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Passengers on packed trains could unwittingly be exposed to
electromagnetic fields far higher than those recommended under
international guidelines. The problem? Hordes of commuters all using their
mobile phones at the same time.
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Wireless
gadgets and trains may prove an uneasy mix (Photo: Getty) |
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.
Buses and elevators
For a standard train carriage, with a carrying capacity of 151 people,
Hondou's calculations show that it is 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 two 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 are not strongly reflected by the train's
walls.
Journal reference: Journal of the Physical Society of Japan (vol
71, p 432)
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