Professor Lawrie Challis told the Daily Telegraph children using wi-fi networks should be monitored until research into potential health risks is completed.

He says children should keep a safe distance from the embedded antennas.

The Health Protection Agency has said wi-fi devices are of very low power - much lower than mobile phones.

Prof Challis, retired professor of physics at the University of Nottingham, said: "With a desktop computer, the transmitter will be in the tower.

"This might be perhaps 20cms from your leg and the exposure would then be around one per cent of that from a mobile phone.

"However, if you put a laptop straight on your lap and are using wi-fi, you could be around two centimetres from the transmitter, and receiving comparable exposure to that from a mobile phone."

'Bigger problem'

Prof Challis added that children are much more sensitive than adults to dangers such as pollutants like lead and UV radiation.

"So if there should be a problem with mobiles, then it may be a bigger problem for children.

"Since we advise that children should be discouraged from using mobile phones, we should also discourage children from placing their laptop on their lap when they are using wi-fi.

Meanwhile, teachers have called for an investigation into whether there are any health risks from wireless computer networks in schools.

The Professional Association of Teachers union is writing to the education secretary for a clarification on wi-fi safety.

Many primary and secondary schools use wi-fi networks - but the PAT believes there is insufficient long-term evidence to demonstrate whether such networks are safe.

Students at Canada's Lakehead University have to be careful how they connect to the internet because wi-fi is banned on large parts of the campus.

University president Fred Gilbert, whose academic interests include wildlife management, environmental studies and natural resources science, is worried about the health impact of the 2.4Ghz radio waves used by wireless networks

Last year he decided to adopt the precautionary principle and refused to allow wi-fi in those areas that have what he calls "hard wire connectivity" until it is proved to be safe.

Mr Gilbert believes that "microwave radiation in the frequency range of wi-fi has been shown to increase permeability of the blood-brain barrier, cause behavioural changes, alter cognitive functions, activate a stress response, interfere with brain waves, cell growth, cell communication, calcium ion balance, etc., and cause single and double strand DNA breaks".

Unfortunately the science says he is wrong, and his students are suffering as a result.

Smog talk

While the heating effects of high exposures to electromagnetic radiation can be damaging, the power levels of wireless connections are much lower than the microwave ovens and mobile phones which share the frequency range, and treating them in the same way is the worst sort of scaremongering.

Yet Mr Gilbert is not alone.

And there are a number of pressure groups, campaigning organisations and ill-informed individuals who believe that wireless networks pose a threat to health and want to see them closed down.

Now it seems they have been joined by the editor of the UK newspaper the Independent on Sunday, which this weekend filled its front page with a call for research into the "electronic smog" that is permeating the nation's schools and damaging growing children's' brains.

An accompanying editorial with the even-handed headline "high-tech horrors" called for an official inquiry, while the article outlining the perceived dangers asked "Is the wi-fi revolution a health time bomb?"

The answer, of course, is "no".

That will not stop the newspaper stoking up a wave of opposition to one of the most liberating technologies to have come out of the hi-tech revolution, limiting children's access to networked computers at schools and even blocking plans to develop municipal wireless networks in our towns and cities.

The modulated frequencies that carry Radio 4 and ITV into our homes are just as powerful as the wireless networks, and a lot more pervasive.

And my wireless network is only carrying data when I'm online, while Radio 3 burbles all day long, possibly exciting electrons in my brain and causing headaches.

Then there is the danger from photons of visible light streaming down onto us as we work, since these carry more energy than microwaves and could surely do more damage.

Perhaps we should demand that our children work in the dark.

Test programme

The fuss over wi-fi is the latest manifestation of a general worry about electromagnetic radiation, one whose concerns have ranged over the years from the fields around power transmission lines to the radiation emitted by computer monitors to the microwaves put out by mobile phones.

Campaigners are often supported by those who claim to be so sensitive to electromagnetic radiation that they cannot bear to have a radio turned on in the same room because the fields affect their brains, or those who claim that using a mobile phone gives them headaches.

There is no evidence that electromagnetic radiation at radio frequencies, where the energy levels are too low to dislodge electrons and affect molecular bonding, can cause health effects except by heating tissues.

While those who want to limit the use of wi-fi argue that they need evidence that is it safe, the problem with trying to prove that something is safe is that you can't.

Karl Popper, the great philosopher of science, helped us to understand that science is about falsification, about setting up hypotheses and theories and proving them wrong, because you can never prove them right.

Any theory can be overturned by new evidence, and any claim that wireless networks are completely safe could be thrown out tomorrow if we find good evidence that it isn't.

We may come up with a hitherto unsuspected mechanism that explains a previously disregarded effect, or the evidence may be statistical and require detailed investigation.

Were that to happen we should take it seriously, but it has not happened and there is no reason to believe it will.

The precautionary principle, of avoiding exposure to unnecessary risk, does not apply here because there is no known mechanism by which wireless networks could cause damage.

We have a sound model of the interaction between electromagnetic radiation and organic matter that gives us little reason to believe that there will be any dangers.

For William Stewart, chairman of the Health Protection Agency and a former chief scientific adviser to the Government, to argue for an investigation on the basis of no real evidence that there is an effect, and in the absence of any plausible physical mechanism, is indefensible.

Cellphones heat the brain and could cause problems. Wi-fi doesn't, and it is safe. My daughter is sitting here as I write, her new wireless laptop beside her, and I'm a lot more worried about the damage she would do if she dropped it on her foot than I am about the impact of the low power radio waves it emits.

Bill Thompson is an independent journalist and regular commentator on the BBC World Service programme Digital Planet.

2,http://news.independent.co.uk/uk/health_medical/article2472133.ece

Wi-Fi: Children at risk from 'electronic smog'

::: Revealed - radiation threat from new wireless computer networks
::: Teachers demand inquiry to protect a generation of pupils

By Geoffrey Lean, environment editor

Published: 22 April 2007