"Are phone masts cancerous?" is the headline on one of today's letters (March 29).

Any electro-magnetic (EM) radiation is potentially harmful.

As a CB-radio user in the Eighties, it was not unknown to get an occasional burn from holding the aerial while transmitting at 4 watts.

But, then, you don't hold mobile phone aerials. So, how far away from them is safe?

A typical phone mast broadcasts in the tens of watts, so let's say it is transmitting at 100 watts as a worst case, which is measured at one metre from the mast.

The inverse square law applies here, so, at ten times the distance, you'll only get a hundredth of the power.

So, roughly speaking, at the bottom of the 20m pole on which the aerial stands, you'll receive about half a watt of power or, roughly speaking, about the same power as you receive from a mobile phone held to the side of your head.

Compare this with standing at the bottom of a mast transmitting TV signals. The Whitehawk transmitter broadcasts at 2,000 watts.

Assumming it is also about 20m high, at the bottom you would receive about five watts.

So, 20m from the worst phone mast transmitter should give you the same power through you as your own mobile phone.

Another 20m away and the power received from the pole is only a four-hundredth of what you receive from your mobile phone.

You get more EM radiation from watching your TV.

-Rod Main, Newhaven