Monday 31 August, 2015, 14:13 - Spectrum ManagementA number of people claim that they have had adverse medical and psychological responses to the presence of WiFi signals. But can WiFi actually constitute a health hazard? Wireless Waffle investigates...
Posted by Administrator
Posted by Administrator
Let's begin by considering the international rules which establish the limits for which exposure to radio signals is deemed to be detrimental to health as defined by the International Commission on Non-Ionising Radiation Protection (ICNIRP for short). ICNIRP has established a set of limits for the general public which are designed to stop the temperature of an average human body rising by more than 1 degree Centigrade over a roughly 24 hour period. This level of exposure is 50 times below that at which any measurable biological effects on humans have been identified.
These limits, measured in terms of the measured electrical field strength in Volts per metre, are shown below over a range of different frequencies.
But what do they mean in practice and how does this help calculate whether WiFi could be dangerous. A WiFi transmitter, operating at full power (100 milliWatts, or 0.1 Watts) that is 2 metres (or 6 feet) away, produces an electrical field strength of just over 1 Volt per metre. The threshold of danger at the frequency that WiFi operates - 2450 MHz - is 61 Volts per metre and so at just 2 metres distant, the signal from a WiFi device is 61 times below the safety limit.
There is another, and maybe more straightforward, way to calculate whether or not a radio transmission is likely to be dangerous. According to the laws of physics (which as everyone knows, canna be changed) 1 Watt of power (equivalent to 1 Joule per second) will raise the temperature of 1 gram (or 1 ml) of water by 1 degree Centigrade in 1 second assuming that all of the power can be focussed into the water. This is effectively how microwave ovens work: radio energy is focussed into the water in whatever is being cooked, heating it up.
If, for the sake of argument, we make the assumption that an 'average' human being weighs 50 kg (110 lb), and that it is made largely of water, it would take 50,000 Watts (or 50 kW) of energy to raise their temperature by 1 degree Centigrade in 1 second. To do the same job over the 24 hour period defined by ICNIRP would require 86,400 times less (60 x 60 x 24) meaning that if our average human absorbed around 0.6 Watts of energy for a 24 hour period, this would be deemed to be unsafe. WiFi transmitters have a maximum transmitter power (limited by law) of 0.1 Watts, which is below this limit. So even if ALL of the power transmitted by a WiFi device were absorbed by a human for 24 hours, it would still be a factor of 6 times lower than the ICNIRP safety limit.
In reality, it would be impossible to absorb all of the power from a WiFi transmitter unless that transmitter was inside the human body. Even if the antenna was placed directly on the skin, as signals from a WiFi transmitter are sent out equally in all directions at least half of the power would radiate away from the body, further reducing the impact on the human concerned.
If the WiFi transmitter is 2 metres away, the signal from the WiFi antenna will have spread out so much that far less than a tenth of the original signal would wash over the body of a human, putting the exposure at a factor 60 times below the ICNIRP limit - gratifyingly the same as the level of exposure calculated using the graph above.
It is also worth noting that WiFi transmitters do not transmit constantly. At their busiest, they transmit around 50% of the time (they spend the other 50% of the time listening for incoming transmissions). Any exposure will therefore be another factor of 2 times smaller than above.
So what is the conclusion? As long as you don't swallow 6 transmitting WiFi antennas that continue to transmit on full power for a 24 hour period, any radiation from WiFi transmitters is far, far (far) below the established safety limits.