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WiFi in EMF sensitive environments

Can anyone tell me whether WiFi networking is permissible in hospital wards? My local acute hospital insists that everyone turns off their mobile phone one entering, the published explanation being that the signals that phones regularly send to inform the network as to which cell they are in can interfer with monitoring and other equipment. This is the same explanation as given by airlines and may just be precautionary rather than a serious threat to safety.
Even so, if it's true for phones, is/will it also hold for WiFi frequencies/energies?

David Roper
Saturday, April 26, 2003

If it's in the same frequency band, I'd steer clear.

If it's in  different frequency band, I'd steer clear.

www.marktaw.com
Saturday, April 26, 2003

We have some old, old language labs and we play tapes from a tape deck throuigh two wall speakers. If the students have the mobile phones switched on, even though they are not being used, the interference comes through the speakers and makes the tape uniintelligible.

When I was at colllege all the police walky-talkies used to come through the stereo. Great if you wanted to avoid being busted!

There are some reported  cases of input put on HP wireless keyboards being inputted on computers five or ten houses down the street.

I have two Satellite TV decoders that come from the same manufacturer, though they have been customized for each separate digital package. There is no way I can remotely change channel on one decoder without digitally changing it on another.

Stephen Jones
Saturday, April 26, 2003

802.11a almost certainly is not interfering with anything, as it's 5GHz. 802.11b and g, on the other hand, live in the rather noisy and crowded 2.4GHz band. Cell phones do not operate in either band, though.

Brad Wilson (dotnetguy.techieswithcats.com)
Saturday, April 26, 2003

david, the hospital where I work does have a WiFi network in the wards.

choppy
Saturday, April 26, 2003

Re: cell phones in airplanes:

There's no evidence that cell phones affect plane equipment. The main reason they ban cell phones is purely economic: the airlines receive a cut of the revenues from the telephones installed onboard.

http://zdnet.com.com/2100-11-501431.html?legacy=zdnn

raindog
Saturday, April 26, 2003

You need to work closely with the hospital's biomed department. I've worked on medical equipment before (an EEG monitor called the Neurotrac II). Depending on the equipment, some of it (especially EEG gear) can be VERY sensitive to noise. And radio signals can do all sorts of wierd and unexpected things inside a building, some of which can cause a very high-frequency signal to alias down into very low bands and interfere with things that you wouldn't expect.

In short: Have a long heart-to-heart with the hospital's biomedical engineering folks (the ones who put a 'safe for patient use' sticker on every piece of equipment). They can give you the best advice. If it's feasable, consider avoiding wireless unless you are sure what sort of gear is going to be in use.

My one, true rule for dealing with medical gear: Would you let them put you in that ward/use that thing on you? If not, you've screwed up - start over.

(Yes, I did have my EEG done by our in-house people. I also had an evoked potential study done by our folks, using our gear, as part of evaluating the equipment.)

Michael Kohne
Saturday, April 26, 2003

I think the cell phone rule on airplanes is an FCC rule, not an FAA rule.  It's not designed so much for interference with flight systems, as it is to prevent problems or "free calls" on cellular networks when you're up at 30,000 ft.  From there, you're within line-of-site of thousands of cellular towers. 

I've read reports of people not getting charged for cellular calls at that altitude because the cell-switching software couldn't keep up with the speed with which calls were passed from cell to cell. 

Robby
Sunday, April 27, 2003

On the hospital issue (which was the original question anyway), I would hope that all electronic hospital equipment is tested to be resistant to any publicly available frequency spectrum.  Since WIFI operates in such a frequency theoretically those devices should be OK. 

Robby
Sunday, April 27, 2003

Thanks everyone.

I would like to think that critical hospital equipment would be built to be as immune to RF interference as possible, not least because all those CRT screens, fluorescent lights etc. etc. are themselves RF emitters. You'd hope that any analogue cable runs used shielded cables and that digital protocols would be robust against the occasional interference induced glitch.

What caught me by surprise recently was a fault with my ISDN connection. When British Telecom came to fix it, it transpired that their standard cable doesn't use shielding around each pair to avoid crosstalk. Instead, each time they step from one run of cable to another they just switch around the conductor pairs so that crosstalk induced between between different cable pairs tends to cancel. Well, this may be OK for a voice circuit as it'll just get a bit more hiss and crackle, but it sure doesn't work for digital unless everything else is perfect!

David Roper
Sunday, April 27, 2003

It would be nice if all hospital equipment were relatively immune to RF interference, unfortunately for a lot of things (EEG and heart monitoring at least) you are measuring electrical signals in the patient. To do so, you effectively make the patient part of the circuit. Since humans are (unfortunately) rather good antennas, and grounding is shaky at best in these things, you can't avoid some amount of RF getting into the mix.

Michael Kohne
Monday, April 28, 2003

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