EEVblog Electronics Community Forum
EEVblog => News/Suggestions/Help => Topic started by: kyle on April 19, 2013, 11:44:22 pm
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Hello,
I have searched the channel on youtube and was wondering if there were any videos made on how to be safe with the DC/AC currents. If not could, could we request one? I'm interested in human body properties, how it acts as a capacitor/conductor, what kind of current/hi voltage/hi freq we can pass through our body, e.g. what Tesla did by lighting his bulbs through body during world's fair, how body nerves respond to currents/freq, does strong EMF have any affect on you, how to handle Tesla coils safely? etc... I'm self-taught in electronics, help.
Thanks.
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This is a really basic explanation and don't take it as fact, there are lots of different views on what is "safe"
Anything under 50V should be safe to play with
(It can kill but requires some really bizarre set of circumstances like saturating your skin with salt water)
If you have enough voltage for current to flow through your body then anything under 4mA should be safe (unless you have a weak heart etc..)
3-4mA is around stun-gun level.
Note: If the metal object penetrates your skin then less voltage is required to get the same current.
Therefor a voltage that maybe safe on skin may kill if its pushed through skin into flesh.
DC is far more dangerous than AC.
DC will contract your muscles hard which can stop you from letting go from the thing giving you a shock (no matter how hard you try).
You can get the same "cant let go" effect from AC but its no where near as bad as DC.
The danger of AC depends on the frequency. Low frequencies like <400Hz are quite dangerous for the heart.
As the frequency increases more of the current flows through the outside of the conductor (you) and less through the center.
When you get up to tesla coil frequencies (200,000 Hz+) most of the current travels in the outer 5mm of your body.
Burns are more of a problem with telsa coils due to this concentration of energy on your skin.
Some of the energy does flow through your heart but because tesla coils put out lowish current the danger of death is low. (depending on the size of the coil obviously)
Deep tissue burns from a tesla coil can take months to heal (unlike a soldering iron burn) and tesla coils are still dangerous so never deliberately touch one unless it has been tested/designed to be safe.
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I mentioned muscle contraction.
It's kind of a lose-lose situation ;D
If you use the front of your hand you may not be able to let go.
If you use the back of your hand you may punch yourself in the face. (it happens)
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How about some info on materials handling safety et cetera? Just for fun I hooked 30+ volts up to a 47 ohm 0.25watt resistor the other day, placed it in a glass of chilled non-conducting water, and flipped the switch. I could hear it crackling, see it bubbling and releasing heat. Even though the resistor didn't burn up ang get destroyed, I fear it must have released toxins into the air because I've been feeling sick to my stomached since.
To be fair though, I also did some electrolosys experiments as well and that is probably more likely the cause of air contaminants. Corroding alligator pins and making mixed-metal in electrolyte batteries.
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Thanks for the replies guys :).
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I mentioned muscle contraction.
It's kind of a lose-lose situation ;D
If you use the front of your hand you may not be able to let go.
If you use the back of your hand you may punch yourself in the face. (it happens)
Or you can punch someone else in the face >:D
Years ago I was fault finding some panel, my boss cam round to see how I was going. He was bent over, peering through his bi-focals, behind me whilst I explained what the problem was. I was pointing to things in the panel when I must of touched something and got a bit of a buzz. I yanked my hand back real fast, smacking him in the head. His glasses went flying as he clutched his face and I, with all the strength I could muster to not fall down in a quivering pile of hysterical laughter, trying to comfort him "are you ok?" :-DD