The government has ordered a wide-ranging investigation into wireless computer networks amid concerns over the potential health risks they pose for millions of schoolchildren and office workers.

The Health Protection Agency (HPA) will spend two years conducting lab tests and monitoring exposure levels to the wireless signals in classrooms, homes and offices, before compiling a health risk report on the technology.

Fears over the potential risks of wireless networks have led some school governors to order their withdrawal from classrooms.

Last month, Philip Parkin, the general secretary of the Professional Association of Teachers, said usage of the networks should be suspended in schools until a full inquiry into the health effects had been conducted. Health agency officials said there was no scientific evidence to suggest the networks pose a danger to health, and expected the studies to record exposure levels "thousands of times below guideline safety limits".

Pat Troop, chief executive of the HPA, said that while there was no health reason for schools and others to discontinue use of wireless networks, "there has not been extensive research into what people's exposures are to this new technology, and that is why we are initiating this new programme of research and analysis".

The investigation will begin with computer models and laboratory simulations to measure the strength of the signals emitted by computers and their wireless base stations. Dummies fitted with microwave radiation monitors will be used to record exposures at the head level and in other parts of the body.

The investigation will then shift to homes, offices and schools. Officials are particularly keen to measure exposure levels in classrooms, where tens of computers may be hooked up to a wireless network at the same time.

Safety guidelines drawn up by the International Commission on Non-Ionising Radiation set an exposure limit of two watts a kilo for the head. Previous measurements of the signals suggest power levels are typically 20 times weaker than that at 0.1 watts a kilo.

Michael Clark, science spokesman for the HPA, said: "Like mobile phone usage, Wi-Fi has undergone a rapid expansion and we feel there should be a proper scientific database on what the actual exposure levels are, so we can have a proper debate about it."

Mr Parkin welcomed the investigation but said the HPA must also look into so-called "non-thermal effects" of the wireless signals. Safety guidelines are set to ensure signals are too weak to heat up body tissues, but some researchers fear the waves may cause damage to cells in other ways.

"If they don't do a thorough investigation, people will see it as a whitewash," Mr Parkin said. "What we want is a thorough investigation that can either confirm there is something to worry about, or completely assuage any fears people might have about Wi-Fi."

Lawrie Challis, chairman of the Mobile Telecommunications and Health Research Programme (MTHR), which is responsible for investigating the health effects of mobile phones, also welcomed the study. "All the evidence is that the exposures are going to be very small, but nevertheless there haven't been enough measurements made, particularly in places like schools, and it'll be reassuring to know that's the case."

A recent report from the MTHR found hints that using a mobile phone regularly for a decade or more may increase the risk of two forms of brain tumour.

"If the exposure from Wi-Fi turns out to be less than that from mobiles, then you wouldn't expect any health effects to be worse. But first you need to look at what the exposures are, and then if there are surprises with Wi-Fi, you need to think what health studies need to be done."