Safety concerns regarding high voltage

[TheAmmoniacal]

So, I've acquired this spark gap igniter (https://www.sparkfun.com/products/11218) for a small project of mine. The project details is not important, what I'd like to know is some more details on this device. Most relevant is the voltage output I can expect from a 1.27 cm (0.5") spark? (current?) I always try to minimize any risks associated with my projects, but assuming a mistake was made and I were to be zapped/jolted by it, what could I expect? What if I were to touch both cables as it was powered up? What sort of gloves would be recommended to avoid that happening? And the brightness/UV from the sparking, would regular darkened sunglasses be a good filter? Or would you recommend a welder's mask?

And if anybody happened to know more about how these exactly work, I would also be interested to hear from you. Transformer? High voltage inverter? Capacitor? Both?

[poorchava]

I'd say a flyback transformer-based inverter. Based on some stuff I know about tesla coils, the output voltage might be >10kV for .5" discharges. As effects on yourself, I'd guess similar to a taser.

4,8V @ 3A is about 15W, so rather low current on HV side. I don't know for sure if it's enough to cause fibrillation, but my guess would that it can't (given that you don't have a pacemaker or some stuff like that)

[amyk]

The dielectric strength of air is approximately 3kV/mm, so a 1.27cm speak means ~38kV.

[Maxlor]

I don't know for sure if it's enough to cause fibrillation, but my guess would that it can't (given that you don't have a pacemaker or some stuff like that)

A couple of things I know about causing fibrillation:

• You can cause fibrillation even in a healthy heart by jolting it at the right time, i.e. in between the S and T points (in an EKG, there's this huge 3-pointed spike, the 3 points are labelled Q, R, S. During the next 100ms or so, there's a curve, the end of which is labelled T.)
• Don't worry about it too much though, because a healthy heart will recover from fibrillation within seconds.
• If your heart starts fibrillating and doesn't stop, you'll lose consciousness after 5-10 seconds. You have about 2 minutes for someone to rescue you (by doing CPR and eventually stopping the fibrillation) before brain damage sets in.
• Even healthy people get atrial fibrilliation if they're intoxicated enough. As you might guess, atrial fibrillation is mostly harmless though, it just decreases the heart's efficiency in the short run. If it happens very frequently, you might see heart damage (but your liver might be the bigger issue at this point.)
• Even if you have a pacemaker, it should weather a high voltage accident just fine. Those things are robust. Just don't fall on a magnet that might trigger its reed switch and make it shut off.
• On the other hand, if you have an ICD, it might think something's seriously wrong and it might shock you. Which is rather painful if it it happens because the ICD is confused by outside signals. (If it happens because you really need it, you won't feel the pain since you'll be unconscious.)
• External defibrillators usually operate in the 1.5kV range. But, they stay on for more than just an instant, I think they're on for up to 100ms per pulse, and they might inverse the polarity several times, depending on the manufacturer's particular algorithm. Very short pulses don't do anything to the heart... although that information applies to that same 1.5kV range. I don't know about the minimum time to effect something for the 40kV range.

So if you're experimenting with sparkgaps, I'm thinking that you should limit it to single shots until you can enclose your experiment. Even if everything goes wrong and you get the full jolt, you'll survive it assuming you're healthy. If you have it trigger every 0.1s and you can't get free, that's trouble.

[IanB]

I always try to minimize any risks associated with my projects, but assuming a mistake was made and I were to be zapped/jolted by it, what could I expect?

You could, at a minimum, expect it to be really, really painful. A high voltage jolt will cause a muscle spasm which feels like being whacked with a large object, which may leave your muscles feeling sore for some time afterwards. A related danger is that you may jump violently and injure yourself by banging your head or other body parts on nearby objects.

If the shock happens to go through your chest then you could risk death through disturbance of your heart rhythm, but if you keep one hand behind your back the risk of this will be minimized.

Do not rely on gloves to protect yourself. The kind of glove that would insulate against a multi-kV potential would be too thick and heavy for any detailed work.

Just follow normal safety precautions: unplug and switch off before touching anything, and discharge any capacitors first.

[Paul Moir]

With that much energy the light output will be very low.  The UV component isn't a concern.

FWIW, the ~2mm thick polycarbonate dirt shield on my welding mask does almost all the UV-C filtering, the LCD is just to dim out the visible light.  Note most safety glasses and eyeglasses are made these days of polycarbonate.  Blocking UV-C is not hard.  Transmitting it is though; you're mostly looking at quartz, water or air.