When I was a kid, I was building a Tesla coil. One of the early lessons with the car ignition coil on the primary side was that high voltage pulses can jump almost a half inch.
Similar lesson, occasionally relearned, is that a metal screwdriver is conductive.
Another Tesla coil lesson was quite noisy. I had a car battery charger as its power supply, homemade one my dad designed, and with no capacitor on the output; the pulsing voltage is better for the charging. So I added a cap. The first day it worked well. The next day when I rebuilt the rig it was rather underperforming; the power was low, it was not what it used to be even at the highest output setting (custom-wound transformer with taps from 8 to 18 volts, I think). Then suddenly,
and all I saw was grey. Before the shock that I don’t see sunk in, a green light of the main power (the charger) poke through, then the red light of the aux PSU (a model train transformer) made itself visible. I switched them off, and only then the startle reaction came in and the electrolyte started burning in my eyes.
The fog disappeared shortly, enough to see the workbench being all covered with something that looked like spilled grey guts; that was the guts of the capacitor. Its casing was on the other end of the room.
In the haste to get it running, I connected the cap the wrong way. For a while it sunk power like a lousy diode, generating heat and gas, while I fed it more and more energy in attempts to bruteforce the original performance.
When I was making a stepper motor driver, I used four H-bridges with those little epoxy-capped transistors. Controlled from a parallel port, each base to one pin. And it all worked well - until I touched something wrong and reset the computer. All the D0…D7 went H, all the transistors opened, and I never found the caps from most of them.
A minor explosion of a pill bottle with electrolysis rig when hydrogen decided to have fun. Startling but inconsequential.
Some minor chemical and solvent spills. Some smoke. Some overheating electronics that burned and stank; nothing that would even remotely compare with my mom forgetting a pot of milk on the stove, that stench lingered for DAYS.
Gulping a 0.1M HCl when pipetting when distracted. No lasting harm but my pride dissolved.
Testing a neon lamp with a resistor, for a keychain for mains sensing. I have an adapter, with lightbulbs to limit current that can be connected in series with the load; one of the handiest toys I designed. I had the bulb-resistor assembly in series on the top output clamp that was supposed to be L, the bottom being N. It was not shining when I touched the free end. It was shining when touching the N pin. I touched the ground pin and touched the free end, to lower the resistance (DUMB!, what was I thinking!), nothing. After a while of messing, I touched the N pin, and
and I got one. A horse kicks less, I’d reckon. After I recovered a bit and the rest of my hair settled back on my head, I did a post-mortem analysis; the whole mishap hinged on the assumption that the L and N pins are where they are (the N one was live, and vice versa). Major oops. Tracing to the sockets, it turned out that while the first power strip is wired correctly, with L in the left hole, the next one (you run out of sockets rather quickly here) was not. I used a piece of a computer power supply cord, remain from a project where I need a cable with one wall socket and several IEC sockets, and trusted the wire colors; that was a mistake, Chinaman swapped the blue and the brown so in the second power strip the right was L and the left was N.
I upgraded the lightbulb limiter, added a L/N swapping switch to the back, and a pair of neon bulbs to the pins on the front (against the safety ground) to indicate which one is live. Always strive to indicate where the voltage is.
Welding a long weld, I did not button up my shirt. Got a rather intense first, almost-second degree V-shaped sunburn on my chest. In the middle of winter. (Twice.)
Welding a shorter weld, I laid a nice “caterpillar”, and knocked off the hot slag, which broke off in a nice big piece and landed on my shirt sleeve. And was getting warm through the thick flannel. No worries, I brushed it off gracefully. It landed in my glove. I still have the scar.
Making a movie prop (a display for a timebomb) from a smart display (expensive 4-digit part) and a microcontroller that needed 12 volts for programming. Iterating through the software, switching the power supply between 5 and 12 volts. Once I did not switch it back; killed a $50 part and wiped my profit from the project. The $4 microcontroller (I think it was PIC16C84) survived.
Repairing a display in my boss’s laptop. One of the wires to the lid was chewed and the image was getting distorted. (One of the LVDS lanes.) I repaired it, all goes well, at the final test I pushed the board and disconnected something when I was not supposed to; the whole thing died and couldn’t get switched on anymore. Luckily it was scheduled for upgrade anyway, so we did data migration from the old one and the upgrade was done a couple weeks ahead of schedule. The wounded pride still hurts several years later.
I may remember more.