How dangerous are high voltage pulses?

[daqq]

Hi guys,

How dangerous are high voltage pulses? A project I'm supporting has some hardware that creates 10kV, 2us long pulses at a repetition rate of up to 500 pulses per second. The pulses are fairly powerful, can easily provide several Amps of current.

I'm not planning on touching that bit (or getting anywhere near that bit) but I'm wondering, how dangerous are the actual pulses? I honestly have no idea.

What kind of damage would they do to a person who touched the nasty bit?

Thanks,

David

[IanB]

10kV*10A*2us=0.2J. It's gonna ablate a tiny bit of your finger tip, so it's gonna hurt, but it won't kill you.

Also 500 pulses per second, which is 500/s * 0.2 J = 100 W. I think I would say that is quite dangerous, and may very well kill you.

[Electro Detective]

Calling Mr. Smith for this one 

[Mechatrommer]

Calling Mr. Smith for this one 

high voltage tester using acrylic box is totally different from a stuntman job. i will be surprised if there is 2 in 1 person. somebody may call me a stupid stuntman using bare wire but 10kV i have no idea and have no interest at finding out...

[MagicSmoker]

There's good reason to be cautious of any source capable of delivering 10kV pulses at more than a few mA of current, but with a width of just 2us the penetration depth will be very low; perhaps 0.1mm or so. This is unlikely to even make it past the epidermis so won't be felt at all. Then again, it very well might cause RF burns, however, and these are some of the most painful you can experience.

[Stray Electron]

   When I was lot younger I played with a 12,000 volt 100mA Neon sign transformer (a real transformer, not an inverter).  It would knock the S**** out of me but it never injured me.  We could carbonize wood with it and if we let it arc to a piece of concrete for a few seconds it would blow out sections about 1/4" deep and over an inch wide (spalling).  I'm sure it could have caused severe burns but I was only burnt once with it and that was when one of the leads got caught on my hand for perhaps 2 seconds.  Playing with the neon transformer was actually a good learning experience since I went to work on very high powered RADAR a few years later. It used about 20,000 times more power. But thankfully I never got bit by that one.

   The real dander with high voltage isn't the voltage as much as the body's reaction to it.  I will make you jump and/or jerk your arm away uncontrollably and that can lead to falls or striking other objects, or hitting another power source, etc and those are usually a bigger hazard.

   Unlike digital electronics, when you work on high voltage equipment, you need to use an insulated table and stand on an insulated floor mat.   Its also a good practice to keep your left hand in your pocket so that it doesn't accidentally provide a ground path if you touch high voltage.  Current flowing thru the left hand is more dangerous that contacting it with the RH because the LH is closer to your heart so work with your RH and protect the LH.

[joeqsmith]

Calling Mr. Smith for this one 

Not sure what I can contribute.    The KV testing I show is in the ns or 10s of us.  The generator's output is off at the time I touch anything.  There are also two levels of lockout.  Still, if it were to somehow misfire, I limit the energy to 20J for safety.   

The low voltage high energy is more of a concern.  It normally has a shorting bar installed and once it is setup, I stay the fuck away from it.  No big deal really.

If I am uncomfortable with with an experiment,  I will use some cheap gloves.  Normally, I can just setup my test unpowered. 

Not too long ago, when safety came up, I posted several links of idiots who died while working on their microwave ovens.  Some from the transformer but many were killed from the cap discharge with the unit unplugged.     

isnt this somewhat related to the human body ESD test?
like 8kv into 8pf + esr of 12k. which produce some really spikey 15A pulse. very short, but painful?

out of curiosity, I just did a search and right on the front results page is this very interesting NASA test on human electrocution pain thresholds. I had a glance and saw what appears to be tests done on cervical area ... wait what? 

You are correct that the current can easily reach several amps, but ESD is going to be ns, not us. 

[Electro Detective]

FWIW I've had some good zaps and jolts from packing away those common to find white long plastic folding tables, with the tubular metal frame screwed in underneath, after a job end.

The random event zaps were really sharp and disturbing, sometimes taking a few hours for me to feel 'ok' again, maybe a day or two,
far surpassing any mega carpet surfing or car door knob wacks I've had. 

So I got smarter (like there was a choice lol), and used dry leather gloves, but got zapped again just as well, but less likely.
Footwear, rubber or barefoot made no difference.

I was going to ditch the folding tables but would have missed the convenience and light weight

Anyways I finally thought it through properly one boring afternoon waiting for a glued project to cure/dry,
and after some trials and instigated reduced zaps,
figured out to walk around slowly during pack up, and not slide my hands along the table as I was folding it up,
and always start the fold/pack routine with both hands together first (one on top of the other)
and slowly going up and across, and always starting a new move with both hands together again.

i.e. no fixed hand on the table and the other hand sliding about, then raised and grab on etc > or else = 
If I suspect I will get zapped, it's both hands together again, placed on the plastic and metal frame, and start over.

It's easier than it sounds once done (YMMV applies), but for me it's no more zaps, gloves, or mentally buckling up for a jolt required 

I don't know what magnitude of KV and current I was getting from that plastic table zappage, but it felt close to a couple of near demise 240 volt 'can't let go' wacks I had years back (and never again/crossed fingers)
with the same 'hung over' feeling afterwards.

IIRC I copped a zap like this from a wood top table too, maybe from sliding along the laquer, varnish or whatever coating ? 


Hope this helps someone else, especially if the nerves and heart are weaker or getting a bit vintage,
or on-board pacemaker or other support.

Best to be on top and aware, to avoid any such sneaky ESD ordeals no one needs to spoil their day.. 

[T3sl4co1l]

For perspective, ESD is the same magnitude, but about 40 times shorter.

ESD is annoying, and makes you jump.

I wouldn't want to get hit with your pulse.  Whether it's lethal, I don't know, but I don't want to be the one to test it.

I would insulate and handle carefully.

Incidentally, for the same reason ESD is what it is -- a one-contact discharge of your pulse to the body (assuming it has a fast rise time, or if it sparks over) won't feel worse than ESD.  That is, discharging to your body as a capacitor only.  If you're near to anything uncharged or grounded, though (current flows through body), you're going to have a bad time.

Tim

[Berni]

Touching that would most definitely hurt like hell accompanied by a angry 500Hz screaming arc followed by the smell of burnt skin.

I wouldn't really say its entirely safe because of the significant DC component to the signal, but with the short duty cycle i don't think its all that hazardous. Perhaps if you have some sort of heart condition it could be more dangerous, but otherwise you would most likely get hurt because of jumping and falling on the floor or hitting your hand against something hard enough to cause injury as you pull it away. For someone to die from this they would likely need there heart condition tripped by the shock and nobody being close enough to help him with CPR and calling an ambulance.

Just have respect for the high voltage much like you would have respect for high power mains wiring and things should be fine. Always check the device is off before even bringing your hand close, make sure you have clear indicators that show the device has power, if possible have an interlock switch that detects the cover being lifted off the HV parts etc...

[Zero999]

Another thing to consider is whether there's a failure mode which can result in longer pulses? If so then more caution is needed.

[Jwillis]

Its the current that kills. Consider that an average human body has a resistance of 1000 Ohm (damp skin)  to 100,000 Ohms (dry skin)  and it really only takes a small amount of current to injure or kill. Ohms Law.
 

[Berni]

Well at 10kV you don't really even need to consider skin resistance because the high voltage just punches trough it.

The part that makes this 10kV at amps of current a great deal safer is the 2 us pulse length. Its the same reason why shocks from static electricity buildup are not deadly despite involving >10kV and currents exceeding amps effectively passing many kW of power trough that part of your body, but because there is so little charge the pulse is so short that no harm is done by it apart from a bit of swearing.

The internet seams to suggest that static shocks carry about 1 mJ to 4mJ at most 100 mJ of energy: https://physics.stackexchange.com/a/244092

So yeah the pulse from the OP would certainly be quite a jolt, and getting that 500 times per second would certainly not be fun. Id compare it more along time lines of grabbing the spark plug of a running engine. But a tazer is probably not far off as it has a similar repetition rate and energies. These things don't tend to kill people, but as i said someone with a heart condition could be in danger.

[daqq]

Thanks for the info guys. I have no intent of touching the damn thing (or getting anywhere close to it at the moment), I was just curious.

[amyk]

FWIW I've had some good zaps and jolts from packing away those common to find white long plastic folding tables, with the tubular metal frame screwed in underneath, after a job end.

I'd figure out what is getting charged, and find out a way to discharge them. Maybe an ESD strap attached to a good ground, or at least the metal frame... I guess the reason those were so strong is because the tables are big enough to act like capacitors with a relatively high capacitance, maybe even a few nF.

[Electro Detective]

FWIW I've had some good zaps and jolts from packing away those common to find white long plastic folding tables, with the tubular metal frame screwed in underneath, after a job end.

I'd figure out what is getting charged, and find out a way to discharge them. Maybe an ESD strap attached to a good ground, or at least the metal frame...

I guess the reason those were so strong is because the tables are big enough to act like capacitors with a relatively high capacitance, maybe even a few nF.[/size]

I'll roll with your explanation    as it makes sense, especially when my hurried 'slide along' pack up routine was charging up the plastic (or whatever mix it is) 
and coupled with the tubular metal frame somehow,
which zapped me regardless of any/all insulation and or earth ground combos I tried to avoid it. 

I won't be revisiting that scenario any time soon, now that I have the simple ESD avoidance workaround described earlier above,
and can set up and pack away at a decent pace without getting zapped.

Perhaps if I had the right test gear to cope, and a method to capture and document those jolts, I might play Zap Man  one last time for the boys and girls here (= NOT!  )

Funnily enough, I've used those tables to perform many electronic repairs and sensitive test setups with no apparent ESD issues for years 
but still got zapped on the fold/pack up handling