WE have had this question many times:
Mobile phones are blamed for all kinds of health problems, ranging from brain cancer to memory loss. There's not a lot of real evidence for this, so people don't seem to be worried, and it certainly doesn't stop them from using their phones. Mobile phones are also the cause of a lot of stupidity when in the hands of pedestrians and motorists. In fact, it's illegal to use a hand-held phone when driving a car. But strangely, most people won't use their mobile phone while they are refuelling their car's petrol tank - and in this case, it's even less likely to be dangerous.
Every month or so, I get an earnest email warning me of the hazards of using my mobile phone on the forecourt of a petrol station. Usually, the email mentions the Shell Oil Company as its source, and quotes the same three incidents of petrol fires while refuelling. The first one has the mobile phone sitting on the boot - the phone rings, generating an instant ball of fire. The second episode has a person speaking on the phone, leading to nasty facial burns. The third occurrence has the phone in the pocket suddenly ring, causing unfortunateß burns to the groin and thigh.
This email has been traced back to a hoax email that landed in the inbox of a Shell employee in Jamaica . He rebroadcast it, but with the Shell Company signature now on the email - and this accidental non-approved signature gave the hoax more credibility.
So, has a mobile phone ever set off a petrol station fire? No, according to the Australian Transport Safety Bureau, who looked at 243 petrol station fires worldwide, happening in the 11 years between 1993 and 2004. And no, according to the Australian Mobile Telecommunications Association, and no, according the Robert Renkes, a spokesman for the American Petroleum Institute, who said, “We have not found a cell phone responsible for any fire since the beginning of mankind” . And finally no, according to the popular Mythbusters TV show, which tried mightily to make a mobile phone explode a chamber full of petrol vapour, and failed.
It is theoretically possible to set off a petrol fire with a phone. The amount of energy needed for a spark to ignite petrol vapour is 0.2 mJ, which is roughly one five-millionth of the energy stored in a fully-charged phone battery. The difficulty is that the phone is not designed to make sparks.
The lithium battery could explode while charging if its internal regulator circuit was very faulty. But you don't normally simultaneously charge and talk on your mobile phone while refuelling your car. The internal electronics of the phone could fail and make a spark - but the spark would be too small.
And why worry about the phone battery when you have batteries in your iPod, CD player, mini-torch, and yes, don't forget the big 15 kg car battery that powers the electrics of your car?
Well, what about the electric field put out by your phone? Yes, the electric field has been measured at 2-5 volts/meter, and has been known to interfere with heart monitors and infant incubators in hospitals, and various electronic equipment in planes. But the electric field from a mobile phone has never been known to set off a fire in a petrol station. And consider that in the UK , some 200 Shell petrol stations have mobile phone towers in the tall petrol price indicators, which stand right there on the forecourt, a few metres from the petrol pumps. The towers put out a lot more grunt than your small mobile phone.
So what did set off those 243 petrol station fires? Most of the time, static electricity was the culprit. We've all seen or felt a spark from clothing. If you are wearing synthetic clothes in the dryness of winter, and are sliding in and out of the car, across the synthetic material of the car seat, then you can build up a big static charge. Then, if the earthing wire on the petrol hose is broken, when you touch the metal nozzle of the petrol hose to the metal neck of the petrol tank, you can discharge a visible spark. Even more dangerous, from the static electricity point-of-view, is filling up a small fuel drum.
The phone companies post warnings about using phones in petrol stations for two reasons. First, mobile phones are not designed with “Intrinsic Safety” to make them able to operate safely in truly hazardous inflammable vapour situations, and second, fear of legal liability, despite all the evidence showing that mobile phones don't cause fires in petrol stations.
So overall, the mobile phone myth is just endless chatter generating a whole lot of static.
© 2008 Karl S. Kruszelnicki Pty Ltd
Published 30 November 2006