Hi to all,
I have never seen a discussion about whether or not you can get electrocuted by the ni-cad or lith-ion batteries. Now that these batteries are up to 36 V at keast, should workers beware especially if we are standing in a puddle. I know that tools are double insulated, but still wondering if there is any danger.
Thanks, Larry Haun
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Replies
You can stand in the water upto your neck.
The batteries are isolated power, ie one side is not grounded.
To have any affect you have to be "connected" between the two terminals on the battery.
And since those are fairly close together you won't have much affect.
But even with one hand on one terminal and the other on the other hand at 36 volts it will still have minimal affect.
And with DC it won't affect the hear. That is one of the problems with AC.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I'm just going by my memory of when I was in school but I think in ideal conditions you would need a minimum of 40 volts to push enough current through your body to kill you. This would be -- you're hot and sweaty, making good contact with each hand to the two terminals of the battery so that the current travels through your heart. Like the previous post said, grounding yourself in a puddle won't do it unless the battery is also connected to ground.
I'd be more concerned with a fire from a spare battery getting shorted out by a loose nail in a tool box.
To be injured by electricity, you need to have certain conditions:
1. The voltage has to exceed the contact resistance of the skin (generally in the 12V to 24 volt range, varies depending on moisture, etc.)
2. A circuit path. That means you would have to be in contact with either both battery terminals or something conductive that is connected to both battery terminals. Standing in a puddle has nothing to do with it, unless the battery is somehow connected to the puddle.
So, suppose you take a 36V and touch one finger from each hand to both terminals, so that the path is through the chest. What is likely to happen?
You will likely feel a "tingle", if there is enough current flow you may get burns at the contact point. It could also cause the heart to stop - batteries are DC. DC is actually better than AC in this regard, because AC can cause damage to the heart muscle, while DC just clamps it and makes it stop. If you get zapped with DC and get medical treatment in time, it's often possible to revive a person. In contrast, with AC the heart may well be damaged beyond repair.
Note also that higher voltage and current are more dangerous and can cause more damage.
The lowest recorded electrocution in the literature is at 18 Vac equates to roughly 25 V peak - believe this was a broken skin situation .
Let us call the lowest number for unbroken skin impedance at 36 V (ac peak or dc) 400 ohms. iA test number is 417 ohms hand to hand at 1 kHz for full hand immersion in salt water. (Don't ask how I know for sure, let us just say I already got into trouble once for 'human experimentation' on myself and DW.) Let us use the 417 ohms reduced to 400 ohms for safety margin. DC resistance is higher, about 690 ohms, but let's use the 400 ohm number for worst case.
The threshold for the most sensitive (0.1%) people for electrocution is around 20 mA, a level most people first experience muscle contraction (let - go) effects at. 50 mA is a 50% electrocution number often used.
SO, 36/400 = 9 mA, zero electrocution hazard for no risk IF YOU HAVE UNBROKEN SKIN - no cuts or splinters. I once receive a fairly severe shock when I had a metal splinter in a finger I did not realize I had.
That said, the startle reaction from very sensitive people can be less than the threshold of sensing a shock for most people, less than 2 mA.
Thus, looking at an absolute worst-worst case scenario, someone wearing shorts inserting a newly charged battery on an aluminum ladder while being sprayed with salt water, having one battery terminal in contact with the ladder, their leg against the ladder, and touching the other terminal with a tightly gripped tool, they conceivably could get a startle shock and fall off the ladder.
OTOH, with dry fingers I can lightly touch even 120 V 60Hz and not feel anything.
In light of the way you phrased your question, 'should workers be aware', the answer is yes if they know they are extremely sensitive to electrical shock (or have no idea of their tolerance level) or especially if they have an open cut .
Hope that helps.
I'm not going to have e-mail for a few days, but I have a collection of anecdotes on shock for as low as 24 Vac (including from an informal survey of this board) I can share if you e-mail me.
These word documents are some of the anecdotes from this site and HVAC-talk that I've compiled inthe past.
From the thread references, you can find the rest on-line.
As a general rule, anything below 50V is "safe". There are of course exceptions, but they require some fairly oddball circumstances. In particular, you have to get the juice going across your heart, and since the terminals are so close together you're unlikely to have one hand on each with soggy wet hands -- the situation that could present a slight risk.
A bigger danger is tossing a battery in a toolbox and having it short out and cause a fire. It's wise to always put spares in some sort of case or holder, both to protect them and to prevent the possibility of fire.
Sorry - I gotta ask - Are you Larry Haun the author?
Hi Matt,
Yes, I'm the writer. I will have an article in FHB magazine next year on tools we use to install fiber cement siding. Take care, larry
I have to take a minute to thank you for your articles and books that had winder stairs in them.
I was approached to frame 6 sets of them and had never framed them before.
I took the basics you provided and built them easily, even built a set of 180 degree winders.
I can't thank you enough for showing me something new.
Matt
Matt,
Always good to know that what I have written is helpful. I am still building---Habitat houses these days. No winders in these houses. larry haun
Yes, I have one of your books and I think a few tapes too. Thanks for joining us. If I'm not mistaken I remember "seeing" you around here some years ago too.