We got an e-mail message the other week at work warning about the dangers of mobile phones causing fires or explosions at the petrol station when you are filling up. The message said that this can even happen if the phone is in your pocket or in your car! I’m pretty skeptical about this, has anyone heard of this actually happening?
http://www.snopes.com/autos/hazards/gasvapor.htm
The ringer in modern cell phones is electronic, not mechanical. No spark is generated. It is more dangerous to turn your radio on & off while fueling; at least there you are creating a small arc across the switch contacts when you make & break them.
The car itself, however, is an excellent source of ignition energy. The ignition coil can generate a 20 to 40KV or more potential when you start your car, so I suggest you turn off the ignition at least a block away from the station and push the car in. Then push it at least a block away before starting it again. Those pesky petrol fumes are all over the place 
I should add that the current popular theory blames some small bursts of flame on static discharge from any object, not just cell phones. I don’t know how much solid data has been collected to support this, or if it’s just another paranoid neurosis.
http://www.snopes.com/autos/hazards/static.htm
And see this recent thread on preventing static buildup/discharge:
I personally have been shocked while talking on a 2.4 Ghz phone while tinkering with an 802.11b wireless access point (boosting the signal). I can’ t explain why it happened, I just know it did. And I wasn’t touching any wires at the time.
we’ve discussed this just recently…
http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=126221
As far as I was aware, nobody was claiming that the ringer was the problem; I thought the claim was that the microwave emissions could ignite petroleum vapours or that the antenna could cause a spark if the insulation was damaged.
(NB: I’m not going to argue in support of these claims)
IMHO, the most likely scenario is that dropping the phone on the ground can short out the battery and cause it to get hot and catch fire pretty quickly.
Also, I don’t mind all these rules so much at petrol/gas stations–everybody seems to forget that gasoline burns very easily and is essentially a dangerous chemical, but since you don’t experience the fire part first hand, most people don’t think there’s any danger.
Anyway, by banning smoking and open flame at the pumps, most of the problem goes away. The trouble is that a gas station fire is very very bad and relatively easy to start, so although the risk of a cell phone causing a fire is low, the possible damage is large, so the “probabilistic damage” is somewhere in the middle.
My only complaint at the pumps is that they have a big sign warning you about cell phones, which haven’t yet caused any pump fires that I’m aware of, and no signs at all warning about static discharge, which has caused maybe a hundred fires (about a hundred out of millions of people going to the pumps, if you want to keep this in perspective). It’s a classic case of people misjudging risks if you ask me.
To put it in perspective, I know of a couple of incidents where cars were damaged by falling meteors. Since falling meteors cause more damage than cell phones, WHERE ARE ALL OF THE BEWARE FALLING METEOR STICKERS???
The signs are probably a knee-jerk reaction to a hyped bit of (pseudo)science, but from the point of view of the garage owners, it’s a small risk upon which it is easy to take action, meteor strikes and static discharge, whilst they may be more likely to happen, are more difficult to control (do you insist that nobody charge their tanks while wearing trousers of synthetic material?).
There’s no logical reason why a small, easily controlled risk should be ignored just because a larger risk is being ignored.
Since this topic has been discussed so recently, I’ll close this thread and direct further comment to the earlier thread, linked to above by xash