Health Effects of Electromagnetic Radiation

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The health effects associated with overhead power lines and household electrical appliances have been one of the most controversial topics debated among scientists (1). Strong magnetic forces are associated with high currents, such as those near thick wires and equipments which draw high currents. A current passing through a wire creates a magnetic field that encircles the wire (Ampere’s law). The magnetic field’s strength is highest closer to the wire and drops off as the square of the radial distance from the wire. It is very difficult to shield the magnetic field.

Table 1. Health Effects of Electrical Shocks*
Current through the body trunk Effect on average human
< 1 mA No sensation
3-10 mA Tingling. Person can let go.
10-30 mA Muscle contraction, person cannot let go
30-50 mA Painful. Severe muscular contractions. Breathing difficult
50-100 mA Ventricular fibrillation, probable death
> 100 mA Fatal
* Center for Disease Control & Prevention website

Strong electric fields are associated with the presence of strong electric charges, such as around high-voltage equipment. A person standing underneath a power line experiences an electric field perpendicular to the ground. The closer the power line is to the ground and the higher its voltage, the higher the electric field’s strength. For example, a single 115 kV cable running 15m above the ground causes an electric field of E = 500 V/m near the ground. Depending on the frequency of the AC line, the direction of the field lines reverses 50-60 times per second, causing rapid changes in the direction of the electric field through a body and exposing it to ionization radiation. Unlike magnetic fields, electric fields can be shielded by conductors such as metals. We discussed the effect of ionizing radiation and its ability to cause symptoms from headaches to cancer in detail in nuclear radiation. Although the connection between power line fields and cancer is an area of continuing research, so far there are no scientific studies that point to a consistent, significant link between cancer and power line fields. A summary of health effects associated with electrical shocks is given in Table 1.


Physiological Effects of Electricity

When current passes through living tissue, it experiences resistance and dissipates its energy as heat. Depending on the magnitude of current and tissues involved, electricity can manifest itself in several forms, from low heat and slight tingling to severe burns, paralysis, and even death.

The most significant hazard associated with electric shock is its damage to a person’s nervous system. The nervous system consists of a series of nerve cells called neurons that are responsible for coordinating all of the body’s movements – from the beating of the heart to the blinking of eyes – by passing information from various organs to the brain. This is done by releasing chemicals called neurotransmitters which generate tiny electrical signals that can travel the nervous system. Currents from external sources can be strong enough to override the neurotransmitters, preventing them from carrying out their normal functions. If this happens, volitional signals cannot be transmitted and affected muscles will involuntarily contract. This effect is particularly dangerous when a person touches a bare electrical wire. Fingers have the least resistance to current flow and can easily bend involuntarily, clenching into a fist that grabs the wire. The victim becomes immobilized and unable to let go of the wire, making the shock even more dangerous. The involuntary contraction of muscles is called tetanus in medical terminology. The condition persists as long as the current flows.

Shock Severity

The length of time, the type of tissues involved, and the magnitude of the current determine the severity of hazard associated with electrical shock and the extent of damage it causes. The best way to reduce the electrical shock from a live circuit is to add resistance to the path of the current. Rubber gloves and boots increase the resistance, thus reducing the current for the same voltage difference. Grounding makes an excellent means of protection by providing a path of least resistance through the ground (and not the body). The current passing through the victim’s body is determined by the body’s resistance, which varies greatly from one organ to another and whether the skin is dry or wet. For the same voltage difference, the current passing through wet skin or a sweaty hand will be higher. When the path of current is from hand to hand or from hand to foot, vital organs such as the heart, lungs, or spinal cord are affected, and the shock effect is the most severe.

Question: A common phrase often heard in regard to electrical safety is, “It’s the current, not the voltage that kills.” Why then, are we often warned of the danger of high voltage?

Answer: Strictly speaking the sentence is correct. It is the current that is dangerous. The voltage only pushes the current through bodily resistance. The question is where do all those currents come from? High voltages mean the potential for creating high currents for a given resistance path through a body - higher voltages can be directly translated into higher currents.

Question: When is the effect of electrical shock most severe? With a 120 V or a 220 V? With direct current (DC) or alternating current (AC)?

Answer: If everything else is the same, higher voltages result in higher currents; therefore voltages in the US outlets are safer than those in Europe. It is difficult to quantify whether DC or AC is more dangerous. Direct current is generally considered to pose less of a shock hazard, but it produces more severe burns. A person shocked with an alternating current is more likely to go into heart fibrillation.

Figure 1 Current diagram.
Figure 1 Current diagram.

Example 13-10: In the diagrams to the left, determine which instance provides the safest situation for the bird or person involved.

Solution: For current to flow through a circuit, an electrical potential is required. A bird sitting on the wire experiences practically no voltage drops between its feet and therefore is immune to potential danger, no matter how high the current is. On the other hand, if the bird were to touch both the high- and low-voltage cables at the same time, it would then draw a lethal current through its body. To assure birds’ safety, the separation distance between the power cables is chosen to exceed the wingspans of most birds.

This is not true for the boy, however. In diagram (a) the boy holds the bare wire with one hand. Since he is standing on the ground (which by convention has zero voltage), there is a voltage difference between his hand and foot. As a result, electricity flows through his hands and body and eventually reaches his feet, closing the circuit and shocking the boy. The downed power line in diagram (b) causes a large electric potential between the points where wire touches the ground and the nearest pole where the transmission line is grounded. Thus there is a voltage differential between the feet of the boy standing somewhere in between, and he would be shocked. Probably the best way to avoid shock is to keep your feet close together, stand on one leg, or run away from the power line. Running has the same effect of having one foot on the ground, preventing a large voltage drop between the victim’s feet.

Example: In the example above, would it make a difference if the boy were bare-footed? What about if he touched the wire with both hands?

Solution: If the boy wears shoes with thick, insulated rubber soles, then he is protected from electric shocks. The problem arises if any moisture, dirt, or other conducting substances (such as a metallic strip) provide a path of least resistance and allow the electricity to bypass the sole directly to the body. Leather soles provide much less resistance and are not nearly as effective. Some ground surfaces are better insulators than others. Asphalt contains some oil, which makes it a better insulator than most dirt, concrete, and rocks.

If the boy holds the wire with both hands, the contact area doubles and two parallel pathways are available for the current to flow. The overall resistance is only one-half of the resistance from one hand, and twice as much current would flow though the body. It is a good practice to keep one hand in a pocket when working around electrical devices!

Example: A bird is sitting on a piece of bare copper wire carrying 100 amperes. It is estimated that the copper cable has a resistance of 20 ohms/kilometer. Assuming the bird’s feet are 10-cm apart, what is the voltage potential established through the bird’s body?

Solution: The resistance between the bird’s feet is calculated as 0.10 m x 20 ohms/1000 m = 0.002 ohms, and the potential difference is DV = I x R = 100 x 0.002 = 0.20 volts; this is not enough to do any harm! As mentioned earlier, power cables are often setup so the separation between the high and low-voltage cables exceeds the bird’s wingspan.


(1) For more information on effects of EMF exposure on health see the Word Health Organization’s International EMP Project (

(2) Toossi Reza, "Energy and the Environment:Sources, technologies, and impacts", Verve Publishers, 2005

Further Reading

Bureau of Naval Personnel, Basic Electricity, Dover Publishing Company.

The Environmental Effects of Electricity Generation, IEEE, 1995.

The Electricity Journal, Direct Science Elsevier Publishing Company, This journal addresses issues related to generating power from natural gas-fired cogeneration and renewable energy plants (wind power, biomass, hydro and solar).

International Journal of Electrical Power and Energy Systems, Direct Science Elsevier Publishing Company.

Home Power Magazine (

External Links

Federal Energy Regulatory Commission (

Energy Information Agency, Department of Energy (

California Energy Commission (

National Council on Electricity Policy (

Southern California Edison (

Pacific Gas and Electric (