Measuring Magnetic Fields

Transmission lines and distribution lines generate a magnetic field. What intensity does the magnetic field have?
The intensity is up to approximately 20 μT at one meter above the ground directly beneath transmission and distribution lines.*

* Source: Fiscal 2003 Survey Report, Environmental Impact Survey of Power Facilities (Nuclear and Industrial Safety Agency, Ministry of Economy, Trade and Industry)
What is the intensity of the magnetic field of a substation?
The intensity is up to 4 μT or so on the border between the premises of the substation and neighbouring ordinary land.*

* Source: Fiscal 2003 Survey Report, Environmental Impact Survey of Power Facilities (Nuclear and Industrial Safety Agency, Ministry of Economy, Trade and Industry)
How does the intensity of a magnetic field change in respect to the distance from transmission lines?
The intensity of a magnetic field decreases rapidly as the distance from the source increases. For example, suppose that the intensity of a magnetic field directly beneath the center of transmission lines is approximately 4.4 μT. When the distance from the center is 20 m, the intensity becomes approximately 2.2 μT; at 40 m, 0.6 μT; 60 m, 0.1 μT; 80 m, 0.05 μT; and 100 m, 0.02 μT. However, these values may change depending on the facility.*

* Source: Fiscal 2003 Survey Report, Environmental Impact Survey of Power Facilities (Nuclear and Industrial Safety Agency, Ministry of Economy, Trade and Industry)
What intensity does the magnetic field of home electric appliances have?
A fiscal 2004 report** prepared by the Ministry of the Environment describes results from measuring the intensities of magnetic fields generated from home electric appliances. Based on the report, magnetic field levels of major home electric appliances are listed below. Before studying these measurement results, be sure to check the following points:

【Points to note】
☆ Some home electric appliances that use 50 or 60 Hz alternative current generate the magnetic field of a frequency band that differs from the power supply frequency. They include home electric appliances such as IH stoves, apparatuses that use motors, and cathode-ray tube TVs. The numeric values reported as the magnetic field intensities of these appliances cannot be compared directly with those of 50 and 60 Hz home electric appliances and with the limit values specified in the protection guidelines. The intensity varies, depending on the measurement instrument used and the measurement conditions.

☆ When magnetic field distribution is uneven, the intensity varies depending on the measurement point. The intensity also depends on the space resolution of the measurement instrument. In general, the level of the magnetic field near the appliances is larger, becoming smaller with distance increasing. After considering the positional relationship between the human body and the appliance generating EMF under the actual use environment, you need to decide which measurement point is appropriate for adopting the intensity of the magnetic field as the strength index. For example, the intensity may be measured on the top burner of an IH stove. That point is unrealistic for measuring the intensity because the human body does not stay at that measurement point when using the IH stove.

☆ When you compare the magnetic field intensity of an appliance with the reference value specified in the guidelines of the International Commission on Non-Ionizing Radiation Protection (ICNIRP), you must understand that the reference values in the ICNIRP guidelines are meaningful only when the entire human body is exposed to EMF. When only part of the body is exposed to EMF near the appliance and even when the magnetic field intensity is above the reference value specified in the ICNIRP guidelines, it does not mean that the magnetic field intensity exceeds the value in the protection guidelines.

Comparison of Ionizing and Nonionizing Radiation as Particle Energy

* Source: Fiscal 2004 Survey Report on Electromagnetic Fields in Living Environments (Ministry of the Environment)

→Reference documents:
Fiscal 2004 Survey Report on Electromagnetic Fields in Living Environments (Ministry of the Environment)

→IEC standard:
☆Measurement distances based on international standard IEC 62233 with regard to the method for measuring home electric appliances
Is EMF measurable?
Yes, EMF can be measured with existing instruments. However, to evaluate the effects of EMF correctly, you need to consider the distance between the EMF source and the measurement point, power supply frequency, measurement instrument and calibration, range and allowance of the measurement instrument, and other factors.
What organizations offer EMF measurement services?
For EMF generating from power facilities, regional electric power companies conduct EMF measurement. For more information, refer to the website of the electric power company in your area.
Does the Japan EMF Information Center (JEIC) offer EMF measurement services?
JEIC is now unable to offer measurement services due to limited personnel, but is going to study a method to use instead of measuring EMF. In connection with this, the JEIC only measures ELF EMF. JEIC has no plans to measure other frequencies or lend measurement instruments.
What is the level of electromagnetic waves (electric waves) emitted from cellular phones and cellular phone base stations?
As a cellular phone is used near the side of human head, the evaluation is made based on local SAR (Specific Absorption Rate). You can find the value of local SAR for each model type of cellular phones on the website of telecommunications carriers.

The level of electromagnetic waves (electric waves) emitted from cellular phone base stations tends to be higher at the point several hundred meters away than at the point close to the station, as directionality is given to the antenna. In any cases, the level is much lower than the standard.
When I measured the magnetic fields of an IH cooking device, a very high value was shown for the surface where pans and pots contact. Is that all right?
It is physically possible to reduce magnetic fields by covering the device or the space you want to reduce the magnetic fields with shielding objects using special material. However, such measures are extremely costly.

WHO Fact Sheet No. 205 “Extremely Low Frequency (ELF)” and the explanation on the background “Caution Measures” state that “The closer to the device, the stronger the electric fields and magnetic fields are and they diminish with distance. Common materials, such as wood and metal, shield against electric fields. Magnetic fields are not shielded by most common materials, and pass easily through them.” It is possible to reduce electric fields with common materials, but it is very difficult to reduce magnetic fields. Possible measures to easily reduce magnetic fields include: keeping electric devices and other devices that emit electromagnetic fields away from bed; moving children’s beds to the place in the room where magnetic fields are weak; warming up an electric blanket beforehand and turn off power just before going to bed. WHO Fact Sheet No.322 “Exposure to extremely low frequency fields” and the Ministry of Economy, Trade and Industry “Report of working group for countermeasures against electric facilities electromagnetic fields” suggest that we had better seek for low-cost measures to reduce magnetic fields if we do, because benefits of reducing magnetic fields for our health are uncertain.
I would like to know measuring principles and types of low-frequency magnetic fields measuring devices.
A Magnetic field measuring device has a coil inside it and measures the levels of voltage induced at the both ends of the coil corresponding to a change in magnetic fields. There are two types of measuring devices: single-axis type and three-axis type. Three-axis type has coils in three directions, i.e. x-axis, y-axis and z-axis, each, and some devices show a combined value of the three. You need to choose a measuring device that is suitable for frequency of electromagnetic fields to be measured.
Are there any standard methods to measure electromagnetic fields?
International Electrotechnical Commission (IEC) has set the standards that specify measurement methods of electric and magnetic fields generated from electric facilities, including transmission lines and substations, and home electric appliances. IEC also has the standards for electric facilities: IEC 62110 Electric and magnetic field levels generated by AC power systems and IEC 62233 Measurement methods for electromagnetic fields of household appliances and similar apparatus with regard to human exposure.

As the methods to confirm a compliance with the standards of the enforcement regulations of the Radio Act for high-frequency electromagnetic waves (electric waves), “Calculation and measurement methods for the strength of electric waves emitted from radio equipment” (the Public Notice No.300 of the Posts and Telecommunications Ministry) was released. There is also the “Handbook for confirmation of compliance with the standards for protection against electric waves” (the Ministry of Internal Affairs and Communications) that describes the outline of the calculation and measurement methods for the strength of electric waves specified in the Public Notice.
How strong are the magnetic fields generated by linear motor cars (maglev trains) ?
The electromagnetic fields generated by linear motor cars (maglev trains) are mainly static magnetic fields. The limit for static magnetic fields specified by international guidelines is 2 tesla (T). We believe that trains must be designed assuming various passengers. We expect that sufficient countermeasures will have been taken when it starts operation.

The measurement result of magnetic fields generated by linear motor cars is as shown below. (Insert a chart)
Do the electromagnetic fields around railway tracks exist only when Shinkansen is passing?
Since Shinkansen runs receiving AC current electricity, the magnetic fields similar to those of transmission lines is considered to occur around the train.

Also, as Shinkansen is supplied with electricity in certain sections, the magnetic fields may occur in some cases when Shinkansen is running through such a section even if it does not pass before your eyes.
Once I turn off the cellular phone, don’t electromagnetic waves (electric waves) occur at all?
When the cellular phone is turned off, electromagnetic waves do not occur. Electromagnetic waves occur while you start calling and you are talking on the phone. Even when the power is turned on and you do not use it, electric waves are emitted automatically from your cellular phone when the area of your cellular phone base station changes during moving on a train. (*) This is to register the cellular phone in the base stations that covers the relevant area.

(*) Even when the area of cellular phone base station does not change, the cellular phone emits electric waves, as the base station and the cellular phone transmit and receive electric waves each other at all times to check the location of the cellular phone.
Are electromagnetic fields generated by antenna wire (feeder wire) of TV set?
A signal of airwave of television broadcasts runs through antenna wire (feeder wire). Although, electromagnetic fields occur around it, its strength is very weak, as this signal is weak electric current.
Why magnetic fields of a hair dryer are larger than other home electric appliances?
It is because the distance between a hair dryer and the human body is short when it is used and it uses much power and has big electric current. A dryer has a blast motor with coiled structure inside. The strength of magnetic fields generated from the coiled part is the multiple of the base strength by the number of turns of coil. Therefore, home electric appliances with motor generate larger magnetic fields in general.
The strength of magnetic fields generated from electric facilities such as transmission lines and distribution lines is said to be at the same level as that of home electric appliances. However, I think they should be considered differently because hour of use is different.
As you pointed out, there is a difference in duration of time during which magnetic fields occur between home electric appliances and electric facilities. We use home electric appliances for a short period of time, while electricity flows in electric facilities at all times. However, magnetic fields are not accumulated in your body. A causal relationship with human health has not been verified, either. Therefore, we cannot answer whether we can consider them in the same way or not. In epidemiological studies, the average of magnetic fields that are measured for 24 hours to 1 week is used as an indicator. This average value includes magnetic fields generated from both home electric appliances and electric facilities.