There are many factors that influence the severity of the electrical shock that results when a person comes into contact with a live conductor. These factors include voltage, current, waveform, whether it’s alternating current or direct current, the frequency of AC, and the length of time of exposure.
In addition, the impedance of the human body has a direct effect on the severity of the shock. The average person has an impedance of about 1000 ohms from one hand to the other, but this can vary depending on body shape, age, weight, sex, the path of the current through the body (if it’s other than hand to hand), the amount of clothing worn, and the amount of moisture involved.
It doesn’t take much current to make a human heart go into defibrillation. The body’s own natural electrical pulses that pace the heart are on the order of a millionth of an amp. As little as 100 to 300 milliamps passing though the heart can interrupt its natural rhythm and cause it to go into fibrillation.
When that happens, the heart flutters and can’t deliver the necessary oxygen to the blood, eventually causing death. Fortunately, we have a certain amount of control over the impedance we present to a power source.
We can increase our impedance by wearing protective clothing, including V-rated gloves, rubber-soled shoes, long pants and shirt made of cotton (rather than nylon or other synthetic fabrics that will melt to the skin), a hat — preferably a hard hat or some other insulating material — and thick socks.
We can take off dangling jewelry like necklaces or earrings, and carry a carpet to stand on in the event our work environment is bare concrete. We can use V-rated tools and we can ensure that we are not standing in water when we’re working on live electrical equipment.
In addition to trying to increase our impedance as much as possible, it also helps to be aware of the effects of the path that current takes through the human body. The most damage is caused by electricity passing through the lungs, heart, and brain. But the path of the highest impedance is from one hand to the other.
By taking precautions and working intelligently, we can lower our risk of electrocution. According to Ohm’s law, if we can raise our impedance, then we will lower the current passing through our body in the unfortunate event that we come into contact with a live circuit. If we succeed in lowering the current then we have a better chance of survival.
Effects of Electrical Current
Electrical current is what can cause damage to the human body. Its effects range from slight perception to heavy burns. Most people start to perceive current at about 0.2 to 0.5 milliamps. The “startle” current is considered 0.5 milliamps.
Although this level of current will most likely not cause any serious damage, if you’re walking a truss or hanging off of a ladder it could be a very serious situation. At a level of 10 milliamps, 1.5% of men, 40% of women, and 92.5% of children contract their muscles to the point where they can’t let go. At 20 mA, 92.5% of men and 100% of women and children can’t let go.
At 30 mA, no one can let go. The maximum current level allowable for every person to be able to let go is 6 mA, which is the trip value of a certain class of ground fault circuit interrupters (GFCIs) that are designed to protect human life.