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January 22, 2007 8:25 PM

idiotgeekfilter: Should I be worried about a 330v shock?

So... I got shocked by the 330v flash capacitor in my digital camera. Yes, I know. (Really, I know.) But it happened anyway.

Symptoms: I got a sharp pain at the entry point (my thumb), then Guantanamo-style muscle pain running up my arm and stopping in my bicep. Also, I yelled. Loudly. Then I dropped the camera and felt like a big, fat, moron.

Upon collecting myself, I called my Health Care Provider, and they ran me through the usual questions: I answered "no" to the most serious ones (loss of consciousness, etc.), but I do have some lingering arm stiffness and pain (like I got a flu shot), noticeable dehydration, and general freaked-out-ness that could also be classsified as shortness of breath. There's no visible wound on the thumb.

My question, oh amateur doctors of the internets: Do I have anything to worry about? The consensus is that shocks below 500v are not too serious -- but also that it all depends. There's plenty of info on the web about how dangerous shocks from 330v camera flash units can be, but no examples of people who've been shocked and lived to tell about it. My main concern is that I'll wake up dead tomorrow from some sort of hidden damage to my ticker organs, or that my arm will necrotize and drop off at a socially embarassing moment.

Why don't I go get checked out at the hospital? Having gone to the extremely unpleasant Urgent Care exactly once in my life, I have no desire to return unless I'm sure I'm on death's door. (The place is a breeding ground for SARS.) I feel fine, mostly. But electricity is a mysterious force that scares me, and I fervently hope will one day be harnessed for the good of all mankind.

posted by turducken to health & fitness (28 comments total)

it's happened to me before (same thing - fucking around with my camera and accidentally got across the flash cap - ouch). i was fine.

if you don't have any immediate symptoms i wouldn't worry too much. less relevant than the voltage is the amount of energy deposited in your body; in the case of a (relatively) small capacitor like you'd find in a camera flash, that's not very much.
posted by sergeant sandwich at 8:35 PM on January 22, 2007

If the capacitor was labeled 330v, that is the limit of the part, not what it was necessarily charged with. You're fine.
posted by fatllama at 8:36 PM on January 22, 2007

It's the amperage, not the voltage that'll kill you. You're fine.
posted by now i'm piste at 8:41 PM on January 22, 2007

now i'm piste is right. Those warning signs that say "high voltage" are probably a little imprecise.... they should really say "high amperage," because that's what kills you, but the general public seems to understand "voltage" more than "amperage". However, If your symptoms don't go away in about a week or so, you may want to get checked out.
posted by fvox13 at 8:50 PM on January 22, 2007

You're walking? You're talking? You're not in pain? You're fine.
posted by ASM at 8:52 PM on January 22, 2007

You're fine. That capacitor charge is more than enough to be dangerous if applied strategically (eg don't hold the camera circuitry in both hands, for example, in case one terminal connects to one hand, and the other through your other hand. Even then, you'll probably survive, but your heart will slam into your chest like you've never felt before. Or it could be Very Serious... a roll of the dice) but getting a shock on one hand is generally pretty safe.

Which makes for a handy tip - when working around high voltage, you can increase your safety by putting one hand in your pocket.

If it makes you feel any better, many of us have been there - there are lots of nifty projects people make out of camera flash circuits, and nearly everyone making such things gets a belt or two off the cap at some point. You're not alone :)
posted by -harlequin- at 9:04 PM on January 22, 2007 [1 favorite]

It's not necessarily high amperage that will kill you, low amperage can kill you just as bad. High voltage (say 120 volt household current) allows the current to pass through the resistance of your skin. 100-200 milliamps if it passes through your heart is enough to put your heart into fibrillation and kill you. That's why you always need to treat electricity with respect.
posted by Eekacat at 9:06 PM on January 22, 2007

If you're still alive to read this, you'll be fine.

But don't be stupid next time.

Easier said than done, I know from experience.
posted by dirigibleman at 9:20 PM on January 22, 2007

I remember looking this up when I got shocked arm to arm by my wimshurst generator. If I remember correctly so long as you didn't lose consciousness, your heart didn't go in to fibrillation and your heart rate isn't dropping beats you're fine, but I don't think any of us are doctors so you still might want to ask one. (covering own ass)
posted by subtle_squid at 10:03 PM on January 22, 2007

This happened to me all the time as a kid. I had gotten ahold of a couple dozen old flash units from disposable cameras and, after discovering the jolt they produced through sheer accident, proceeded to wrap them in electrical tape and hand them out to friends at school. Hilarity ensued for a short time as random individuals were zapped for a few days. Then someone got caught and, of course, mentioned the creator of the little toys and that ended my miniature reign of terror. No one was injured (but boy, were they pissed).
(No, I don't advocate running around zapping people with this, it can kill someone with a heart condition.)

That said, this is most dangerous when you touch the negative and positive electrodes with different hands, as this allows the current to flow directly through your chest.
posted by IronLizard at 10:04 PM on January 22, 2007

Just to give you an idea of the energy involved, a typical camera capacitor is rated 180 uF and 330 V. The energy stored is given by the formula E = 1/2 * V^2 * C where E is the energy in joules, V is the voltage and C is the capacitance in farads.

For the camera capacitor this works out to about 10 joules. For reliability, the camera would never be charged to its full rated voltage, so the actual energy would be somewhat less than 10 joules.

Compare that the energy in a hospital defibrillator which is somewhere between 120 and 400 joules, applied directly to your chest.

So the shock you got is much less than one-tenth of what you would get from a defibrillator. You may be feeling funny from the adrenaline rush and some temporary soreness from the violent muscular contraction. Don't worry about it.
posted by JackFlash at 10:08 PM on January 22, 2007

I managed to catch 240V, more or less straight from the wall, when screwing around with a Sega Saturn. Didn't do anything to me that I'm aware off.

On the flip side, a faulty Dyson vacuum cleaner gave my mom a mild shock and she had severe cramps in her legs for a month or so that only stopped after she'd been taking a particular dietary suppliment for a while (Calcium+Magnesium I think).
posted by krisjohn at 10:09 PM on January 22, 2007

There is such a thing as delayed arrhythmia as a result of electric shock, but I gather that it's not common.

It's hard to give a simple rule of thumb for what kind of shock can screw up your heart. It only takes a very small amount of current to do it, but getting that current to go through your heart (which is surrounded by alternative conductive pathways, and wrapped in your relatively nonconductve skin) usually requires a lot more voltage (and current) applied to the outside of your body.

The other possible kind of injury that wouldn't be totally obvious would be hidden burns, as you mention: it's possible to have a channel of burned, dead flesh inside your body, going between relatively small entry and exit wounds in your skin. And this is bad. But I'm pretty sure it takes a lot more than a camera flash capacitor to cause that kind of injury. (More linky.)

I am not a doctor, but I do play amateur science geek at home and have shocked myself countless times, and I think you're probably fine. With something like a camera flash, the most likely kind of injury is as a result of muscle contractions --- you can throw yourself across the room, into a wall, onto a sharp object, etc., when your muscles spasm.
posted by hattifattener at 10:18 PM on January 22, 2007

I shocked myself pretty badly while disassembling a busted digital camera a couple of months ago -- definitely bridged the contacts of one of those supercaps with my thumb. It stung like a -----, but did no long-term damage that I've detected. I've also been shocked several times by 120v, once or twice across two hands, and thusfar lived to tell about it.

It isn't that I reccomend doing it, it's just that so far I'm not dead. :p
posted by Alterscape at 10:59 PM on January 22, 2007

10J is more than enough to give you heart problems... IF it went via your heart. If the shock was just across a thumb or arm (most likely), then you will have no issues whatsoever. However, your description of the shock travelling your arm is worrisome since it means it may have travelled through your thorax.

10J is not enough to burn anything but the contact point where you got bitten, think 4.2J/g.K specific heat of water; you need about 60C for a burn which means that the current must have heated (100% efficiently, with no thermal leakage or heat dissipation in the capacitor!) at most 0.1g of you for any burning to take place.

You're not going to keel over. Probably. But if you look at any OH&S policy, the rule is that anyone who has a shock goes to see the doc, no matter how fine they feel. The reason is that your heart can be doing strange and mildly dangerous things and you can't know unless someone competent inspects your ECG or you die of it. The latter is unlikely but definitely within the realm of possibility.

What matters for heart-stopping is the current passing through your heart and (I believe... IANAD but IAAEE) the shape of the trailing edge of the current spike. 15-30mA depending on age & health of the victim is all that is required to cause fibrillation.

A full flash capacitor will discharge its approx 0.1C in a few milliseconds, resulting in currents in the many-amperes range which is very very bad if it goes the wrong place. Don't assume the capacitor was under-charged, many of these go to 20% over the rated voltage: I know this because I harvested a few hundred from disposable cameras for use in a coilgun.

Next time keep one hand in your nasty little pocketses.
posted by polyglot at 11:10 PM on January 22, 2007

A friend and I used to do this for fun (back when we were idiots, natch, we're much more refined now). As far as I know I still get brain good.
posted by !Jim at 1:25 AM on January 23, 2007 [1 favorite]

Moreover, you'll never get rheumatism now :)
posted by Phanx at 3:03 AM on January 23, 2007

as they've said above, its not the volts but the current that kills. not enough current produced by camera batteries to kill a human being, generally speaking. tho you might die of embarrasment. ;)
posted by jak68 at 3:11 AM on January 23, 2007

As a kid, I once got a speaker transformer off the back of the speaker from an old valve radio, hooked the amplifier-side terminals up to an improvised Jacob's Ladder made of paper clip wires stuck in a block of polystyrene foam, then hooked the speaker-side terminals up to a variable-voltage AC lab supply and slowly wound up the variac. The separation at the bottom of the Jacob's Ladder was about 6mm, and I ended up with quite a nice fat spark jumping that gap, so I'm guessing I was generating about 6000V peak.

The arc climbed the ladder a few times, then just stopped; the wires had got hot, and one of them had melted the polystyrene foam a little and sagged. Without even thinking about it I reached out with both hands to adjust the spacing between the wires...

BLAM!

I had been doing all this while lying face down on my bedroom floor with my feet sticking out the door into the hallway. I still have a distinct memory of being mad at my sister for a few seconds afterward, because I was absolutely convinced she'd sneaked up behind me and jumped on my back; it was only when I noticed that there was actually still nobody else in the room that I realized that I had very nearly just killed myself.

My whole torso felt bruised for about three days.

AFAIK my heart's still fine (I didn't get it checked, because that would have involved fessing up to Mum).
posted by flabdablet at 3:51 AM on January 23, 2007 [5 favorites]

It's the amperage, not the voltage that'll kill you. You're fine.

It's not the amperage or the voltage, it's the total power. Don't mess with 1000V at 1A, or the reverse, unless you know what you are doing. 1KV @ 1KA is right out.

High voltage, here, is relative. Compared to the 5V or less that digital circuitry runs, it is very high. Compared to 440V three phase, it's meh. NEC defines high voltage as anything over 600V.

Note that in digital circuits, a "high" voltage may merely represent a 1, which could be as low as 1V, depending on the gates.

The real line -- if it'll spark across open air, you need to be thinking HV. Depending on factors, the lower limit for that is about 350V.
posted by eriko at 5:51 AM on January 23, 2007

Dunno man, but when I was a kid I used to play around with the electrician, and I've gotten shocked by high voltages and currents lots of times. And not from capacitors, but from running generators. Hurt a bit, but that was all.

You'll survive.
posted by markesh at 5:58 AM on January 23, 2007

You just built one of these.

I'm in the middle of doing something else similar, but different, basically connecting ~3-4 of these caps in series to build a nasty little rat trap for the critters who have taken up residence in my home.

AFAIK Most disposable camera caps are 330V @ 100uF, the caps I bought on ebay are a little meaner, 400V @ 10uF, so I have no worries they'll do the job.
posted by TomMelee at 6:09 AM on January 23, 2007

Lots of people are relaying stories of electrical misadventure summing up with "I was fine, you'll be fine". You should keep in mind that the people struck dead by household current aren't posting to metafilter.

turducken you'll probably be fine but electricity can be tricky. If you're at all worried you should see a doctor, especially if the pain lasts more than a week or you experience any weakness. I know of someone killed by a (much larger) capacitor discharge across a hand and I've experienced a significant burn from a capacitor (which I admit I didn't seek medical attention for).

I know you know but for the archives a suitably sized resistor on a stick can be used to discharge capacitors safely.
posted by Mitheral at 7:13 AM on January 23, 2007

Very likely you're fine, but I think there is some possibility that such shocks can kill or damage sensory or motor neurons, eiither by direct heating effects or by depolarizing them below the limits the cell's metabolism can recover from. I remember hundreds of phone numbers back into childhood, but when I get a shock strong enough to make my arm jump away, most of those numbers are completely gone until the next day.
posted by jamjam at 9:07 AM on January 23, 2007

a nasty little rat trap for the critters who have taken up residence in my home.

I started doing that and one of the units is floating in my junk box somewhere. Then I moved and forgot the whole thing :)
posted by IronLizard at 9:19 AM on January 23, 2007

One thing to keep in mind is that most common capacitors people deal with today hold a relatively small charge capacity compared to a fairly new technology:

http://en.wikipedia.org/wiki/Ultracapacitor

These tiny beasts are typically rated in full farads and in some cases even kF -- not nF, pF or µF. An ultracapacitor the size of a normal flash camera capacitor can hold 120F at 2.5v (750 joules), compared to the standard camera capacitor holding 100µF at 330v (9 joules).

Fortunately 2.5v is pretty low, but they do come in larger voltages too.

If you're like me and love to take stuff apart, it's good to know about these for future reference. Be careful! =)
posted by joquarky at 2:39 PM on January 23, 2007

I love you all. Thanks for the reassurance, and the very familiar tales of electrical adventurism! (As for me, I started at 7, shoving a copper cotter pin into a household outlet, with a pair of popsicle sticks as insulating tongs.)
posted by turducken at 7:48 PM on January 23, 2007

And specifically? Those "200" "300" "360" calls you hear the docs on $MEDICAL_SHOW calling out to the defibrillator nurse? Those are in joules.
posted by baylink at 8:54 PM on January 23, 2007