Once upon a time, in the nuclear submarine navy, my shipmate tags out the ship's battery breaker. As part of the tagout, he checks that the ship's DC bus is deenergized - within the battery breaker box itself. During the check, he finds some voltage, which isn't entirely unexpected, since there is enough capacitance on the DC bus to hold it charged for a while. So he uses a specialized grounding probe - about 1/8" diameter copper rod with a reinforced handle - to discharge it. Unfortunately, he has misunderstood what was inside the breaker box and is actually shorting out the ship's main battery! This is a couple hundred volts DC, and a few thousand amp-hours of capacity, and it delivers enough current to instantly vaporized the grounding rod. He's knocked on his ass by the arc blast. Fortunately, he was correctly considering the box to be energized gear and was wearing a full set of PPE, suffering only minor flash damage to his eyes.
Early on in my 'take things apart for fun' youth, I knew that capacitors held a charge long after power was removed. So when disassembling a camera with built in flash, I popped off the small board holding the 330V capacitor and thought it would be a great idea to discharge it using the end of my needle nose pliers—for the tiny capacitors I'd done this to before, it might've caused a tiny spark, but nothing more.<p>Well, I learned a valuable lesson that day; even relatively harmless camera flash capacitors can pack quite a charge days after a battery's been removed!<p>The giant spark made me jump back and fall over my chair, and my pliers still have two nice molten burn marks where it touched the contacts. I'm just glad the pliers had rubber handles!<p>I'm much more cautious around capacitors these days.
In chemistry class in middle and high school, I thought all the safety precautions we took were stupid, given that we were using harmless chemicals to do harmless experiments. I wish this had been around, and it had been required reading--I would have all about that safety gear.
Darwin award applicant.<p><i>"I had made some gunpowder and had some sitting on an outside table. I was experimenting with fuse design and was burning a fuse 6 feet or so away."</i><p><i>"I bought some H2SO4 and used most of it immediately. Unfortunately the original plastic bottle didn't fit in my cabinet. So I transferred the contents to a couple of small plastic bottles. Finally, the cabinet was temporarily blocked so I decided to temporarily store them on a shelf next to my bed."</i><p><i>"I had a few hundred mL of acetone and H2SO4 waste stored in a glass peanut butter jar."</i>
That 450VDC electrolytic capacitor wasn't the worst failure I've experienced with such a device. I had one let go about 3 meters away from me. It sounded like a shotgun had gone off, and left my ears ringing for a few minutes. There wasn't anything left but the terminals.
In school we had a public display exhibition - a series of LEDs mounted on PCBs with shifters. Like, you put in a color at the first PCB and pressed the "shift" button and the color would shift through the chain, the color of the last PCB in the chain would vanish. Each PCB had a capacitor on the 12V supply rail.<p>So, I needed to swap the PSU because we planned to add more of them, and I plugged it out - and cut the supply cable with a scissor. Twelve capacitors blew out (I believe because the ICs turned off the power of the LEDs before the caps were discharged, they were ridiculously huge anyways)... right in the middle of school day, and a week before there was some retard running amok and killing students.<p>tl; dr: Shorted 12 caps, huge explosion sound, peoples panicked and thought of a school shooting.
> This released profuse magic smoke and severely damaged the power supply.<p>Magic smoke needs a magic fume hood or being outside ;-) I can't say for sure, but I would err guessing a lot of smoke coming out of exploding or burning electronic components is not good for you.