Hacker News new | comments | ask | show | jobs | submit login
Lab explosions and accidents (uvicrec.blogspot.com)
145 points by epsylon on Dec 24, 2015 | hide | past | web | favorite | 32 comments



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.


Lucky guy, lucky too he used a relatively thin rod, a thicker one and it would have been quite a different ending.

I did a similarly stupid thing one day. While repairing a clock for a display on a trade show I hooked the ground crocodile clamp of my scope to what I thought was the ground but which in fact was V- of the DC supply voltage of the neon light installation that was use to drive the display. I had a blind spot in the middle of my eyes for many days after that (and took out a fairly large chunk of the mains supply for the Eastern district of Amsterdam). The crocodile clamp totally disappeared, the scope, miraculously survived and wasn't even out of spec.

Every time I use a crocodile clamp to hook it on to something I think back to that moment when the clamp makes contact and some part of me expects it to happen again.


> I hooked the ground crocodile clamp of my scope to what I thought was the ground but which in fact was V- of the DC supply voltage of the neon light installation that was use to drive the display.

Yeao! I own a couple of high-voltage differential probes for this very purpose. Even though most single-ended scope probes are rated to 300V Cat II, I won't go anywhere near main's power with them.


Pretty hard to top that.

"I bought some fuming nitric acid on eBay and spilled it on the carpet. Dad was pissed."

"I fused two screwdrivers together with a photoflash capacitor. Sears refused to give me a refund."

"I accidentally made chloramine gas and experienced short-term breathing difficulties."

"Yeah, well, I shorted out a nuclear submarine battery."

silence


No, he did not short out the reactor, he shorted out the battery.


Edited just before you posted that comment, because I somehow knew it was coming.

Sigh.


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.

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!

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!

I'm much more cautious around capacitors these days.


Not to brag, but my friend Sean and I are much dumber than you. We took the capacitors out of two disposable cameras and hooked them up inside the casing of a 9v battery – our "9V Taser", we called it. Looked great, but then of course we needed to test it. We decided to do the honorable thing and self-experiment; being the younger and slightly more foolish, I was the subject. We charged it up and he touched it to my arm. I remember my heart sort of "skipped" and I felt really weird for the next couple of hours. Ah, youth.


Similar, but stupider, in my mid 20s while in the Air Force my buddy and I built a rail gun out of disposable camera capacitors. It didn't take long after getting the first capacitor out for us to wonder and discover what it would feel like to short the leads on our skin. That soon turned into a game of tossing a loaded capacitor to the other at various times throughout the day in the hopes that the natural reaction of catching something tossed your way would kick in before the brain figured out what it was catching. Your tax dollars at work.


I did the exact same thing - took apart a camera and noticed the flash capacitor had a shock warning writing right on it, so I thought to myself "I better discharge this before it shocks me." I figured shorting it out using a screwdriver across the terminals would do the trick.

A huge flash arc mini-explosion blasted that screwdriver and left me seeing spots for a few hours.


Smaller electricity lesson. We were studying noise on resistor-capacitor circuits at uni (waveform), with an oscilloscope. Teacher says to the most "experimental" student of the class: "You know, even 220V has noise at the top of the curve". The second the teacher turns his back the student put the probes in the power point.


What happened? Did the scope have over-voltage protection or was it fried?


The oscilloscope actually survived, as a surprise to me. The power went out at the building, level, classroom and desk level, but no actual damage.


It should have survived, depending on the probe in use and the input circuitry of the scope. But most quality scopes would just display a sine wave after you scaled down the Y axis a bit. Mine certainly would (elderly Tek).


Wow. How does that work? I mean, stuff like diodes etc. all have maximum voltage levels, not to mention PCB trace clearance or the rated voltage of coil isolations. And a scope can measure stuff in the mV range, so any op-amps or other electronics should be fried in a second when hit with a 1000-fold increase in voltage.


There's a classic book called "art and science of analog circuit design" and there's a whole chapter on scope inputs.

The TLDR is at the input you limit lightning / hand of god level of voltages using the usual RF techniques for lightning protection, so you never have to protect against more than a couple hundred volts, then implement a ridiculously high impedance / voltage attenuator such that it'll arc over before the output exceeds a volt or so, then you limit the output with (optimistically) low capacitance diodes to the power supply. Then a buffer that converts from high impedance in to low output impedance and from there on its pretty boring analog stuff, gain stages etc.

Or the TLDR of the TLDR is you have multiple protection stages and (controllably) attenuate the heck out of the input signal. Also you rely on some ohms law tricks... a voltage big enough to damage in series with a ridiculous resistance will be a very low current which any protection diodes can survive.

Its a tricky business to work around all the RC time constants that occasionally are not fun at all.

Three things to think about. Everyone uses 10x 100x 1000x scope probes, so when you sniff 460V VFD power you're probably using a 100x probe and only measuring 5 volts or so. Also protection circuits tend to protect against the usual 60hz and DC overvoltages... shoving the output of a MRI amplifier at hundreds of MHz will just arc across and blow it to bits. Finally its possible to build RF front ends that sniff RF down to thermal noise limits, and scopes throw all that away to survive hundred volt transients on the input; I assure you ultra low noise microwave preamps will not survive more than a couple volts input, but those are bazzilionths of a picowatt not mV range.

Oh and a warning... you pick up a 100x scope probe, your scope handles up to 500 V input (perhaps) so you think you're good to 50000 volts in, but the probe has its own input voltage limit and unless you have bottomless pockets it probably tops out around 2.5 KV, so if you try to measure a 35 KV flyback transformer for an old fashioned CRT using that 2.5 KV probe, kaboom...


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.


    Takeaways:
    Don't store strong chemicals in your bedroom
Some of these seem the wrong side of irresponsible


Darwin award applicant.

"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 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 had a few hundred mL of acetone and H2SO4 waste stored in a glass peanut butter jar."


Yeah, I enjoy occasional shenanigans with dangerous items and substances as much as the next nerd, but this guy is just plain reckless. He needs to find something else to do, preferably before something tragic occurs.

He's incredibly bright (the X-ray machine with the 2D positioner is just plain brilliant) but he just doesn't seem to think far enough ahead.


Some of these incidents seem to have occurred when he was a child


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.


Reminds me of a similar situation. We were working on a device powered by what looked like a 6 pack of 16 Oz cans caps charged to 500V. SCRs controlled the discharge of the capacitors into the device and caps were charged in opposite polarity so that the device could deliver current in opposite polarity depending on which way the mechanism was to move. There was a flaw in the logic that controlled the SCRs and in some circumstances both directions were on resulting in a direct short between the two banks of caps, discharging all stored energy in a fraction of a second (about 300 ms IIRC) That resulted in catastrophic failure of the SCR which propelled pieces of casing across the room and left my ears ringing.

I asked that a cardboard box blast shield be placed over the H/W before participating in further tests.


Fantastic! I love reading accident reports, for some reason. There's so much practical knowledge contained in them.


> Think twice before "stop, drop, and roll" as the floor may be on fire

Wow. Just... wow.


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.

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.

tl; dr: Shorted 12 caps, huge explosion sound, peoples panicked and thought of a school shooting.


I'm almost glad I didn't pay more attention in chemistry class because I'm sure I'd do some of these blunders.


> This released profuse magic smoke and severely damaged the power supply.

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.


How is this dude not dead yet?!


This dude is really passionate. I don't know anyone who did chemistry for fun, let alone had any budget and enough parent leniency to do it before 18yo. As he grows up you notice he talks more and more about security gear.

I don't know how someone can get into chemistry before 18. I understand reactions that are presented to me, but how do you get the initiative of trying something new? How can I be confident those are the only reactions that happen? OP has only produced H2S by mistake a few times in his life, far fewer than I'd expect anyone experimenting to produce unexpected chemicals.


> I understand reactions that are presented to me, but how do you get the initiative of trying something new?

This is what kids do naturally, before they know any better. A lot of kids experiment with chemistry. The trick is keeping them alive and unmangled until they develop a respect for what they're working with.


In my attempt not to drill my young kids' exploration out of them, I tell them that "X is a tool, not a toy!", for values of X like knives, fire, light sockets, etc. And then promptly talk about how to use them :)




Applications are open for YC Summer 2019

Guidelines | FAQ | Support | API | Security | Lists | Bookmarklet | Legal | Apply to YC | Contact

Search: