Also in this week's column: Why doesn't a hangover occur the night before? What issues are there for women in space? Why do babies always seem to have a runny nose? Can you die from testing a 9V battery on your tongue? Asked by Liam Johnson of Frankfurt, Germany Here's Liam's question in full: First the simple question: …
you missed the point
You seem to have totally ignored the point that Liam was asking.. He knows that a battery does not have the lethal current levels required directly but was asking if they could effect the nervous system and therefore cause death...
Anyway your response is entirely wrong as you talk about Voltages, everyone knows it is current that kills NOT voltage!
The particular incident with the ohm-meter is recorded in Navy accident records. He actually stuck the leads through his skin. Human skin is actually a pretty good insulator - which is why normally a 9V battery can't kill you. Yes, it's the amps, not the volts, but we all know ohm's law - enough volts and you'll get the amps. But blood is a very good conductor. If you stick the leads through your skin, you'll get a very good circuit - direct through the heart. So yes, that will kill you.
On the tongue won't, because a.) your skin protects you and b.) there's no circuit going through anything particularly sensitive.
The Ohmmeter bit don't work
A normal "ohmmeter" you buy in your local B&Q/HomeDepot/Brico/ <insert favourite DIY chain here> could NEVER do anything that as there is simply not enough power in it to do anything, so i'm afraid to say that that bit about the sailor, as reported, is horseypoo....
However, if you actually meant an "Insulation Resistance Meter/Tester" it could be closer to the truth as the normal ones used in the UK at least (and I guess most of the EU) can fire out up to 1Kv. Yup, that could cause some damage.......
As to the post above, technically he is correct. But since the human body has an average resistance of 2300 ohms, the voltage required to produce a lethal current through the body is obviously relevant, and also it can depend on whether it is an AC or DC power source. The variables are immense. But unless you are talking about people who had heart conditions which could make them "drop" at any time, you generally need in excess of 50v to actually kill someone as that is the lowest possible voltage which "could" allow a strong enough electrical current to "go across" the heart and cause defibrillation (spelling??).
Trust me, I'm an electrician and have had more teaching on the theory of electricity than most people. And I know I have had a hell of a lot more "physical experience" regarding the effect of electricity on the human body...
Oh, by the way, at your normal 230v AC (standard in UK and most of EU unless they use 115v), it only takes 15mA to make every muscle in the body contract, including the heart, (that hurts, if you are lucky to survive. I was lucky, and I was still in pain 3 days later) and prevent you from letting go of whatever you holding. Nine volts, in general, would never do that or worse unless there was already another, underlying, condition already there which would be exacerbated by the electricity flowing. You would also have to be immensely stupid to put yourself in that position in the first case, so I guess you would get what you deserved if it could actually happen.
Hah! Batteries are for wimps.
Many many years ago, when I took delivery of my first Scalectrix set, I had a brainwave of testing the track continuity by touching it with my tongue!
Dont, I repeat, dont try this at home.
From a Neuroscience Point of View
Current is generally what kills but current and voltage are linked together via Ohms law so both can be a factor.
What the article was saying is, if you place a voltage across a nerve cell you can hyperpolarise it (meaning it wont fire at all) or depolarise it (meaning it will fire once then probably die because it can repolarise). This is how if you shocked the nervous system directly you could kill someone.
The current or voltage does not have to be applied across the heart to stop it. If you disrupt the pacer signal from the brain to the heart, the heart wont beat either.
As for the tongue thing, I heard that by placing a 9V battery on your tongue you can cause the nerves to contract around your mouth which can cause you to swallow it.
"Pacer signal from the heart"
There is no "pacer signal" from the brain to the heart. The heart has its own pace making cells in the sino-atrial node in the top of the heart. The heart is, in effect, a self-regenerating electrical circuit. At every heart beat, an electrical wave spreads from the sino-atrial node across the heart, first around the top chambers (the atria) and then, from the bottom up, across the lower chambers (the ventricles). This electrical wave of depolarizing "action potential" (the voltage goes from around -80 / -50 mV to 0 / +15 mV depending on the region of the heart) leads to and coordinates the contraction of muscle cells in the heart.
Electrical currents across the heart can cause the electrical wave to be disrupted, causing chaotic local uncoordinated contractions (fibrillation).
If a further large current is applied, this may, if you are lucky, cause all the heart cells to depolarize at the same time and resynchronize the circuit so that it beats normally again (Defribrillating paddles much beloved of ER).
Coincidentally, this explains why transplanted hearts can beat in a new patient even though they may not be innervated by the vagal nerve. Vagal simulation ("parasympathetic") serves to *slow* down the heart beat, not set the actual rhythm. The heart or cardiac rhythm also responds to a variety of hormones, e.g. adrenaline ("sympathetic" simulation) causes an increase in the pulse.
More lethal than a 9V battery
A close friend of mine, having witnessed my oral 9 volt battery testing technique, decided try it for hinself. However, he chose to test the batter in his electronic flash and, unfortunately, he wrongly identified the flash unit's capacitor as the battery. He was treated to a tongue numbing shock that lierally rendered him speachless for some time thereafter. 'Didn't kill him though <grin>, and I'd be surprisd if a 9V battery would do it either.
Well, as a resident of the Australian (some would say Penal) Colony, I can tell you the reference to 8 people dying in Australia from battery-to-the-tounge-syndrome is rubbish.
Gored by a kangaroo, eaten by a crocodile...perhaps. 9v batteries - nope!
Unless someone has a pacemaker, I believe it not to be possible regardless - except maybe if they had some seriously weird heart condition.
The method of death referred to, involving the nerves revolves around nerves becoming depolarised. When this happens to a significant extent they can not recover.
This is actually the primary method by which criminals are electrocuted (mostly still in the US only) in electric chairs. The secondary method is a lovely cooking of the quite a few of the internal organs beyond the temperature at which they can function (or ever function again).
The present method for electrocution in Florida is as follows:
2,300 volts, 9.5 amps, for 8 seconds; 1,000 volts, 4 amps for 22 seconds; and 2,300 volts, 9.5 amps for 8 seconds. Other states vary. Some like to cook you at 480 volts for 10-15 minutes at the end!
The actual figures vary slightly per "customer" due to differing fat levels etc which effect the resistance. It is typically acknowledged that the first zap does nor depolarise the nerves fully.
Its worth noting that those figures do NOT guarantee success. There are many instances where it has failed to do the job, and thats despite excellent saline conductors to the top of the head and a nice engineered exit path via the ankle.
As you can see it would be pretty hard for a 9v battery to come even close with a "typical" person!
The actual current needed to permanently depolarise nerves is generally agred to be around seventy-five milliamps (75/1000 of an amp), externally applied to the body causes fibrillation of the heart. One amp of current applied externally to the body is sufficient to cause the heart to stop completely.
Whats interesting is that, for example, a duracell 9v battery can peak around 200milliamps - well above the 75milliamps that can end your life. But the natural resistance of the human body is typically between 2,000 and 50,000 ohms, which massively drops the current. Its this same resistance that would likely let you get away with touching the terminals of a car battery while the engine is being started - and 200+ amps are being sucked out of the battery.
The tongue would improve that by reducing the resistance (if you remove the skin, it drops to 500ohms), but not to the extent that you would likely have enough current reaching your vitals to harm you. But in general if you wanted to really reduce the resistance, you would need to apply the shock right in the middle of your chest, quite near your heart.
By the way, a detailed account of the incident with the ohmmeter and 9v battery can be read here: http://www.darwinawards.com/darwin/darwin1999-50.html
I believe it to be an urban myth as even if he stuck them in his thumbs, there would still be considerable resistance between his thumbs and his heart. Now if he dug them deep into his nipples...that I may be able to believe! (Sort of...)
Neither ohm-meters nor 9V are dangerous
I am a US Sailor, that has been an electrician for 19 years. When I was a kid, I used to put 9V batteries on my tongue to check if they were good or not. A 9V battery does not push enough amps to kill you.
As a matter of fact, if you feel the need to put the contact leads of an ohm-meter into your body..... that will not kill you either.
Also, one more food for thought, many of us have played with meggers in our careers. They just give a real big jolt, but then again there is not enough amps to kill you.
A megger is similiar to the old arcade games that you would hold onto the two handles as the game would pass a small amount of voltage through and then slowly increase it till hopefully you will let go.
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