Summary
There has been plenty of media coverage of WiFi and the
potential dangers in 2007. There is a lot of misunderstanding
and misrepresentation of evidence being thrown into the mix, and
it is becoming very hard to follow the strands of a) what the
exposure levels are, b) what the evidence is actually saying,
and c) what other aspects need to be considered on WiFi.
Many of the concerns were summarised in a Memorandum on WiFi
signed by eight members of the Health Protection Agency's
EMF Discussion Group and sent to the HPA at the end of 2007
following the announcement of research, costing about £300,000
of public money, which does not address any of the health
concerns. The HPA have chosen not to respond to this Memorandum,
so on 25 April 2008 a copy has been posted here for members of
the public to read. [Download
in full] 9 pages, 73 KB
Schools without Wifi
On request, we have started collecting a list of submitted
schools that are confirmed to have (or not have) WiFi installed.
Due to obvious restrictions there is only a very small
proportion of schools represented, but in case it may be helpful
you may want to look through
our current list.
General Exposure Levels
Michael Clark, senior HPA spokesperson, has publicly stated
that "Being on a phone for 20 minutes is equivalent to 1 year in
a WiFi classroom". This is both factually incorrect and highly
misleading.
Whilst Mike Clark is right that a mobile phone, working on
full power and with you talking continuously (not listening) can
technically expose you up to about 50% of the SAR limits. In
normal use, with a good number of signal strength bars showing
on the display (say 75% signal level), the phone will be working
at somewhere between one-thousandth and one-twentieth of this
level. Let's average this at about one fiftieth as a reasonable
level for the phone to be operating at most of the time. Then,
if you are talking 50% of the time, this would reduce the
transmitted pulses (using DTX) by another factor of 2. So, a
typical exposure would not be 50% of the SAR limit but more like
0.5% of the SAR limit which we should assume to be 0.5% of the
the ICNIRP limit (for a typical call).
11/10/2007 - This has been updated to
more accurately reflect expected real life power outputs from
Wireless access points in use.
Now we come to a slightly different exposure regime in the
classroom in that you are not holding the wLAN card to your
head. 2.4 GHz wLANs (most common in the UK) operate at 0.03
watts output power (5-6 GHz ones can use up to 20 times this).
So we have one wLAN node in the classroom (0.03 W) and, say, 20
laptops all at 0.03 W. However, they are only transmitting much
power when actually transferring files. So, let's say that we
have the equivalent of one laptop operating absolutely
continuously (actually the combined output of 20 may well be
more that this), and that we are on average 2 metres from the
antennas. This seems reasonable based on the fact that there are
20 in the room. So E = (sq.root (30*0.03*2))/2 = 0.67 V/m
equivalent continuous. Now the ICNIRP guidance at 2.4 GHz is
61.5 V/m. So the signal strength is about 1/100th of what is
allowed. Power is proportional to signal strength squared so
that would be around 1/10000th of the ICNIRP power level.
So, we have a mobile phone call next to head typically 0.5%
(1/200th) of the ICNIRP guidance. We also have being in a 20 PC
wLAN classroom being something in the order of 0.01% (or
1/10000th) of ICNIRP guidance, about a 50-fold difference.
Therefore 20 minutes on a mobile phone running at typical
power levels would be equivalent to about 16 hours in a
classroom with 20 wLAN PCs, approximately eight standard school
days.
These figures have been updated from our "dispelling the
wireless myths" news article as 1m seems an unreasonable average
distance from the laptops. However, we have encountered a number
of access points that are sending short bursts of data a few
times per second, and the signal strength of these are all
reasonably high - If this is the case, the average exposure from
any access point will be much higher than in the calculations
above.
However, these figures are assuming that it is cumulative
absorbed power that is being implicated in RF research, and that
then implies a linear dose-response relationship model. From the
evidence that has found a risk, this seems unlikely to be
the case. Peak signal strength received may also be important,
and people using WiFi enabled laptops would regularly be exposed
to electric fields of 2 to 3 V/m. Whilst this is far below
ICNIRP, it is far above the levels where adverse health effects
are being reported (~0.05 V/m).
It is also an interesting contrast to our own HPA, as
highlighted by a
recent correspondence between Michael Clark and Dr. Grahame
Blackwell.
Scientific Evidence
Firstly, it is very important to stress that there is
currently (as of July 2007) nothing that we are aware of in the
scientific literature that looks at WiFi. So initially the
answer would be "none". However, when anecdotal evidence of
problems are being reported, it is prudent to do two things:
Firstly, prioritise research to be done looking specifically at
effects from typical WiFi exposure, and secondly, to have a look
at the literature published on exposures and technologies that
may be relevant.
TV and Radio Transmitters use relatively similar frequencies,
but are not digitally pulsed transmissions (AM and FM radio are
entirely continuous wave and TV is almost entirely continuous
wave). There is a reasonable chance that, if humans react to TV
and Radio transmissions, it may be very differently to the
reaction to a digitally pulsed signal, so even though there is
evidence of a possible risk[1]
these may not be relevant to WiFi.
Mobile Telecommunication systems (CDMA, GSM and 3G) are both
closer in frequency and are also digitally pulsed information
carrying signals - these are sufficiently close to WiFi that the
research into phones and their base stations may be applicable
to exposure from WiFi.
Firstly, typical exposure from a phone in use is likely to be
far higher than from a typical WiFi laptop or access point due
to the different in proximity to the device in question. So
whilst, again, there is research showing that there may be a
risk[2][3], this may not be
relevant.
However, signal strength from a mobile phone base station
where it reaches the ground (approximately 70 to 100 metres from
the base station) is typically between 0.5 and 1.5 V/m, exactly
the same as we measured in a WiFi classroom in a school in
Norwich, and the same as found in the above calculations, and
seems therefore to be very relevant. A quick survey of the
literature looking very specifically into mobile phone base
station epidemiology finds some statistically significant health
effects[4][5][6][7][8][9][10][11][12].
Many of these are summarised, with helpful graphs, etc, in our
subscriber article
"Radiofrequency EMFs and health risks". There is, in fact,
very little research looking at base stations that has failed to
find an effect. Also interesting is that many of the effects in
the papers above (non-cancer effects) are those being reported
in the anecdotal evidence from WiFi exposure.
In essence then, there is sufficient evidence to warrant some
degree of precaution regarding WiFi until research has been done
very specifically into its effects. With dLAN systems and
ordinary CAT5/6 wired networks offering better stability,
bandwidth and security, there is simply no need for most homes,
organisations and schools to switch to wireless networks, apart
from the savings of the slight inconvenience in cables.
The HPA have recently announced a £300,000 study into
measurements of typical WiFi system exposure levels. We have
noticed however that this research has already been repeatedly
been done, and we have provided a
short summary of said research for those interested.
IT Practicalities
As briefly mentioned above, there are other serious drawbacks
to using WiFi that are important considerations when
implementing computer networks. Firstly, the bandwidth is really
not very good. Modern wired network cables are running at 1 GBit/sec,
and even older networks are running at 100 MBit/sec. WiFi on the
other hand typically performs at around 8-15 MBit/sec, even
though the specs suggest it should be capable of about 54 MBit/sec.
On top of the speed restriction, WiFi is also susceptible to
interference. An access point is typically only designed to
accept concurrent connections from a handful of laptops, else
the system can easily start getting confused. Likewise, it is
easy to disable a network by blasting the area with higher
powered 2.4 GHz radiation. Then lastly, and from an IT point of
view, is security. Without technical knowledge, many access
points come without having WEP encryption set up, and not doing
so can leave your wireless network very vulnerable to intrusion
from other wireless devices. It is very easy to drive around a
city residential area, and with the right hardware, find an
unsecured wireless network adaptor and simply "hook in" to
someone else network and internet connection. Aside from the
usage of their payed for bandwidth, this has a risk of letting
them access files on other computers on the network, and also
performing illegal activity whilst effectively framing the owner
of the internet connection. Again, wired networks are simply
secure unless someone comes into your house and plugs a laptop
of theirs into your router / switch.
Having said this, Wireless network does have the rather
useful advantage of not having to cable up various rooms in your
house (where you would intend on using a laptop) with networking
sockets. However, again, there is a more secure and stable
alternative, at pretty much the same price: dLAN units allow you
to use the buildings mains circuitry as an extension to your
computer network, so all you have to do is plug one dLAN unit
into the wall (and network to your router / wired network) and
the whole building is networked. Plug the other unit into any
other socket on the same power circuitry, and voila, you have a
new network connection. Because the network traffic is still
travelling down wires, and it doesn't get out beyond the house's
consumer unit, the network is secure from those that do not have
physical access to the house itself. It can also carry a higher
bandwidth than a wireless network (typically 80 MBit/sec).
So there really is no need to use WiFi anyway, barring the
convenience of not having to plug your laptop into anything at
all (but for those that need a mains socket anyway, dLAN just
uses one extra wire from the same socket as the laptop adaptor).
For schools we would recommend wiring up all the classrooms that
need to have network access, preferably by putting the power and
network cabling through the same trunking. If done by IT staff,
this is a lot cheaper than wireless networking equipment anyway.
If there is no-one capable, or allowed (perhaps on health and
safety grounds), again dLAN is the next best option as this
reduces the need for expensive sub-contracting work.
Other Resources
Dr. Magda Havas (Environmental and Resources department,
Trent University, Ontario, Canada), has written an excellent
precautionary paper, prepared for the Board of Supervisors, City
and County of San Fransisco. This 51 page document is available
from
here, and covers a wide range of literature and scientific
findings on RF research, and presents them in a logical and
progressive manner.
Concerned parents Jane Smith and Vanessa Spedding have
recently fought a successful campaign to prevent WiFi being
installed in Wigmore Primary School, Herefordshire. Their
campaign succeeded using a common sense approach combining
precaution against the possible health effects, cost, and IT
practicality. They are happy with us presenting
their letter, an accompanying
letter from Prof. Olle Johansson, and a
full implementation costing from an IT company that installs
network systems. It is also important to note that, contrary
to the text in the letter, many schools in Canada do still use
WiFi for their classrooms.
BECTA have provided a very thorough albeit
technical article on WiFi and wireless specifications. |