later, a much bigger explosion rocks the house; walking over to the chalkboard, he erases a stick of dynamite from his schematics.
- When Homer decided to become an inventor, there's a big explosion. Description from snpp.com:
- Another Simpsons example occurs in the episode where Bart is mistaken for a child genius, in which he blows up the school during a chemistry lesson.
- There's an episode where Homer manages to make cereal catch on fire, just by pouring milk, does that count?
- In the second act of the Mr. Bogus episode "Babysitting Bogus", Bogus is dressed up as a chemistry professor on TV where he is preparing to pour one chemical into another beaker. When he does so, however, this causes an explosion that destroys the interior of the laboratory.
- An episode of Phineas and Ferb has the title characters working on rockets. Each time they try and fail, a major explosion, accompanied with stock footage from the 1950s, wipes out the backyard and most of their clothes. Each time, they go back to their chalkboard and modify their equations.
- Happens pretty often in Dexter's Laboratory.
- 'The Loud House: Lisa's experiments have a high risk of exploding, especially if they involve chemicals.
- Alfred Nobel is a serious example - before he got the formula for dynamite right, his brother died in a lab explosion.
- Building bombs and other devices intended to explode. The failure here being the bomb detonating while in its stages of development.
- A practical way of making guncotton (the first smokeless propellant/explosive found) was discovered when Christian Friedrich Schönbein spilled nitric acid and sulfuric acid in the kitchen. He dried it up with his wife's apron, and left it to dry near the fire. Shortly, he had a violent and spontaneous combustion.