Y Safle

A while back I wrote on a wave of Wi-Fi hysteria in the media. Since then the agitators have gone quiet, but I have been asked more than once for authorative guidance on the subject, so I am linking here the WHO factsheets on the issue.

WHO Factsheet on Electromagnetic fields and public health - Base stations and wireless technologies

WHO Factsheet on Electromagnetic fields and public health - Electromagnetic Hypersensitivity

The media is working itself up into a feeding frenzy again. This week’s issue: the alleged dangers of WiFi radiation. First BBC Radio news, then Newsnight, now the Daily Telegraph have all had articles from quoting from people who believe that there might be health risks from WiFi. The BBC programmes at least balanced the sillier claims by noting that WiFi power output is far lower than that from mobile phones.

The Daily Telegraph, on the other hand, had this nonsense:

However it is believed that a classroom containing 20 laptops and two routers could combine and be equivalent to the emission from a mobile phone.

Notice the use of passive voice: “it is believed”. Who believes this?

It turns out that no-one does, although the Telegraph quotes from the “Powerwatch” web site. On this site, there is a calculation designed to show that a room full of 20 computers and an access point (or two) is approaching the power output of a mobile phone call.

But this is arrant nonsense. It is nonsense because of the silly assumptions being made about average distance from antennae. It is nonsense because they first make an assumption of low power output from the phone, and it is especially nonsense because it makes no difference whether you have one computer or fifty in a room. The maximum power output is the same - capped in the UK at 100mw (but usually less than this).

Let me explain: WiFi stations are receiving a radio signal when they receive data. But if two stations transmit a signal at the same time then what occurs is a collision - the signal is garbled and not received. The solution is that WiFi uses a collision avoidance scheme to try to ensure that packets are never sent out whilst another station is already transmitting. A couple of carrier sense mechanisms are used to do this, and the result is a very low collision rate. Essentially, if one station is talking, all the other stations are quiet. Click on the thumbnail image to see how this looks in practice. Each wireless station waits a random amount of time before transmitting, and if another station transmits first, the wireless station will quietly defer to it.

Therefore the maximum power output from a room of 20 computers remains capped at 100mw. What is more, no one station is transmitting all the time. For the majority of the time, even on a congested network, each station is actually transmitting nothing.

And that brings us to the next bit of nonsense - the assumption of the amount of traffic in transit. The powerwatch page assumes more than 100% usage for periods of two hours or more in its calculations. Note that if a single wireless station on an IEEE 802.11g network were downloading constantly (and that the downstream network could maintain the same throughput), then even assuming protocol overheads reduce the actual throughput to a mere 30 Mbps, over a course of two hours, that station would download some 26 Gigabytes of data.

To put this in perspective, fairly heavy Internet users download about this quantity of data in a month. Light users (people just browsing the web, using email and similar) would not get close to this figure.

26 Gigabytes is the equivalent of about 44 CD images, or several thousand podcasts. It is a guge quantity of data - not the kind of thing people will be downloading in one sitting - and certainly not regularly.

Ah, you say - but spread between 20 computers? What classroom environment is encouraging pupils to download over a gigabyte of data per computer? None!

So the assumption of 100% utilisation is nonsense.

Next problem: The assumption is made that people are - on average - a metre from the transmitting antenna.

This is just silly. The writers seem to know that magnetic fields decrease by the square of the distance from the antenna, but they assume that on average, people are a metre from the emitted radiation. Based on the fact this is a classroom, and 20 stations are variously transmitting, the fact that some of these transmitters will be many metres away only really makes this assumption if the pupils have swallowed the transmitter.

Admittedly, I wouldn’t put this past some children - but if they have done so, they probably have worse problems to deal with than the emitted signal from the station!

No, in fact the vast majority of the transmissions come from the access point. (Remember, we download much morethan we upload) this may not even be in the class, but if it is, it will probably be several metres from even the nearest child. The law of squares tells us that these signals will be far lower than the silly assumption made on the powerwatch page and repeated uncritically by the Daily Telegraph.

As one commentator on the Telegraph page says:

“Can there ever be a better example of why the current decline of Physics teaching in schools and universities is so worrying?”

Let’s give the last word to Mike Clark, senior spokesperson for the Health Protection Agency. He has run the figures rather more intelligently than the Powerwatch pressure group, and tells us that 1 year of exposure to WiFi radiation in a classroom is equivalent to 20 minutes on a mobile phone.

Maybe we could quibble and bring that down to a month or so. So what? The worry with mobile phones is that the radiation causes excitation of water molecules in the brain near where the phone is held to the head. This causes a slight warming effect which could theoretically be a cause for concern, although there is no proof of harmful effects.

WiFi radiation - if it causes any warming at all - is so slight as to be unmeasurable.

There is no risk here.

The Western Mail recently reported in slightly hysterical tone that wireless computer networks should be banned from the nation’s classrooms because of fears about their effects on health.

MP Urges Ban in WiFi Technology in Schools

Why should we ban WiFi in schools? The reasons we are being given are that parents are concerned; that we don’t know the effects of WiFi microwave radiation yet; that one teacher claimed to be getting ill whenever teaching in front of a transmitter; and that we should apply the precautionary principle.

The result? Ysgol Pantycelyn in Carmarthern switched off its WiFi network (despite the benefits these networks bring to teaching). A few other schools in England have similarly shut down their wireless networks.

Now all of the reasons above suffer from a failure to consider the scientific basis for the claims being made. They show our penchant for listening to anecdotal evidence and rating it much more highly than scientific evidence. This is a dangerous error in our thinking. We are geared up to accept personal testimony, even though such testimony is necessarily limited and often flawed.

Who can argue that there is a problem if a teacher is feeling ill when teaching in front of WiFi equipment?

Except it turns out that in a controlled experiment when the access point was sometimes off and sometimes on, but the teacher in question did not know when it was off, he continued to claim to be feeling ill when he believed (wrongly) that the access point was on.

But that spoiler won’t be widely reported. No studies have indicated that people can detect WiFi radiation.

Someone will reply that the wavelength of WiFi radiation is in the microwave band is it not? So much so that microwave ovens are one of the largest sources of interference to WiFi equipment. So aren’t we cooking people by emitting this radiation?

Look - there is a clue here in the word “interference” above. If Microwave ovens are causing interference then they have been emitting some microwave radiation (more than from access points) for many years. Have we banned microwave ovens yet?

No, because the levels of emissions are essentially harmless.

How do we know?

Because we are surrounded by microwave radiation wherever we go. I suppose we could go and live at the bottom of a deep shaft mine to avoid it. But then we would probably die of vitamin D deficiency instead.

For people living on the surface of the Earth, we are constantly bombarded by radiation at every wavelength (including plenty of microwave background radiation).

And here is the important point. In the UK at least, WiFi radiation is strictly limited to 100mw (the limit is higher in the US). That limit has a very specific purpose. It means that unless you pretty much swallow the WiFi antenna, you are not going to absorb any more radiation from the WiFi network than from the background radiation.

What is more, the signal itself is deliberately encoded to look just like background radiation. The signal is spread over several wavebands to keep the power down, and “chipped” so that it looks just like microwave “static” unless you know what to look for and how to decode it.

And the power is kept so low so that multiple users of the same wave bands can coexist. Unlike mobile phones, for instance, which use much higher powers because the cell network has exclusive use of the waveband, and does not want to put base stations every 100 metres!

So there is no scientific reason at all to suspect WiFi networks. This is the advice given by government agencies and many local authorities (although some wash their hands of the affair with useless “advice” that it is “up to the individual schools”). We don’t need to worry about the safety of WiFi networks.

But all people hear is the anecdotal story (without refutation), and the words “radiation” and “developing children”, and it won’t be long before we see a wrong headed national campaign by some newspaper to ban this dangerous hazard in our schools.