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Electromagnetic «Smog »? The rapid growth and proliferation of wireless telecommunication systems, cellular telephony chief among them, has contributed to an equally rapid increase in the levels of RF radiation in our environment. Numerous questions exist regarding the health effects of RF radiation: Is RF radiation dangerous? What level of RF radiation can be considered as safe? What methods of protection against excessive levels of RF radiation can be used? Safety Code 6 Radiation Protection Bureau of Health Canada publishes "Limits of Human Exposure to Radiofrequency Electromagnetic Fields in the Frequency Range from 3 kHz to 300 GHz". These limits are based on a review of scientific work conducted over the last thirty years and are set at levels 10 times lower than the thresholds where potentially harmful effects begin. At YRH, we've been concerned for more than 10 years already, with the recommendations of that document, more commonly known as "Safety Code 6". The exposure limits recommended by the Safety Code 6 are specified in terms of intensity of electromagnetic fields and different limit values are specified for people exposed in the course of their work (occupational exposure) and for the general public. Safety Code 6 therefore also specifies limit values for induced body currents as well as contact currents. At lower frequencies, such as the FM band, electromagnetic fields can induce electric currents in the human body an in other conducting objects. Compliance assessment The evaluation of RF radiation levels in a given situation is necessary to determine if the RF levels respect the recommendations of Safety Code 6, either for the protection of the general public or for safe working conditions for RF workers. RF field levels can be modelled theoretically, which allows to assess the RF field levels of existing installations as well as of future situations. Moreover, a theoretical assessment can evaluate RF field levels even for locations that are not easily accessible. Whenever possible, on-site measurements
should be performed to supplement the theoretical results. The type
of measurements that need to be performed on a given site depends
on the frequencies used at this site and different types of survey
equipment can be selected accordingly. |
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Exposure limits (Click on the picture to enlarge) Maximum exposure values specified by Safety Code 6 vary with the frequency. In a multiple frequency environment this fact must be taken into account: the RF field level generated at each frequency must be compared to the maximum exposure value specified for this frequency in order to evaluate the total effect.
Theoretical Assessment
Green and yellow sections of the roof can be accessed by workers for unlimited time periods without any reduction of transmitter power. Red sections should not be accessed except under specific circumstances.
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On-Site Measurement of RF Levels The elements of a measurement session and the types of equipment used will depend of the site configuration and on the frequencies present at that site: AM, Fm, TV, mobile communications, cellular telephony, PCS , etc… In most situations, the intensity of electromagnetic fields can be measured using a broadband electric field probe with shaped frequency response so that readings can be taken directly in as a percentage of Safety Code 6 limit. In other situations, such as measurements on AM sites, it will be necessary to measure both the electric and the magnetic field in dependently. On sites where FM and TV antennas are located it is also necessary to measure currents induced in the body. YRH measurement team uses a ferrite-core induced current meter similar to a commonly used clamp-on current meter. This device is worn around the ankle and measures the current flowing through it. Living and Working in a RF World In order to establish a tailor-made safety program for a specific site, the first step is to compile results from a theoretical analysis and on-site measurements. The first step in ensuring site compliance is to lower RF field levels below Safety Code 6 recommendations in all areas that can normally be accessed by the general public. Different methods are available for lowering RF levels. If areas exceeding Safety Code 6 recommendations remain, should be clearly identified with appropriate warning signs and general public access to these areas should be restricted. The distribution of RF field levels on a site and safe work procedures in all areas of the site should be available at the site so that all work will be done in a safe environment with regards to FR field intensities. If areas of high field intensities and the levels present in those areas are identified, a worker will be able to determine the amount of time he can spend in a given area or if he is required to wear a RF protection suit. Personal monitors are another piece of equipment that will alert the worker to the presence of high-intensity RF fields. RF levels at a site should be periodically re-evaluated as well as after each change to the site, weather it is directly related to RF equipment or not. For example, the installation of a new ventilation equipment on a roof-top site can have significant impact on the distribution of RF levels. Our expertise in
RF evaluation
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RF Measurements
Using a Broadband Field Probe
Induced Current Meter
Warning Signs Designed
by YRH
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