Wi-Fi Is It Damaging Childrens Health

[CliffyG]

I'm of the opinion that this is sensationalisim although do agree that wireless in schools is a little pointless. Here some info one of the science bods at my work emailed earlier, a pretty interesting read.

A WLAN device only ever transmits a total power of a tenth of a watt - that's about the same as the power that sunlight delivers to a 1 cm square of your skin in summer.

Only a small proportion of the WLAN emissions reach a persons body since the device transmits in all directions at once in order to function. For example if a person is standing 5 meters away, and assuming a person's frontal surface area is about 1m square, they may receive about 1/300th of the total output power. That's about 0.3 mW over the whole body. If they stand 10m away this drops by a factor of 4. In addition, the WLAN terminal typically only transmits when files are actively being moved which tends to be a very small proportion of the time. Finally, much of the energy that is incident on the body will actually reflect from or pass through without being absorbed.

Obviously this discussion applies to the stated concern of children being in areas where WLAN systems are in operation. If they are using a WLAN enabled system themselves, the levels are higher, but the basic argument still applies... Lower power than a phone, emitted only during data transfer, and emitted from a point many times further away from the head than a mobile would be held.

To compare, A GSM base station can transmit up to 20W of power, although smaller basestations, and the phones themselves transmit around 1W. Power control is used so that the mobile and the basestation try to use just enough power for the job. This is the basis for the argument that exposure is actually reduced by placing a base site on the roof of a school or hospital. However the reality is that at medium or long range (or even when using a phone indoors) both the phone and the base site will turn the power up. It is a technicality to say that a WLAN terminal can transmit more power than a cellular base site. This is not the case for the majority of the time.

To make the comparison between levels still more clearly, the WLAN devices are designed to operate down to a pico Watt. That's a millionth of a millionth of a watt. (Apologies to all techies). Ie, in reality, the power received from a WLAN access point in the corner of a classroom by the people in it will typically be between a millionth and a billionth of a watt... When it is operating... and that's over the whole body. Compared to a tenth of a watt over every cm of skin, every second that a person is exposed to sunlight.

It is true that different frequencies of electromagnetic radiation have different effects. X Rays for example, much higher in frequency and energy than visible radiation, do more damage to biology. This is why X Rays are considered dangerous even in low doses. Visible light as we all know can be slightly dangerous in large doses and is known to be harmful over long time frames. Microwave radiation is much lower again in frequency. Its effects are thermal rather than ionizing. ie - it will warm you up rather than smash your molecules.

It is also true that the full effects of long term exposure haven't been very well studied and therefore are poorly known. However the amount of power in a WLAN signal is very very low. If you use a Mobile phone for an hour this is a much higher dose - perhaps 1000 times as high - as the energy received from either a cellular base station on the roof of a school, or a WLAN terminal used heavily all day. Which is itself maybe a thousand times higher than simply being in a classroom with an access point. In fact it may be the case that TV broadcast signals expose many of us to more electromagnetic energy than the WLAN device on the wall.