What is wi-fi?

Wi-fi is a technology which enables devices to communicate with one another using radio frequency.

How strong is it?

The signal emitted by a wi-fi device is about 100 milliwatts – slightly weaker than a mobile phone, at 125 milliwatts. (A lightbulb, which also emits electro-magnetic radiation, is stronger than both, at 60 or 100 watts.) The freqeuncy is approximately 2,300 to 2,400 megahertz, which is comparable to that of 3G mobile phones – about 2,100 megahertz.

Is wi-fi safe?

So far, there's been relatively little research into the potential health effects of wi-fi in comparison with mobile phones. Scientists in Sweden have expressed concern about a range of potential side effects of exposure from chromosome damage to short term memory loss, but the advice from the World Health Organisation remains that there is "no adverse health effects from low level, long-term exposure". The British Government's position is that wi-fi devices "are of very low power, much lower than mobile phones."

Why hasn't more research been done?

Part of the difficulty of investigating the potential health effects of wi-fi is that people's exposure to it varies greatly. The fact that mobile phones are universally pressed to users' heads meant that scientists could begin with the hypothesis that there was a link between phones and brain cancer. (A study of 2,782 people across the UK associated with the international project Interphone found last year that there was no link between the risk of developing a brain tumour and length of phone use.)

With wi-fi, the potential effect is less clear. "Which condition do you investigate the link with?" one Government health source said. "Testicular cancer? Because computers rest on people's laps? Epilepsy?"

Also, the location of the wi-fi chip in computers is changing. A wi-fi connection used to be established by inserting a card in the base of the computer – meaning the signal would transmit closer to the body – but increasingly the chip is in the screen at the back, meaning it is further away from a user's lap (in the case of a laptop). "With radiation and its effects, proximity is all," the health source said.

How do wi-fi 'clouds' compare with mobile phone masts?

In 2000 the Government recommended that a precautionary approach be taken when siting mobile phone masts near schools followed an inquiry into the relationship between such masts and health. "We recommended, because we were sensitive about children... that masts should not necessarily impact directly on areas where children were exposed, like playgrounds and that," Sir William Stewart, who is now chairman of the Health Protection Agency (HPA), told the BBC.

The Panorama investigation claims to have found that the level of radiation in a wirelesly networked classroom in Norwich was three times that emitted from a mobile phone mast.

But even then, the reading was up to 600 times below the Government's recommended safety level for exposure.

"You're talking about a thousand times less than the level to which kids are exposed when they hold a phone to their head," a source close to the HPA said. "There's no way a wireless router at the edge of a classroom can give you as much exposure as talking on a mobile phone."

In addition, a wireless connection between a router and a computer is only activated when the user requests a communication, meaning that the overall level to which a student using a computer is exposed would be less than if the connection were constant.

Will the research now take place?

The HPA has said it would like to see a study into the levels of expoure to wi-fi in schools, but that such research would not be "trivial" and would cost in the hundreds of thousands of pounds. It would need to be approved by schools and local authorities and receive significant funding, probably from the Department of Health. A DoH spokesman was not available for comment.

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