All form of Electromagnetic energy when taken together form the electromagnetic spectrum.The frequency of the electromagnetic energy is important in determining how it will interact with the biological system.
Gamma rays,X-rays, and the higher ultraviolet part of the electromagnetic spectrum are ionizing, where as the lower part of the spectrum, including visible light, infrared, microwaves and radio waves are all considered non-ionizing radiation. The boundary between ionizing and non-ionizing electromagnetic radiation that occurs in the ultraviolet is not sharply defined.
Ionizing radiation is radiation with enough energy so that during an interaction with an atom, it can remove tightly bound electrons from the orbit of an atom, causing the atom to become charged or ionized.It is the energy or particles (protons, electrons or neutrons) produced by unstable atoms of radioactive materials. It is present in the environment, as a result of both naturally occurring radioactive minerals and cosmic radiation arriving from outer space. Ionizing radiation is also produced by certain human activities, such as medicine and industry, and may result from accidents in nuclear facilities and nuclear bomb explosions.When absorbed by the body, radiation produces toxic free radicals. Exposure to high levels of radiation can cause substantial damage to human body tissues, and may lead to death. Prolonged exposure to lower levels is also associated with increased risk of ill-health.
Non-ionizing radiation, the other hand, is the term given to radiation in the part of the electromagnetic spectrum where there is insufficient energy to cause ionization. It includes electric and magnetic fields, radio waves, microwaves, infrared, ultraviolet, and visible radiation.
To summarize,
Radio frequency (RF) signals are electromagnetic energy. Electromagnetic energy comes from natural sources like the sun as well as man made sources.
RF is non-ionizing, unlike x-rays. It has insufficient intrinsic (quantum) energy damage.
Excessive exposure to RF signals causes heating of the body. There are standards in place to provide protection to workers and the public and the measure of the amount of absorption is SAR(Specific Absorption Rate) measured in W/kg.
It is important to distinguish biological effects and health hazards.Effect is a response within normal range while hazard is a response outside normal range.
Studies show that:
Established effects form the basis of RF exposure standards
IARC - INTERNATIONAL AGENCY for RESEARCH on CANCER
- the only adverse effects that have been clearly observed and understood are the acute(immediate)
- Absorption of RF energy leads to an increase of body temperature
- Thermal effects exhibits threshols that are well above levels that are experienced by the public
- Exposure limits (well below thresholds) totally prevents such effects
IARC - INTERNATIONAL AGENCY for RESEARCH on CANCER
- part of the World Health Organization
- Its MISSION : cancer research for cancer prevention
HUMAN EXPOSURE LIMITS
INTERNATIONAL LIMITS FOR WORKERS AND THE PUBLIC
The EMF exposure mechanism was developed by ICNIRP (International Commission on Non-Ionizing Radiation Protection)
The EMF exposure mechanism was developed by ICNIRP (International Commission on Non-Ionizing Radiation Protection)
Whole body heating
Formula for SAR
(unit of W/kg)
Where: σ = dielectric conductivity (Siemens/m – S/m)
ρ = tissue density (kg/m3);
E = internal rms electric field strength (V/m)
It can also be calculated from the rate of temperature rise.
FACTORS AFFECTING THE WHOLE BODY SAR
- core body temperature varies naturally about 1ºC
- Core body temperature rises of more than 1-2 ºC over prolonged periods can have adverse health effects such as heat exhaustion (headache, nausea & dizziness) and heat stroke• SAR = specific absorption rate (units of W/kg)
- The rate at which RF energy is absorbed in body tissues • Normal loads from activity vary from about 1 to 10 W/kg
- A whole-body-average SAR of 1 W/kg for one hour, and up to 4 W/kg for short periods, will result in a rise of less than 1ºC in core body temperature in resting subjects in moderate thermal environments
Formula for SAR
(unit of W/kg)
Where: σ = dielectric conductivity (Siemens/m – S/m)
ρ = tissue density (kg/m3);
E = internal rms electric field strength (V/m)
It can also be calculated from the rate of temperature rise.
FACTORS AFFECTING THE WHOLE BODY SAR
- Intensity of the RF field
- Frequency of the RF field
- Polarization of the RF field
- Size of the person
- Grounding of the person
WHO and ITU recommend ICNIRP limits
GENERAL PRINCIPLES for RF exposure evaluations
- Identify appropriate compliance limits
- determine if RF exposure assessment is needed, If need, RF exposure assessment is done by calculations and measurement.
- If exposure limits may be exceeded, apply mitigation
COMPLIANCE
Examples in determining if multiple sources in a site are compliant
Since exposure reduces rapidly with increase distance, the public shall not enter the compliance boundary of sites.
Summary from WHO
ARD