Tuesday, 7 September 2010

Blowing up gas stations with cell phones; if only killing stupid people was that easy

Last week one of the many walking parodies of bureaucratic ineptitude which clutter up my life circulated an email to everyone in his address book warning us all that if we used our mobile phones at petrol stations, we ran the risk of annihilating the entire world through the evil of cell phone sparks igniting the insanely volatile fluid we routinely fill cars with.

I deleted the email immediately rather than have it sitting on the screen tempting me to hit reply all and say something which would only get me into pointless arguments with buffoons in suits. I'm annoyed to discover that I'm still brooding on the idea that there's no law against putting technology in the hands of people so pestilentially stupid that they can actually believe that cellphones can transform petrol stations into fireballs.

The idea has long since been thoroughly debunked. Mythbusters took it down in their very first season. In the UK, Brainiac, a show dedicated to making EVERYthing explode, concluded that the only way you can get a cellphone to cause an explosion is to replace the phone with a stick of dynamite with the word Nokia written on it.If TV doesn't float your boat, snopes.com blew the story out of the water:- http://www.snopes.com/autos/hazards/static.asp


Even if the assembled might of TV and websites don't persuade you, lets just think about the numbers for a moment.

There are 330 million people living in the US, with 1.15 cellphones for every inhabitant and 245 million cars and SUVs between them. It seems safe to suggest that at the very least, there are a billion instances of people filling their petrol tanks a year in the US, and that in the overwhelming majority of those instances, there's at least one cellphone present. That's assuming that each car is only filled up four times a year, which I think you'll agree is a very conservative assumption. So even if the odds against a phone igniting a petrol station were a billion to one, there should be one incident a year. Yet, there has never been a reported incident. Not once in the fifteen years since cell phones began to get common and then ubiquitous has there been a confirmed incident in which a cellphone lit up a petrol station.

Now that's just anecdotes meeting data; just because something has never been reported doesn't mean that it's never happened or that it's impossible. But the fact that in ten years there's never been a confirmed incident anywhere in the world suggests that you're significantly more likely to win the lottery than create a Michael Bay scene at your local BP station. In fact, you're significantly more likely to win the lottery, even if you haven't actually played it.

But it's better than that, because it's comparatively straightforward to prove with actual scientific deduction that it's vanishingly improbable that you could detonate petrol with a cell phone. A cell phone operates with milliwatts of power from a battery rated in the ballpark between 500 and 2000 mAH. A car battery, even a tiny one, has 40 AH. The smallest conceivable car battery has twenty times the power of the largest possible cell phone battery. Hold on to that thought. It gets better. The operating voltage in a cellphone is between 3 and 5 volts. The operating voltage in a spark plug is a minimum of 12,000 volts. It takes quite a lot of electrical judo to get the power out of a 12 volt car battery and through a spark gap at a minimum of 1,000 times the rated output voltage of the battery. And car manufacturers don't go to all that trouble because it's fun, cheap, or cool. They do it because it's the only way to be confident that the spark will ignite the petrol in the cylinder every time.

Which brings me to the contents of the cylinder. Immense ingenuity goes into ensuring that each cylinder in the engine is filled with a precisely measured mixture of petrol and air so as to get the maximum explodiness out of the petrol each time the spark plug fires.

So, to go back over this again; the most common kind of ignition of petrol fumes in air requires a precise mixture of petrol vapour and air in a confined space and a minimum of 12,000 volts. 12,000 volts. Cell phone voltage - 3 to 5, depending on the phone. Spark plug; big open spark gap hanging right in the middle of the petrol-air mix. Cell phone - let's keep this simple; have you EVER seen anything in your cellphone emit a visible spark? No, you haven't. The entire device is sealed in plastic, with every single electric component carefully screened away from your sweaty hands because the electronics are so subtle and complex that your sweat could interfere with the working of the machine.

If cellphones could make petrol explode at petrol pumps, the car manufacturers of the world would be replacing the electrical systems of cars everywhere with cell phones. They're not. So the next time someone sends you that email alerting you that you could turn your local Maxol into a Michael Bay cut scene by taking a phone call - well, it's up to you what you do. But if enough of us can keep quiet while stupid people get to shout from the rooftops, soon the only thing we'll be able to hear is stupid.

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