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Last Updated: Friday, 5 November, 2004, 18:29 GMT
Mobile phones as fire risks
Spencer Kelly
By Spencer Kelly
BBC Click Online reporter

Spencer Kelly has been looking at places where mobiles are discouraged, and finding out why.

No mobiles sign
Use of mobile phones is prohibited on petrol station forecourts
At home, at work, in the street - mobile phones are everywhere, or so it would seem.

But they have not quite invaded every part of our lives.

There are still places where the mobile just is not welcome.

One of these mobile-free zones is the petrol station.

Using a mobile here, we are told, could cause sparks and ignite petrol fumes on the forecourt.

And we all know how unpleasant that could be; sparks and petrol vapours do not a happy couple make.

A mobile phone is a battery-operated radio transmitter, and as such there are a couple of ways it could, theoretically, generate a spark.

If radio waves are powerful enough, they can induce a current in a nearby metal object.

That is sparks to me and you.

If, for example, you put a light bulb in a glass of water then popped this in a microwave and turned it on, the radio waves emitted would be strong enough to light the bulb.

(Needless to say, this experiment should not be tried at home.)

Spencer Kelly
Even in remote locations, mobiles only generate about two watts
The question is, can a mobile phone do the same kind of thing as a 900 watt microwave?

Dr Stepan Lucyszyn, an electrical engineering specialist, says: "Under normal operations a mobile phone generates about one watt of RF power.

"This is enough for normal use in and around town, but sometimes in remote locations you have to ramp up the power a little bit to one and a half or two watts, but two watts is really your maximum.

"Mobile phones just don't have enough power transmitted to create a spark with enough energy to cause ignition."

Explosive potential

But even if a normal phone transmitter is not a danger, what about the more obvious suspect - the battery?

Dr Lucyszyn says: "If the mobile phone is switched on, and you're changing the battery midway through transmission, then there's quite a lot of current flowing through the battery.

"If you then disconnect the battery you'll find a spark, just momentarily, but there's enough energy within that spark to cause the [petrol] vapour to be ignited."

Phil Thomas, a trading standards officer, adds: "The main hazard is that you may drop the phone, the battery becomes disconnected, causing a spark which could ignite the vapour around the car."

But of course mobile phones are not the only battery-operated devices we are carrying around nowadays.

Are things like iPods or laptops also a danger?

Dr Lucyszyn says: "MP3 Players usually don't have much current going through them; they're usually very low voltage.

Should the wearing of stockings be prohibited in certain places?
"I believe you have just as much risk from changing the battery in a laptop computer as you do in a mobile phone.

"Indeed, most laptops actually drive a lot of current through the battery and if you break that connection you could potentially have an explosive situation."

Phil Thomas is not sure whether there should be signs at filling stations about the use of laptops.

"I think we'll have to see how things develop. At the moment I don't think it's a particular problem.

"If it takes off in a big way and people start using their laptops on a forecourt on a regular basis we may well have to look at it again."

So although it is unlikely, under certain conditions mobiles and laptops can spark. And it is best not to be around petrol vapour when they do.

That said, there has never been a proven case of this happening.

It is also worth noting that sparks can be caused by other sources too.

Phil Thomas says: "There's also a problem with clothing: things like nylon stockings, overalls, that kind of thing, which can build up static."

And Dr Lucyszyn adds: "You're more likely to get dangerous sparks from wearing nylon clothing than you are to get an explosion from a mobile phone transmitter."

Perhaps this calls for a new type of sign in our forecourts...

Click Online is broadcast on BBC News 24: Saturday at 2030, Sunday at 0430 and 1630, and on Monday at 0030. A short version is also shown on BBC Two: Saturday at 0645 and BBC One: Sunday at 0730 . Also BBC World.

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