Never Mind the Bullocks, Here's the Science (22 page)

However, mobile phones are the cause of a lot of stupidity in the hands of pedestrians and motorists. It is well established that talking on a phone while driving makes you as incompetent a driver as if you were drunk. And that’s just talking on the phone, using a hands-free set. The mere act of concentrating on the phone call makes you a less capable driver. Holding the phone makes you even less capable. In fact, in some states around the world it’s illegal to use a hand-held phone when driving a car. But people will still do it.

Not surprisingly, given the little pictures displayed on petrol pumps, many people believe that mobile phones are dangerous to use while refuelling their car’s petrol tank. Yet there’s pretty much no evidence that using a mobile phone at a petrol station will set off a conflagration.

How much evidence? How about not even one case in the history of the human race, and that’s taking into account every single petrol station that has ever been built, in every country of every continent!

And yet people still believe this myth.

The Email

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. Almost every time, the email mentions the Shell Oil Company as its source, or has the Shell Oil Company in the ‘sig’ (signature) lines at the bottom of the email.

And almost every time, it quotes the same three incidents of petrol fires that occur while a mobile phone owner is refuelling the car.

The first incident has the mobile phone sitting innocently on the boot of the car, not far from the open petrol tank. The phone rings, generating an instant ball of fire.

The second episode has a person speaking on the phone while refuelling. Again, a conflagration ensues, leading to the person suffering very nasty facial burns.

In the third occurrence, the owner is refuelling when the phone in a pocket suddenly rings. Even before they answer the phone a fire somehow erupts, in this case causing unfortunate burns to the person’s groin and thigh.

This email (about mobile phones causing petrol station fires) has been traced back to a hoax email that originated in Southeast Asia around 1999. In June 2002, it landed in the inbox of a Shell employee in Jamaica. He rebroadcast it, but with the Shell Company signature now added to the email. This accidental, non-approved signature gave the hoax more credibility.

Mobiles + Petrol = the Big Bang Theory

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 – and it certainly doesn’t stop people from using their phones.

With many a warning sign at petrol pumps, there is a general belief that mobile phones are dangerous to use while you are refuelling your car’s petrol tank.

However, there’s pretty much no evidence that using a mobile phone in a petrol station will set off a conflagration.
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Tiny Seed of Truth

Like all good myths, this one has a tiny seed of truth in it.

Mobile phones get their power from their internal battery. Battery technology has always lagged behind electronics technology. Early mobile phone batteries had a few problems. They were heavy. They didn’t store a lot of energy. They would not recharge fully, unless they were flattened fully (the so-called memory effect). And after a relatively small number of cycles of ‘charge-and-discharge’, they would die.

In the 1990s, these batteries were NiCad (Nickel Cadmium) batteries. They were replaced by NiMH (Nickel Metal Hydride) batteries which, in turn, were replaced by Li (Lithium) batteries. As the phone battery evolved, it became more complicated. In fact, the lithium phone battery is a Smart Battery—it has its own internal electronics to stop it from being flattened so much that it suffers permanent damage, and to keep the charging time as short as possible, etc.

Thermal Runaway

One advantage of lithium batteries is that they are lighter. But many lithium batteries use cobalt oxide, which can undergo ‘Thermal Runaway’. According to the computer magazine
PC World
, ‘…when you heat this material up, it can reach an onset temperature that begins to self-heat and progresses into fire and explosion’.

Various experts recommend that you do not leave your laptop or mobile phone in the car on a hot day. A temperature of 60°C is enough to initiate Thermal Runaway.

Modern lithium batteries can store quite a lot of energy. They can keep a phone running for several days, slowly giving out this energy in tiny amounts.

But if all this energy were to be released in a fraction of a second, a lot of heat could be generated.

And yes, there have been cases of lithium batteries in laptop computers spontaneously overheating, warping the laptop’s case, scorching the wooden desk on which it had been left and even bursting into flame. As a result, the manufacturer concerned, Sony, had to recall and replace 9.6 million laptop computer batteries in 2006. At the time, this was the world’s biggest recall of consumer electronics. The computer companies involved were Dell, Apple, Toshiba and Lenovo.

But this recall was dwarfed in 2007. According to
The Washington Post
, ‘Nokia offered to replace as many as 46 million cellphone batteries made by Matsushita Electrical Industrial as some may overheat, in what would be the largest voluntary consumer electronics recall. Nokia…said there were about 100 cases of overheating, with no reports of serious injury or damage to property. The affected Nokia-brand BL-5C batteries were made by Matsushita from December 2005 to November 2006.’

Nokia said that ‘the BL-5C batteries…could potentially experience overheating initiated by a short circuit while charging’. Matsushita said that there had been ‘a rare problem in the process of manufacturing battery cells…rather than in the design of the batteries’.

Cell or Mobile?

In Australia, we call them ‘mobile phones’ because they are mobile and we can carry them around with us.

In the USA, they call them ‘cellular phones’ or ‘cell phones’, because mobile phone technology is based on dividing the landscape into little ‘cells’. Inside each ‘cell’, all the cell phones each talk to the same phone tower. If the phone moves to another cell, then there is a ‘handover’ at the boundary, and the next phone tower takes over the job of talking to the phone.

Petrol Station Fire?

So, has a mobile phone ever set off a petrol station fire?

No, according to the Australian Transport Safety Bureau. They looked at 243 petrol station fires worldwide, happening in the 11 years between 1993 and 2004. They did not find a single case.

And no, according to the Australian Mobile Telecommunications Association, who in 2003 said, ‘There is no evidence whatsoever that a mobile phone has ever caused an explosion at a petrol station.’

No, according to the American Petroleum Institute, which notes, ‘We can find no evidence of someone using a cell phone causing any kind of accident, no matter how small, at a gas station anywhere in the world.’

And no again, according to 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 with their considerable skills to make a mobile phone explode a chamber full of petrol vapour, and failed. (Mind you, petrol vapour will explode only when it makes up between 2-8% of the air volume. See also ‘Exploding Car’ chapter, p 187ff.)

To summarise, there has never been a single verified case of a mobile phone, under its normal operating conditions, setting off a petrol station fire.

So Why the Myth?

It is ‘theoretically’ possible to set off a petrol fire with a mobile phone. However, two very special conditions are needed.

First, the phone has to make a spark. Second, the spark has to ignite the petrol vapour. But remember, the petrol vapour has to be in the range of 2-8% by volume—if it’s higher or lower, you can make all the sparks you want, but the petrol vapour will not ignite.

So yes, there is easily enough energy in the battery to make a spark. The amount of energy needed for a spark to ignite petrol vapour is 0.2 millijoules. This is roughly 50 million times smaller than the energy stored in a fully charged phone battery (about 10 kJ).

The problem here for our email myth is that the phone is not designed to make sparks. In fact, part of its design brief is to not make sparks.

There are a few unlikely scenarios that could possibly lead to a spark.

The lithium battery could explode while charging, if its internal regulator circuit was very faulty, and in a very specific way. But you don’t normally simultaneously charge and use your mobile phone while refuelling your car. And having the internal battery regulator circuit fail at the same time is very unlikely.

Second, it’s possible, but very unlikely, that the internal electronics of the phone (not the battery) could fail and make a spark. But this spark from the internal electronics would be much too small to ignite a petrol-air vapour, because all the internal electronics of the phone run at a very low power rating. Another problem in this unlikely scenario is that it would take much longer than a typical refuelling time for the petrol vapour to build up inside the phone to the critical concentration level (of around 2-8% petrol vapour).

Another unlikely scenario is that the battery could fall out of your phone, while it’s jiggling around in your pocket. So assume you would have a loose and fully charged battery in your pocket. But it would be almost impossible for random metal objects in your pocket (e.g. keys, coins, paperclips) to touch the electrical contacts on the battery. This is because the electrical contacts have been designed to stop sparking. They are located slightly lower than the surface of the battery and/or are separated from each other by raised plastic strips.

Anyhow, why worry about the tiny 50 g phone battery when you have bigger batteries in such items as your iPod, CD player and mini-torch? In fact, if you are worried about taking a battery into a petrol station, don’t forget the big 15 kg car battery that powers all the electrics in your car.

Electric Fields?

Okay, so it’s very unlikely for a mobile phone to generate a spark from either its internal electronics or from its battery.

But don’t mobile phones emit an electric field? And don’t electric fields cause the luminous sparks called ‘St Elmo’s Fire’? So can’t the electric field of a mobile phone cause sparks?

Okay, mobile phones do emit electric fields. And yes, St Elmo’s Fire is a strange blue or violet glow, often accompanied by a distinct buzzing or hissing sound, and is a high-temperature plasma. It has been seen by sailors at sea in thunderstorms for thousands of years. But St Elmo’s Fire needs an enormous electric field to generate it—somewhere around 100,000-3,000,000 volts/metre. This is much greater than the pathetic electric field of 2-5 volts/metre generated by a mobile phone with its tiny 3.6 volt battery.

Yes, there are cases where this tiny electric field of 2-5 volts/metre has interfered with heart monitors and infant incubators in
hospitals, and with electronic equipment in aeroplanes. However, the electric field from a mobile phone has never been known to set off a fire in a petrol station. There is not one single case on record.

And consider that, in the UK, about 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. The mobile phone towers have never been implicated in any petrol station fire.

Mobile Phone Tower Hysteria

Mobile phone towers are a cause of much worry – but for no good reason.

The maximum theoretical power that a GSM (Global System for Mobile communications) mobile phone can generate is 2 watts. But because of the way that the phone output is switched on and off, the power is never more than 0.25 watts. And this would be the case only when you are at the maximum possible distance from the mobile phone base station. When you are close to it, the power that your phone generates is a lot less.

But a mobile phone tower generates a lot more power – up to 1,500 watts per frequency channel. So let’s compare a mobile phone tower 50 m away to a mobile phone held only a few centimetres from your head. Measured at your head, the electric and magnetic fields are about 50-100 times smaller from the phone tower than from your phone.

So why do people demonstrate against mobile phone towers? Why don’t they demonstrate against the electric fields from the Sun?