Daily Telegraph – 6th December 2003
By David Derbyshire
What is Tetra?
Tetra stands for the Terrestrial Trunked Radio system – a secure digital radio system being connected across Britain for the emergency services, the military and companies.
Where are masts being erected?
O2 Airwave, the company creating the police’s Tetra, is installing 3,350 base stations on masts and buildings in Britain.
How does Tetra work?
It uses radio signals broadcast at 400MHz. Base stations relay signals to and from handsets. Four users can broadcast on the same channel simultaneously by confining transmissions to “bursts” at 17.6 times per second (Hz).
The health concerns?
There have been reports that early users suffered headaches, sickness, migraines, disturbed sleep and skin rashes. People living near masts say they have suffered similar stress-like symptoms. Some campaigners have expressed concern at the 17.6Hz frequency used by the handsets.
What’s the evidence?
There are two possible risks to health from a radio frequency radiation – a heating effect on tissue and a non-thermal effect on cells. The first is well established, well researched and governed by international regulations. The second is poorly understood.
What is the evidence for a heating effect?
Prof Colin Blakemore, the head of the Medical Research Council and a leading brain researcher, says the heating effects are negligible more than three feet from the antenna. Because the beam is pointed away from the ground, exposure below the mast is also negligible. About 100 yards away, the point where the beam usually reaches ground level, the radiation is several hundred times weaker than the radiation from a mobile phone next to the head, he says.
Tetra handsets typically emit radio-frequency radiation at a peak of 0.25 watt – within safety guidelines. But if four signals were sent simultaneously from a handset, the signal would be more powerful.
What is the evidence for non-thermal effects?
Studies on dead chick brains in the mid-1970s appeared to show that low-power 16Hz radio frequencies – similar to those used in the handsets – triggered movement of calcium ions in cell. Calcium plays a crucial role in nerve tissue.
Further studies of 16Hz frequencies, including some at the Defence Evaluation Research Agency at Porton Down, have been contradictory.
Prof Blakemore says that the early studies were not well designed and have been hard to reproduce. The significance to health is therefore unclear.
The industry says that the masts emit frequencies around 400MHz and do not pulse. But campaigners say they do.
What is the official line?
The chick research was highlighted in a report on mobile phone safety in May 2000, under Sir William Stewart’s chairmanship. He said 16Hz should be avoided in mobile phone systems.
A major report into Tetra from the National Radiological Protection Board in 2001 concluded that the system was unlikely to pose a health hazard, but said it had “too many limitations” to give assurance of no hazard.
Are scientists concerned?
Dr Gerald Hyland, a retired theoretical physicist at Warwick University, says some radio frequencies interfere with the natural “resonance” of cells and could be harmful. Most mainstream biologists and physicists disagree with him.
Why do protesters cite the Salzburg resolution?
In 2000, 19 academics gathered at an international conference proposed new rules for mobile phone and radio base stations. They called for exposure to radio frequency radiation to be kept at levels 9,000 times lower than guidelines from the International Commission on Non-Ionizing Radiation Protection.