How Bad Can Wi-fi Be?

An anonymous reader writes "Sunday night in the UK, the BBC broadcast an alarmist Panorama news programme that suggested wireless networking might be damaging our health. Their evidence? Well, they admitted there wasn't any, but they made liberal use of the word 'radiation', along with scary graphics of pulsating wifi base stations. They rounded-up a handful of worried scientists, but ignored the majority of those who believe wifi is perfectly harmless. Some quotes from the BBC News website companion piece: 'The radiation Wi-Fi emits is similar to that from mobile phone masts ... children's skulls are thinner and still forming and tests have shown they absorb more radiation than adults'. What's the science here? Can skulls really 'absorb' EM radiation? The wifi signal is in the same part of the EM spectrum as cellphones but it's not 'similar' to mobile phone masts, is it? Isn't a phone mast several hundred/thousand times stronger? Wasn't safety considered when they drew up the 802.11 specs?"

Comments

WiFi is microwaves

[QuietLagoon]

Can skulls really 'absorb' EM radiation?

802.11b/g uses 2.4GHz radio waves. That's the same frequency range as microwave ovens. Microwave ovens work because the microwaves are absorbed by the bonds in the water molecules of food (which is why dry food does not cook in microwave ovens).

So yes, human tissue that contains water can absorb WiFi radiation. That is a fact.

What is not known is: how much absorption of that radiation is bad for the kids?

Re:WiFi is microwaves

[Andy Dodd]

I believe there is a scientific reason for the ISM band being there - I think water has a bit of an absorption peak in the 2.4 GHz region.

For this reason, 2.4 GHz wasn't too hot for long-haul communications due to water vapor in the air, so no one was in a rush to license spectrum for it, and no one fought designating it as an "Industrial, Scientific, Medical" band. (with the primary use in all three of those categories being to take advantage of that water absorption peak for heating.) Now, because the band is such a cesspool, no one minded allowing low-power unlicensed communications in that band.

Now, as to the health effects of this - Yes, the water in your body is more likely to absorb 2.4 GHz RF. No, that absorption will not do any cumulative damage. Absorbing 2.4 GHz RF will make the water molecules in your body vibrate a little more (i.e. it will heat you up.) At high powers, this does become dangerous as the heat basically cooks you from the inside (just like a microwave oven). At low powers (with 802.11 being a great example), the body is able to safely dissipate the heat rapidly enough so that not only is no damage done, the change in temperature at any point in the body is negligible. You're more likely to get burned by touching the heatsink of the RF amp than you are by touching a circuit trace carrying RF at those power levels.

RF radiation is nothing like nuclear radiation - the critical difference is that nuclear radiation is ionizing, that is to say that it can not only vibrate molecules a bit, but it has enough energy to alter them. This has the effect of "flipping bits" in your DNA and other such nasty stuff. Since "bit flipping" can have cumulative effects, low levels of ionizing radiation can be dangerous in the long term, because the damage accumulates. With RF, it doesn't unless power levels are so high as to induce temperatures that cause thermal damage.

Prior to graduate school, I worked at a company that built RF power amplifiers for cell towers (30-45W average power output), and many of my coworkers had been working with microwave RF amps since the very first cell system Motorola deployed. (Yes, we had some ex-Motorola old hands there, who had interesting stories from the early days when the system designers were also heavily involved with the installation process of new base stations.) No health problems whatsoever.

Since graduate school, one of the tasks of my department is taking equipment through EMI testing. We're frequently right at OSHA RF exposure limits - no health problems with any of us (Well, at least no new ones that weren't preexisting conditions), even our mentor who has been doing this for 20-30 years.

Re:WiFi is microwaves

[jmv]

Except, you know...the nuclear radiation that is RF radiation...which is all of it.

While gamma radiation is indeed electromagnetic, what pretty much everyone calls RF is actually whatever is below the infrared (i.e. microwave downward). Also, not all nuclear radiation is electromagnetic. Ever heard of alpha and beta particles -- those are ionising too.

What about UV? That causes mutations too. Does that have as much energy as gamma (the answer: not if the amplitude is the same)? This is just crap. Any kind of radiation can have three effects on cells:

What the hell is "amplitude" supposed to mean. This isn't about the amount of power, but the nature of the radiation (quantum physics 101). Either a certain radiation is ionising or it's not (well of course, there's a range where it depends on the exact molecule). For both UV and gamma, the energy of a photon is enough to eject an electron (or move it where it's not supposed to be) and thus cause damage to the DNA. For microwaves, you can pour as much energy as you like, it's just not going to happen. The only potential harm from microwave is the fact that it can potentially heat up the body (but it takes more than a few mW).

The more energy, the more likely to get #3. However, there are agents in the skin to absorb most of the energy in most of the RF spectrum. Any part of the spectrum can cause mutations if you can get it to do step #2 and not step #3.

No, mutations can only be caused by ionising radiation. A microwave oven will cook you, but it will *not* cause mutations because the microwave photons simply don't have enough energy to displace electrons. Also, why do you think we put sunscreen to protect our skin from UV radiation while leaving it fully exposed to infrared and visible light, which make up most of the total radiated power from the sun (and far more than UVs)?

Your story aside, that much power could easily burn someone to cinders if they happened to be sitting on the focal point of a microwave dish.

No, it will have about the same effect as using a 20 cm magnifier in the sun. Would probably hurt, but not kill you.