Tsuyoshi Hondou, a physicist from Tohoku University in Sendai, Japan, who is currently working at the Curie Institute in Paris, says Japanese commuter trains are often packed with people surfing the Web on their mobile phones. The trend spurred him to find out what effect this had on the electromagnetic radiation in a train carriage.
Starting with plans of a typical train carriage acquired from a Japanese train operator, Hondou worked out the ratio of window area to structural metal for a typical carriage. He then used this to work out what proportion of the microwave radiation from the cellphones would be transmitted out of a carriage through the windows and how much would be reflected back inside.
Hondou then calculated how microwaves from mobile phones distributed throughout a train carriage would add together, much like light from different lamps would increase the overall illumination in a room.
He found that when both reflection and the cumulative effect of the radio waves were taken into consideration, the resulting electromagnetic field in a train carriage could exceed the maximum exposure level recommended by the International Committee for Non-Ionising Radiation (ICNIRP). "It's possible even if the train is not crowded," Hondou told New Scientist.
For a standard train carriage, with a carrying capacity of 151 people, Hondou's calculations show that it's possible to exceed ICNIRP exposure limits if 30 people, each with a mobile phone that emits radio waves at a power of 0.4 watts, all use their phones at the same time. The peak power a mobile phone is allowed to produce is 2 watts.
Hondou says his findings point to what could become a new environmental issue, especially as new wireless devices and laptop "connections" come onto the market. He suggests train operators should take notice. "At the moment, we have no regulation on the use of mobile phones in areas where many people are together," he says. The problem could also arise on buses and in some types of lifts (elevators), he adds.
Les Barclay, a radio engineering consultant who was part of the British government's Stewart enquiry into mobile phones and health risks, is cautious over Hondou's findings. While he concedes microwaves will bounce around inside carriages and boost field levels, the increase should be minimal, because power drops off a short distance away from each phone, he says. But Hondou counters that the drop-off Barclay refers to is only realistic if the radio waves aren't strongly reflected by the train's walls.
Author: Ian Sample
More at: Journal of the Physical Society of Japan (vol 71, p 432)
New Scientist issue: 4th May 2002
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