Frequently Asked Questions Electric and Magnetic Fields
What are electric and magnetic fields?
All of us depend on electricity on a daily basis. We rely on electricity to meet basic needs such as heating, cooling and lighting our homes. And we depend on electricity to meet the transportation, communication and industrial requirements of a modern society. Electric and magnetic fields, often collectively referred to as EMF, are natural occurrences as a result of our use of electricity.
Wherever an electric current is present, fields of magnetic force occur. For example, the earth has a large magnetic field, which makes compass needles point north, and the human body generates its own electric current that is necessary for life. Because electricity is so common in daily life today, most of us are in contact with electric and magnetic fields virtually all of the time. Examples include home wiring, cars, water pipes, kitchen appliances, televisions, computers, hair dryers, electric clocks and utility power lines.
How do these fields behave?
Electric fields are created by voltage. The higher the voltage, the stronger the electric fields. You will find an electric field near any electrical appliance that is plugged in, even if it is not operating. Electric fields are strongest closest to their source.
Magnetic fields are created by current or electricity flowing through a wire. Magnetic field strength increases with current, so you will find a stronger magnetic field near an appliance when it runs on “high” than when it runs on “low.” An appliance must be plugged in and operating to create a magnetic field. Magnetic fields are also strongest close to their source.
Where might I find electric and magnetic fields?
Electric and magnetic fields are found everywhere electricity is used, such as personal computer terminals, televisions and other household appliances. The magnetic fields are measured in milligauss. Magnetic fields associated with appliances are typically stronger than those fields found near power lines.
Can these fields be blocked?
Electric fields can be blocked by most objects such as trees, the ground, buildings and other objects. However, magnetic fields pass through most objects. This is one reason why burying power lines will not necessarily eliminate magnetic fields.
How do you measure electric and magnetic fields?
The strength of electric and magnetic fields can be measured with special instruments. Electric fields are measured in units of volts per meter (abbreviated V/m) with an electric field strength meter. Magnetic fields are measured in units of milligauss, (abbreviated mG) with a gaussmeter. Most scientific research and public issues have focused on measuring magnetic fields. Therefore, we will be referring more frequently to magnetic fields. The electric field's strength is determined by the “push” or voltage necessary to make the electricity move.
The higher the voltage, the greater the field produced. Current does not have to be flowing in an object for an electric field to exist. Thus, a stereo or toaster that is plugged in, but not operating, may still produce an electric field.
What do these measurements really mean?
Although new technology has made it easier to measure EMFs, it is still very difficult to relate these measurements to human exposure. Measurements vary from moment to moment, depending on the current flow, the type of appliance and a person's position in relation to the source of the fields. Interpreting measurements and setting guidelines for exposure levels are difficult, and there is still no consensus as to any health effects resulting from EMFs, let alone whether such effects are related to stronger or weaker fields. It's also not clear whether brief, high-level fields from appliances such as hair dryers have more impact than continuous low-level fields from power lines, wiring or other sources.
What are some typical magnetic field readings?
Typical 60 hertz magnetic fields measured at various distances. Magnetic fields are measured in milligauss (mG).
|Typical items in the home||1 inch||1 foot||3 feet||Maximum|
|Electric can opener||5000.0||470.0||24.0||30,000|
|Transmission lines*||Under line||Edge of right of way||50 ft. from edge|
|44,000 volts||1.0 - 25.0||0.2 - 2.5||0.1 - 1.0|
|100,000 volts||2.1 - 19.3||0.6 - 3.4||0.3 - 1.9|
|230,000 volts||4.5 - 29||1.9 - 6.4||1.0 - 3.5|
|525,000 volts||17 - 40||6 - 15||2.4 - 4.0|
|Distribution lines*||0.1 - 35|
|Substation||Magnetic fields from the equipment in a substation, measured at the fence, are generally negligible. However, readings at the fence can reflect the magnetic fields from the power lines entering and exiting the substation and generally do not exceed readings in this table for distribution lines.|
|*These are typical readings under normal operating conditions at moderate load.|
What kind of EMF research has been done?
Two types of studies are being done: laboratory studies and epidemiology studies. Millions of dollars are being spent worldwide on EMF research and more conclusive information is expected in the next few years. To be able to put research results in perspective, it is helpful to understand the strengths and weaknesses of each type of study.
Laboratory studies primarily involve exposing cells, tissues and animals to either electric or magnetic fields under a variety of controlled conditions. These studies allow research to closely control exposure to EMF and provide information about the small-scale changes EMFs may cause. Most emphasis to date focuses on the changes caused by magnetic fields. However, laboratory studies have not shown how or if these changes affect human health. Nor have they been able to precisely duplicate the types of EMF exposures that people experience throughout the day.
In EMF epidemiological studies, researchers try to establish whether there is a statistical association between selected groups of people with certain types of EMF exposure and certain kinds of disease. However, these types of studies cannot establish a clear cause-and-effect relationship between EMFs and disease. This is because real-life studies cannot rule out other possible explanations for health effects such as diet and lifestyle and because it is difficult to discover what past exposures to EMFs and other factors have been.
What do you mean by “association"?
Some studies have suggested an “association” between EMF and some types of cancer. An association is different from a “cause and effect.” Association means that two or more events can be joined or linked together. This linking of events does not necessarily mean that the association is valid. Cause and effect means that if one event occurs (cause) another event (effect) will occur a percentage of the time. The most common analogy of an association is this:
ASSOCIATION: A rooster crowing in the morning will cause the air temperature to rise several hours later.
There is strong statistical association between a rooster crowing and the air temperature rising. We know that this occurs a very high percentage of the time. However, the association, while statistically linked, is incorrect.
Therefore, there is NOT a cause and effect. The sun rising (cause) is the common event that results in the air temperature (effect), not the rooster crowing. Some studies thus far have tied a slight association to EMF and cancer. No common cause has been directly related to the effect. Scientists are trained to sort out true causes from observed associations such as that above. This is especially important in the EMF research now under way.
Have there been recent studies on EMF?
Some laboratory studies have suggested that EMFs may cause small, sometimes reversible changes in cell reproductions, rhythms, communication and growth. Research is being done to confirm these results and to determine how these changes occur and whether they have implications for human health.
Review of Studies
In the early 1970s, public concern began to surface over possible health effects associated with electric and magnetic fields. Since then, hundreds of studies have been completed or are under way. Many of the studies have dealt specifically with magnetic fields that exist around appliances or power lines. To date, none of these studies have shown a cause and effect relationship between EMF and human health.
The weight of reliable evidence suggests that long-term risk to public health, if it exists at all, appears to be very small. According to a number of science and health experts researching the issue, including panels convened by the World Health Organization, the National Academy of Sciences and the American Institute of Biological Sciences, there exists no persuasive scientific evidence that electric and magnetic fields can lead to public health problems. The following is a brief summary of several major EMF studies completed in recent years:
A Swedish residential study released in 1992 is among the largest and most detailed investigations of magnetic fields and cancer. The researchers state that there is an association with estimated exposure and some cancers in this study. However, they were unable to find an association between measured magnetic fields and cancer.
A Finnish EMF/childhood cancer study was released in 1993 in the British Medical Journal that involved a cross-section of the entire country's population. It concluded that residential magnetic fields of transmission power lines do not constitute a major public health problem regarding childhood cancer. A Greek childhood leukemia study conducted by Harvard University School of Health, University of Crete, University of Athens and two children's hospitals was released in 1993. The study reports no EMF risk. (There were no associations reported for homes within 100 meters of substations.)
In 1993, Southern California Edison and the University of California examined electric and magnetic field exposure and health records of more than 36,000 male electric utility employees. The study found no increase in overall cancer rates among electric utility workers exposed to fields. The study also found no increase in leukemia or brain cancer rates.
In 1994, the relationship between magnetic field exposure and health records was studied on more than 223,000 male electric utility workers at Canadian and French utilities. Researchers could not identify any cause-and-effect relationships between cancer and exposure to magnetic fields. When the research was broken down into smaller categories some possible relationships were found, but the smaller sample size caused an increased margin of error in the results.
In 1995, Dr. David Savitz with the University of North Carolina School of Public Health also studied the possible health effects of magnetic fields and male utility workers. The study concluded that overall levels of mortality from all causes of death, including brain cancer and leukemia, were lower among the electric utility workers studied than in the general U.S. population. Preliminary information from the study did suggest, however, that workers exposed to high levels of magnetic fields may face a slightly higher risk of brain cancer than similar workers with lower exposures. The study did not find any relationship between magnetic fields and leukemia. Both of these finds are in conflict with earlier studies.
In February 1996, the American Cancer Society released a summary report of their review of the scientific studies. They state “to date, no form of electromagnetic energy at frequency levels below those of ionizing radiation (x-rays) and ultraviolet radiation has been shown to cause cancer."
In October 1996, the National Research Council, under direction of the U.S. Congress, released a review of the scientific literature. They state “based on a comprehensive evaluation of published studies relating to the effects of power frequency electric and magnetic fields on cells, tissues, and organisms, the conclusion of the committee is that the current body of evidence does not show that exposure to these fields presents a human-health hazard."
The National Institute of Environmental Health Sciences (NIEHS) concluded in 1999 that the evidence for a risk of cancer and other human disease from the electric and magnetic fields around power lines is “weak.” They stated that “the results of the EMF-RAPID program do not support the contention that the use of electricity poses a major unrecognized public-health danger.” NIEHS Director Kenneth Olden, Ph.D., said, “The lack of consistent, positive findings in animal or mechanistic studies weakens the epidemiological findings. For that reason, and because virtually everyone in the United States is routinely exposed to EMF, efforts to encourage reductions in exposure should continue.” As with similar epidemiological research on EMF and cancer, these studies add to the growing body of knowledge on EMF and possible health effects.
What about studies of people, particularly studies involving cancer?
Much attention has focused on the incidence of cancer among people living or working near electric and magnetic fields. Researchers in Colorado, Washington, Rhode Island, England, Canada, Denmark and Sweden have completed studies on the statistical incidence of cancer. Some suggest a possible relationship between cancer and the proximity of outdoor power lines; the others found no such relationship. However, none of the researchers found a direct link between actual EMF exposure and cancer incidence. Studies of people who work around electric equipment also have been inconclusive. Some studies suggest that electric and telephone lineworkers, electricians and aluminum workers have a slightly higher risk of cancer while other studies find no evidence of increased risk.
Have any of the laboratory, childhood or occupational studies established a cause and effect relationship between EMF and cancer?
No. The researchers would like to find a way to separate other factors such as exposure to heavy traffic, air pollution or chemicals that might play a role in increased cancer rates reported in EMF epidemiological studies. For instance, workers exposed to EMFs may also be exposed on the job to chemicals that could cause cancer. Study findings may also be due to the small sizes of the groups studied.
Are there harmful health effects?
The use of electricity has increased greatly in the last 40 years, but there has been no corresponding significant increase in childhood leukemia or any of the other cancers suggested by epidemiological studies. The consensus among health professionals and scientists studying the issue is that no firm conclusions can be drawn. Based on this fact, and on the research to date, some researchers believe that if EMFs are shown to cause health effects, the risk of these effects will probably be comparatively small.
Voluntary risks are more accepted.
Individuals will typically accept great risks that they choose for themselves if they think that related benefits are worth it, but still reject even the slightest risks they feel are imposed on them. For example, more than 3 million people are killed or injured in motor vehicle accidents each year but people continue to drive. Although the risks related to EMFs remain unproven, people may be unwilling to accept those risks because they believe that their exposure is not a matter of choice.
Deciding what is right for you.
We all face risks in life all the time and probably have our own ways of determining what actions are sensible. Do you always spend the extra time it takes to buckle your seatbelt? How much time and money do you invest in fire safety around your home? Like these decisions, the EMF issue requires that we gather information, weigh the risks and do what makes the most sense to us. The aim of Duke Energy is to provide you with the information you need to make that informed decision.
Several states have set guidelines for power line design and location. But because there is no consensus on the issue, most states and regulatory agencies recommend that further study occur before health-based standards are set or high expenditures are made to limit EMF levels from power lines and electrical equipment. In the absence of widespread government standards, it becomes a matter of personal responsibility to weigh the potential risks associated with EMFs and to determine your response.
Are EMFs like microwaves and x-rays?
No, they are not the same although they are all forms of electromagnetic energy. EMFs from electricity are a much lower frequency and therefore have lower energy than microwaves or X-rays. When you use a microwave oven, the energy passes through materials containing water, converting the energy to heat energy. This heat is absorbed by the materials making your food or liquid hot. X-rays are much stronger. The energy in X-rays is strong enough to break apart the molecules that contain genes. Excessive X-ray exposure can lead to mutations and cancer. While X-ray exposure has its risks, so do the conditions that X-rays are meant to diagnose. This is why you and your doctor should make careful judgments about when you have X-rays taken. EMFs do not have enough energy to break apart molecules like X-rays do. And although EMFs can cause heating in substances, this heat is barely detectable. Normally occurring temperature changes in human cells are greater than the temperature changes EMFs can produce. Some laboratory studies have suggested EMFs may produce small changes in human cells. These changes are yet to be understood.