Cellphone versus radio- spark risk

[Genghis the Engineer]

I was told the other day that on safety grounds, the refuellers on an airfield I frequent are banned from carrying mobile phones, so instead are issued with small "walkie-talkie" type portable radios.

Electronic engineering has never been my strong point - can anybody explain if/why there's a difference in spark risk between the two? Or is this a classic case of 'elf.n.safety regulations being produced by somebody who only half understands what they're doing.

G

[Captain Smithy]

Cellphones transmit over microwave, whereas walkies are VHF/UHF.

Microwave energy causes dielectric heating, hence the risk of ignition of fuel vapours.

Never heard any cases of this actually happening but best to be safe than sorry, I think.

Smithy

[bizdev]

I seem to recall a Mythbusters episode where they tested the 'Myth' of mobile phones igniting fuel vapour in a petrol garage. If I recall the myth was 'busted'.

[rudderrudderrat]

I believe it'd all down to "approval". Tests are done with say a "walkie-talkie" using a known frequency spectrum, power etc. and then approved.

Unless they tested every new mobile telephone produced on the market (just in case there is a glitch with one which opens a fuel valve and causes a fuel spill etc.) - then the simple solution is to ban them all.

My ancient Nokia mobile phone will tune the VHF radio select frequency randomly when it's placed near the controller on the flight deck. Who knows what it would do near the refuel select panel?

[One Outsider]

Another thing to consider is that much of the stuff sold as and marked as compliant with EC or FCC regulations in fact are not.

[Captain Smithy]

bizdev

I wouldn't be surprised if the myth was busted. Anyone remember the fake video of the egg supposedly being "cooked" between two mobile phones?

Mobiles are very low-power RF sources. Although I'd still err on the side of caution.

Smithy

[nightmode]

Having designed mobile phones and mobile radios I often wonder about the risks supposedly caused as well.
GSM900 maximum transmit is 2W, pulsed at 217Hz (hence the buzzing near speakers etc).
UHF mobile radios are anywhere between 1W to 5W, continuous transmission when keyed, FM modulated.

Weird effects on electronics is mostly due to poor design for RF field immunity, the bursty nature of GSM tends to annoy general electronics more than a continuous carrier.

In a 50 ohm system (most mobile antennas), 2W of power gives 10V of potential in the antenna. Noting that the breakdown of air is in the order of 3000V / mm. You can draw your own conclusions ..

That said, I think that hitting the battery to pieces with a hammer and getting a lithium fire is a more likely ignition source :8

[twochai]

I suspect the greater risk is of a ringing cellphone distracting the refueling operator from the task at hand.

Anybody notice the recent case of an engineer buttoning up the cowling on an E-190 being distracted by a phone call at a critical moment and forgetting to engage the cowl locks?