Scientists have said there is no evidence to suggest a link between the use of wi-fi and damage to health.

BBC programme Panorama found that radiation levels from wi-fi in one school was up to three times the level of mobile phone mast radiation.

The readings were 600 times below the government's safety limits but there is ongoing debate about wi-fi use.

Sir William Stewart, chairman of the Health Protection Agency, has said there needs to be a review of wi-fi.

He told Panorama that there was evidence that low-level radiation - from devices like mobile phones and wi-fi - did cause adverse health effects.

But some experts in the scientific community have disagreed with his assessment.

"Wi-fi seems unlikely to pose any risk to health," said Professor Lawrie Challis, of Nottingham University.

Prof Challis, chairman of the Mobile Telecommunications and Health Research (MTHR) programme management committee, said: "Wi-fi exposures are usually very small - the transmitters are low power and some distance from the body.

"They can be near to the body, however, when a laptop is on one's lap and my own view is that just as we encourage young children not to use mobile phones we should also encourage them to use their laptops on a table rather than their lap, if they are going online for a long time."

As part of its investigation, Panorama visited a school in Norwich, with more than 1,000 pupils, to compare the level of radiation from a typical mobile phone mast with that of wi-fi in the classroom.

Readings taken for the programme, broadcast on BBC One on Monday, showed the height of wi-fi signal strength to be three times higher in the school classroom than the main beam of radiation intensity from a mobile phone mast.

Greatest intensity

Sir William recommended to the government in 2002 that the beam of greatest intensity from a phone mast should not fall on any part of the school grounds, unless the school and parents agreed to it.

Medical physics expert Professor Malcolm Sperrin told BBC News that the fact wi-fi radiation in a particular school was three times higher than a mobile phone mast was irrelevant, unless there was any evidence of a link to health effects.

"Wi-fi is a technique using very low intensity radio waves. Whilst similar in wavelength to domestic microwave radiation, the intensity of wi-fi radiation is 100,000 times less than that of a domestic microwave oven.

"Furthermore, tissue can only be effectively heated by a wavelength that is closely matched to the absorption, and there are strict guidelines for ensuring such absorption peaks are avoided."

The type of radiation emitted by radio waves (wi-fi), visible light, microwaves and mobile phones has been shown to raise the temperature of tissue at very high levels of exposure - called a thermal interaction - but there is no evidence that low levels cause damage.

The Health Protection Agency has said that sitting in a wi-fi hotspot for a year results in receiving the same dose of radio waves as making a 20-minute mobile phone call.

"Some people suspect a non-thermal interaction but there is no evidence to suggest that this exists and indeed it is unlikely," said Prof Sperrin.

Research proceeding

He added: "Radio waves (wi-fi) and other non-ionising radiations have been part of our lives for a century or more and if such effects were occurring then damage or other untoward effects would have been recorded and studied.

Research is still proceeding in this area at leading centres in many countries but evidence points to wi-fi transmissions being well below any likely threshold for human effects."

Panorama spoke to Professor Olle Johansson, of the Karolinska Institute in Sweden, who said there had been many recorded effects such as chromosome damage from low-level radiation.

Professor Henry Lai, from Washington state university, also quoted in Panorama, said he had found health effects at similar levels of radiation to wi-fi.

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