When I was about 5 years old, my grandfather taught me an important lesson about electrical safety. He took me to see the electrified fence he had just built around his backyard vegetable garden. As we approached it he plucked a blade of grass from the ground in front of the fence, put it in my hand, and had me touch the grass to the metal fence.

Instantly I felt the tiny current travel down the grass and into my arm. It wasn't a constant flow. It was a tiny tingling pulse: on, off, on, off. "The electricity in this fence isn't very strong," my grandfather explained to me. "It's just enough to keep animals away. But if it were stronger it would hurt you." As my fingers tingled on the blade of grass, I understood exactly what he meant. I dropped the grass and my pulse returned to normal. With that valuable lesson in electrical safety in mind, I never touched that fence again. (Of course all of this was more than 40 years ago, and my grandfather's teaching technique would undoubtedly be frowned upon today.)

Electricity is all around us — not to mention inside of us, where it keeps our hearts pumping and our muscles moving — but despite its prevalence in our lives, it is often poorly understood and all-too-often dangerous. According to the Electrical Safety Foundation International, there are more than 30,000 non-fatal shock accidents every year. Electrical safety fatality statistics are harder to come by, but by some estimates at least 600 people die of electrical accidents in the U.S. every year. And it doesn't take much: The same amount of energy it takes to illuminate a tiny Christmas tree light could also be enough to kill you in the right conditions.

How the body conducts electricity

So why is electricity so dangerous? Electricity flows from one point to another along anything that will conduct it. One of the better conductive substances for electricity is water, which happens to represent about 70 percent of the human body. But even with all of that water inside of us, electricity doesn't flow through the human body unobstructed. It encounters resistance along the way, which causes some of the energy from the electric current to turn into heat. That heat from resistance causes one of the dangers of electricity: burns.

Beyond that, electricity can also mimic or override the natural signals going from nerve to nerve in our body, causing muscle contractions. Even at small levels, this can cause muscles to painfully lock into place. This makes it harder to let go of whatever is delivering the current, increasing the risk. As the Occupational Safety & Health Administration (OSHA) puts it, "low voltage does not imply low hazard" because longer exposures are more dangerous. These muscle contractions can also cause a person to fall and be injured beyond the direct effects of the electricity.

As current levels increase, either in the amount of electricity or the length of time of exposure, muscle contractions can worsen, the respiratory system can seize up, blood vessels can constrict and the heart can begin to pump in an uncoordinated manner. Much more exposure can cause cardiac arrest, in addition to other damage and burns.

How much electricity can a person stand?

The amount of electricity a person can withstand depends on their health, the amount of the electrical current and the length of time for the exposure, as well as other environmental factors such as the presence of moisture (which is why using a hair dryer in the shower is all that much more dangerous). The danger also depends on where the electricity enters your body and where it exits. If electricity enters your body through your left hand, it's probably going to try to exit into the ground through your left foot, passing right through your heart along the way.

The difference between a mild electric tingle on your fingers isn't all that significant. You can feel the effects of electricity as low as 1 milliampere. Just 100 times that much can cause heart fibrillation in as little as three seconds. That's a tiny fraction of the electricity it takes to power the average toaster.

So how do you keep yourself protected from the dangerous effects of electricity? The National Fire Protection Association offers several tips on electrical safety, especially for families with young children. OSHA offers several more tips, including this basic one: Always assume that any wire you see contains enough electricity to kill you. As my grandfather taught me years ago, it's better to look than to touch, and it's best to always stay safe.

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