electromagnetic waves such as radio waves and light waves have an electrical wave and a magnetic wave at right angles to it and thus sources can give off both an electric field and a magnetic field
electric and magnetic fields occur naturally and also come from human-made sources and are made whenever electricity is used
this page is for EMF associated with extremely low-frequency (ELF) radiation from power supplies, etc and radio frequency EMF, it does not include light, UV, X-rays or gamma rays (see Ionising radiation for the latter two
at usual exposures, the evidence would suggest they do little harm, nevertheless, many advocate for minimal exposure targets where possible, especially where children live such as in houses, schools and playgrounds as there have been suggestions prolonged exposures to magnetic fields higher than 0.4µT may double the risk of childhood leukaemia
health concerns are for two quite separate non-ionising frequency bands:
50/60Hz AC currents which produce ELF
0.4-5GHz radio wave frequencies such as WiFi, mobile phones
Australia has strict controls on the use of radio equipment as well as power equipment and power supply lines aimed to minimise adverse effects
eg. unlicensed users are restricted to 5W CB 2-way radios, while foundation licensed users can use up to 10W, unlicensed users are NOT permitted to transmitted on any other bands (apart from usual devices such as WiFi Routers, mobile phones, Bluetooth, low energy approved devices), and only those with ham radio licenses can transmit on the amateur radio bands
eg. all devices capable of transmitting radio must be approved and certified
Measuring EMF
electromagnetic wave intensity in air is usually given as W/m2
all electromagnetic waves including radio waves and light obey the inverse square rule whereby the intensity falls to a quarter each time the distance from the source is doubled
electric fields are usually given as V/m or kV/m
magnetic fields are usually given as µT, mG (1mG = 0.1µT) or A/m (1 A/m = 0.5µT)
Specific Absorption Rate (SAR) by the body are usually given as W/kg
General advised maximum target levels of exposure
occupational for workers using electrical equipment: 10kV/m and for magnetic fields, 500 µT
exposure to frequencies between 10 MHz and 10 GHz, the limit for average power absorbed by the whole body is 0.4 W/kg, while the maximum SAR for the head and torso is 10 W/kg and the maximum SAR for the limbs is 20 W/kg 1)
at a frequency of 900 MHz, field levels of up to 4.5 W/m² satisfy this requirement, while at 1.8 GHz, field levels of up to 9.0 W/m² fall within the limit2)
general public (eg. power transmission lines): 5kV/m and for magnetic fields is 200 µT or 2000 mG
exposure to frequencies between 10 MHz and 10 GHz, the average power absorbed by the whole body should not exceed an SAR of 0.08 W/kg. The maximum SAR for the head and torso is 2.0 W/kg, while for the limbs it is 4.0 W/kg. 3)
houses, schools and playgrounds: 10V/m and magnetic fields below 0.05µT
an individual’s highest exposure is typically from any mobile device used in close proximity to the body and typically produce maximum absorbed powers (SAR) in the area of the body they touch, for example the head or limbs.
Example fields
most houses have background magnetic fields of 0.01-0.2µT however, this can be much higher if very close to high output mains sources can reach 1000 µT and 200V/m
a charging smartphone can produce 1kV/m within a cm but this rapidly dissipates to low levels by 30cm
high-voltage overhead power lines - up to 10 kV/m and 100 µT
small cell 5G mobile phone base stations produce weaker fields than 3G and 4G masts
IoT devices will usually produce weaker EMFs than other appliances and systems, because they only transmit information periodically and in small amounts
WLAN routers have very low power signals, typically 0.1 W
potential very high exposures:
faulty microwave ovens
commercial radio transmission towers
touching a tower whilst it is on and you are grounded can cause very severe burns
usually have fences to warn people but youth may not heed this
even if turned off, they can cause a large static electric shock from nearby transmitters which may cause someone climbing it to fall
intense RF fields used in medical Rx may cause issues
intense beams of 60GHz radiofrequency which cause heating and pain have been developed as a means of crowd control by the military
Clinical effects
50/60Hz AC power frequency extremely low-frequency (ELF) radiation fields
at 10–100 mV/m, low-frequency (20 Hz) electric and magnetic fields are able to interact with synapses in the retina to cause a flickering light sensation called electrophosphenes or magnetophophenes respectively
above 6 V/m it causes small currents to flow in the peripheral nervous system
above 10 V/m it causes small currents to flow in the central nervous system
cardiac tissue is excitable at relatively high exposure levels (12.0 V/m peak)
above 2 kV/m to 5 kV/m it can also cause non-lethal static electricity micro-shocks when a metal object is touched - much as walking across nylon carpet does
burns may occur with very high levels of exposure
myelinated nerves are thicker and more sensitive to EMF than unmyelinated nerves as in the grey matter of the CNS4)
people with epilepsy may be more sensitive to 50/60Hz EMF than others
long term exposures to magnetic fields above 0.3-0.4µT have been associated with a doubling of the risk of childhood leukaemia although the evidence is limited and causation seems unlikely
Higher frequency radio wave fields
medical implants such as orthopaedic rods as well as some costume jewellery may act as an antenna to concentrate an RF field esp. at < 100kHz
high levels of electromagnetic interference of medical devices can be an issue eg. cardiac pacemakers, implantable defibrillators
high levels can induce currents in the body, although nerve stimulation is unlikely at frequencies above 10 MHz
at higher frequencies, EMFs can generate heat in the body, causing body temperature to rise
exposure to fields that generate temperature rises of more than 1-2 ºC can overwhelm the body’s thermoregulatory capacity and can cause tissue damage
hence the limit of whole-body exposure to a maximum SAR of 0.08 W/kg
for perspective though this heating is similar to that caused by moderate exercise such as a brisk walk or taking a warm bath
as frequency increases, EMF exposure of the body and the resultant heating becomes more superficial
above 6GHz, exposure is mainly on the skin and the heat is more easily dispersed into the environment
much debate as been had on the potential adverse effects of mobile phones frequently held near the head to cause intracranial tumours however there is no sound evidence to support this 5)
there is no good evidence to implicate neurobehavioural adverse effects at usual exposures
very high levels sufficient to cause local heating effects may cause:
heating of muscles and potential for compartment syndrome
burns
keratitis and iritis
thermally hazardous levels may cause slow onset cataracts taking weeks after a high exposure event
headaches, lethargy and cognitive effects such as decreased concentration
prolonged dysasthesiae / paraesthesiae
delayed, persistent hypertension via autonomic system exposure
transient male infertility due to over-heating of testes
potential adverse fetal effects including risk of miscarriage (MHz frequencies in early pregnancy, GHz in later pregnancy)
despite the absence of good evidence for mobile phones to adversely effect health due to EMF, it is prudent not to have it near your head on charge while you are sleeping
electric field is much higher when it is on charge (can be 500-1000V/m 1cm away) and you are within 15-30cm
lithium ion battery explosions can occur, usually when charging overnight and you don't want to be near it if this happens!