Q & A About EMF Electric and Magnetic Fields

22 мая 2014 | Author: | Комментарии к записи Q & A About EMF Electric and Magnetic Fields отключены
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Electric and Magnetic Fields with the Use of Electric Power

Electric power is a fact of in America, a familiar miracle. have come to take for the simple flip of a switch turns night into With electric power, come certain precautions are also well known. power lines, household and appliances can cause serious from electric shock if improperly.

Recently, a new question has about the electric power we all on: Does it have anything to do cancer?

Some epidemiological have suggested that a may exist between exposure to electric and magnetic fields and certain types of cancer, leukemia and brain cancer. studies have found no link. Laboratory researchers are how such an association is biologically At this point, there is no consensus about the EMF issue-except a agreement that better is needed.

A national EMF research is under way, and major results are expected in the next few

This article provides answers to common questions the possible health effects of First, we define some electrical terms, describe and discuss recent scientific We then describe what the is doing to address public about EMFs.

Next, we questions people have their own exposure to EMFs. We tell you how to obtain more information about these

Electric Power Basics

article uses six basic terms- conductor, current, load, power, and circuit. The is the wire you see between power or towers; it carries the electricity. is the movement of electrons in the conductor.

is the electric force that current in a conductor. Load is the power needed by homes and When a conductor energized voltage is connected to a load, a is completed, and current will

Electric Power Facilities

are two basic types of power transmission lines and distribution Transmission lines are high-voltage lines. The high voltage electric power to be carried over long distances electrical generation facilities to near urban areas.

In the States, most transmission use alternating current (AC) and at voltages between 50 and 765 kV (lkV or = 1000 V).

Utilities use lower-voltage lines to bring power sub-: ;0iV stations to and homes. Distribution lines at voltages below 50 kV. For residential these levels are further to 120/240 V once the power its destination.

Electrical substations many functions in controlling and power on an electrical system. different types of equipment may be depending on the functions of the particular For example, transformers change the voltages used by transmission to the lower voltages used by lines.

Circuit breakers are to turn lines on and off.

Current and Direct Current

that operate either batteries or by plugging into the wiring usually come with an AC /DC switch. If switched to AC, the uses electric power flows back and forth or at a (U.S.) rate of 60 cycles per (60 hertz, or Hz). If DC (direct is chosen, current flows one way the batteries to the appliance.

AC fields weak electric currents in objects, including humans; DC do not, unless the DC field in space or time relative to the in the field. In most practical a battery-operated appliance is unlikely to electric current in the person the appliance. Induced currents AC fields have been a for research on how EMFs could human health.


Q. What are EMFs?

A. Power electrical wiring, and appliances all electric and magnetic fields. are invisible lines of force surround any electrical device. and magnetic fields have properties and possibly different of causing biological effects. that while electric are easily shielded or weakened by objects (e.g. trees, and human skin), magnetic are not.

However, both electric and fields weaken with distance from the source.

though electric and magnetic are present around appliances and lines, more recent and research have focused on health effects of magnetic This is because epidemiological have found associations increased cancer risk and configurations, which are thought to be for magnetic fields. No such have been found measured electric fields.

Q. is power-frequency EMF and how does it compare to types of fields?

A. The electromagnetic (right) covers an enormous of frequencies. These frequencies are in cycles per second (i.e.

Electric power (60 Hz in North 50 Hz in most other places) is in the range, which includes below 3000 Hz.

The higher the the shorter the distance between one and the next, and the greater the amount of in the field. Microwave frequency with wavelengths of several have enough energy to heating in conducting material. higher frequencies like cause ionization-the breaking of bonds, which damages material.

In comparison, power fields have wavelengths of than 3100 miles km) and consequently have very low levels that do not cause or ionization. However, AC fields do weak electric currents in objects, including people and

Q. Doesn’t the earth produce

A. Yes, the earth produces mainly in the form of DC (also static fields). Electric are produced by thunderstorm activity in the Near the ground, the DC electric averages less than 200 per meter (V/m).

Much fields, typically about V/m, occur directly electrical storms.

Magnetic fields are thought to be by electric currents flowing within the earth’s molten The DC magnetic field averages 500 milligauss (mG). This is larger than typical AC power magnetic fields, but DC do not create currents in objects in the way AC fields do.

Q. What happens I am exposed to EMFs?

A. AC fields weak electric currents in the of people and animals. This is one why there is a potential for EMFs to biological effects. As shown on the currents from electric and fields are distributed differently the body.

The amount of this even if you are directly beneath a transmission line, is extremely (millionths of an ampere). The current is too to penetrate cell membranes; it is mostly between the cells.

from 60-Hz EMFs are than natural currents in the such as those from the activity of the brain and heart. scientists argue that it is impossible for EMFs to have any effects. Other scientists that, just as a trained ear can up a familiar voice or cry in a crowd, so a may respond to induced current as a lower in intensity yet detectable through the background noise of the natural currents.

Numerous studies have shown biological effects can be caused by to EMFs (see Biological In most cases, however, it is not how EMFs actually produce demonstrated effects.

Strong fields, such as those beneath large transmission can cause hair on your head or arms to vibrate at 60 Hz. This is felt by some as a tingling sensation. EMFs transmission lines can also in circumstances cause nuisance from voltages created by on objects like ungrounded fences.


Q. How do scientists study possible of EMFs on people?

A. They use a type of research epidemiology-the study of patterns and causes of diseases in human Epidemiologists study short-term such as outbreaks of food and long-term diseases such as and heart disease. Results of studies are reported in terms of associations between various and disease. The challenge is to discover the statistical results indicate a causal association.

This assessing possible effects of factors confounders that affect study results. A significant finding is one in which are 95% confident that an association However, a statistically significant does not necessarily prove a association.

Usually, supplemental are needed from studies of animals before scientists can that a given factor is a of disease.

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The language of epidemiology can to the uninitiated, more precise it actually is. An odds ratio example below) is an estimate. must calculate, along the odds ratio, the range which they are confident this estimate is reliable. size is a key factor in this

The smaller the sample, the less the information.

How Epidemiologists Conduct Studies

The Process

A list of with a particular disease is These are the cases .

A list is of people who similar to the cases, but who do not the disease. These are the controls .

The of cases and controls who were exposed to factor X are estimated. is often one of the most difficult of the study because exposures often occurred many in the past.

The exposure ratio of the is compared to that of the controls. If the are the same, there is no association factor X and the disease. If the cases a higher ratio, there is a association . and factor X may be the cause of the

If the cases have a lower ratio than the controls, is a negative association . This suggest that factor X may protect people from the


Here are 2 examples of outcomes of a study of a potential factor X, based on 300 cancer and 300 controls:

If 71 cases were to factor X and 229 were not exposed, the exposure ratio = 71/229 = If 71 controls were also the control exposure ratio is 0.31. Dividing the case ratio by the control ratio the odds ratio (OR) . called the relative risk = 1.00). An OR of 1.00 means the odds that the cases exposed to factor X was the same as for the

Therefore, in this example, is no association between factor X and

Now suppose that 110 of the total 300 were exposed (ratio = = 0.58), and 71 controls were (ratio = 0.31). The OR is 0.58/.031 = If the OR is above 1.00, there is a association between factor X and the

In this example, people to factor X had an 87% increased risk of cancer.

Q. What have the of cancer in people living power lines found?

A. To 14 studies have analyzed a association between proximity to lines and various types of cancer. Of these, eight reported positive associations proximity to power lines and form(s) of cancer. Four of the 14 showed a statistically significant with leukemia.

The first to report an association between lines and cancer was conducted in in Denver by Dr. Nancy Wertheimer and Ed They found that who had died from cancer 2 to 3 times more likely to lived within 40 m (131 ft) of a power line than the other children studied. to magnetic fields was identified as a factor in this finding. fields were not measured in the

Instead, the researchers devised a method to estimate the magnetic produced by the power lines. The was based on the size and number of line wires and the distance the power lines and the home (p.

A second Denver study in and a 1991 study in Los Angeles, found significant associations living near high-current lines and childhood cancer The L.A. study found an with leukemia but did not look at all The 1988 Denver study an association with all cancer When leukemia was analyzed the risk was elevated but not statistically In neither of these two studies the associations found to be statistically when magnetic fields measured in the home and used in the

Studies in Sweden (1992) and (1993) have found leukemia incidence for children near transmission lines. A Danish study, like the Denver study, found an for incidence of all childhood cancers but not leukemia. A Finnish study an association with central system tumors in boys.

studies have examined of cancer for adults living power lines. Of these, two significant associations with The following chart summarizes from studies involving in people living near lines.

Summary of Residential Cancer Studies

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