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At a safety class the instructor told us that we...

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Dear Tom and Ray:



At a safety class, the instructor told us that we could be electrocuted while jump-starting a car if we touched the battery terminals. I found this very difficult to believe, especially since I had touched both battery terminals at the same time many times before. I bet the instructor $1,000 that I could walk out to the parking lot, touch the terminals on a car battery and live to take his cash. He declined dismissively (as if he was certain to be saving my life). Then a co-worker, who happens to be a nuclear physicist, sided with the instructor, insisting that he had read accounts of people being electrocuted by a car battery. But then again, he thought car batteries were 24 volts. I know that car batteries can be dangerous because of the heat associated with a high-current short circuit and a chemical explosion, but do we really need to worry about a life-threatening shock from them? -- Rob

RAY: Well, I have tried -- many times -- to get my brother to electrocute himself on car batteries, but I've never had any success.

TOM: He's always telling me, "Put one finger here and one finger there, and let me know if you feel anything." So THAT'S what you were up to!

RAY: Well, based on my years of observation and, obviously, failure, I don't believe you can electrocute yourself by touching both terminals of a 12-volt car battery. Twelve volts just isn't enough electrical pressure to overcome the resistance of the human body. So, in my opinion, the instructor and the physicist are both wrong. And I'm surprised about the instructor.

TOM: HOWEVER -- and this is a big however -- batteries are dangerous for other reasons. If you connect the two terminals together with a metal object, like a wrench, you'll short out the battery, melt the wrench and likely cause sparks to fly. Then you'll basically recreate the Hindenburg disaster in your driveway (note for younger readers: kaboom!).

RAY: Plus, there are lots of other things under the hood that CAN hurt you. Power from the battery travels to the coil, where it is boosted to 50,000 volts or more and then sent to the spark plugs. And 50,000 volts is enough to give you a zap you won't soon forget.

TOM: So while batteries (and things under the hood in general) need to be respected because of the power they transmit, we don't think that simply touching the battery terminals is enough to electrocute you. But don't try it at home, Rob (or anyone else). Remember, we're wrong a lot.
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