Jinx,

On Sat, 25 Aug 2007 00:31:38 +1200, Jinx wrote:

> > apparently there have been three fires in petrol stations in the UK
> > that are directly attributable to mobile phones
> 
> I've always been skeptical about that
> 
> http://www.snopes.com/autos/hazards/gasvapor.asp

OK, I was just quoting roughly from a sign in a petrol station near here - looks like they were quoting the mythical Shell email!  Sorry, looks like I was 
led up the garden path...
 
> > who had the phone in his jeans pocket at the time...
> 
> Now how would a pocket fill up with vapour ?

Diffusion through the fabric - denim is a long way from airtight!  :-)

> > I'm mildly surprised that there are no anti-static precautions for
> > fuelling
> 
> That makes a lot more sense than banning cell phones. But you'd
> think the person getting out of the car first might be the one who
> was going to fill it, in which case there would be no vapours yet
> (perhaps some drifting though). 

I know there aren't may people in New Zealand, but surely you are always alone in a petrol station? :-)  My local Saisbury's petrol station has 20 
pumps, and you usually have to wait for a vacant one.  Believe me, there's a lot more vapour around that just your own...

> Some people are sensitive to static
> and get shocks stepping out of vehicles, but I don't know if they
> actually generate a spark

You can see the spark if you're looking at the point of contact at the time - easiest (and painless!) way is to hold a key firmly and use that to make 
the contact.  I don't know if the shock you feel is due to the high temperature, or the high voltage-density at the point of contact, but by making a 
piece of metal "feel" the spark, you don't.  I always do that if I suspect I'm carrying static - use a coin or a key to discharge myself to whatever is 
earthed.

> What about hot exhausts, engines running as you pass someone
> filling up, even scuffing a bit of gravel and making a spark ?

OK: exhausts are nowhere near hot enough to ignite petrol.  Even glowing red-hot I don't think they'd manage it.  Engines running don't have exposed 
sparks (it's supposed to be an *internal* combustion engine! :-).  To get a spark from gravel you'd have to have flint in it (unusual, to say the least) 
and scuff it with something metal.  This *could* create a spark (ask the inventor of the flintlock) but I don't know if it's ever happened, and I don't 
remember seeing gravel on any petrol station forecourts.  In fact I'm sure it wouldn't be allowed, as any spillage could be lurking in there, waiting to 
ignite, rather than running away and/or evaporating.

> How far do you go to ban every possibility ?

I think you minimise the possibilities - don't allow anything that could cause ignition.  Petrol station fires *do* happen, and I just hope I'm never 
around when one does!  (I worked in one when I was a student - up until then I liked the smell of petrol, but not any more! :-)  On my last trip to 
New York I noticed that all of the petrol pumps now have fire-extinguiser jets above them, pointing down and outwards.  I think this must be a new 
regulation, because I never noticed them before, and a lot of them seem to be newly-installed.

Cheers,


Howard Winter
St.Albans, England


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