You need three things to ignite gasoline vapor.
(1) Air (i.e., oxygen), (2) proper air/fuel vapor
ratio, and (3) a spark.
The spark needed for ignition isn't much, less
than 1 milliJoule in the right conditions, and on
the order of what's produced by static shocks we
experience. But for fuel flowing in fuel lines, I
doubt you can generate that at the relative
snail's pace of fuel flow there, plus it has to
arc somehow too. And you have or little or no
air, and if you did, the air/fuel mixture's too
rich.
Static can also be generated in nonconductive
filler tubes and plastic tanks, but I've seen it
stated, although not in an authoritative source,
that the fuel there is always way too rich to be a
problem. Consider what a "flooded" gasoline
engine is, namely one with some liquid fuel in the
induction system and/or cylinders. But it won't
start, and that's with compression of the
air/fuel, and the ignition system's spark is many
times the minimum energy needed. So the reasoning
goes, with gobs of wet fuel in the filler tube and
tank, no spark short of massive, will do
anything. This then argues that once you're past
the filler neck, you're home free.
This is consistent with the general advice, here
and elsewhere, to use metal containers, and
short-circuit the filler neck and source
container, directly, and additionally thru common
earth ground if the source tank is not grounded.
It is interesting to note that Chevron can cite
only 25 reported fires in 6 years in the U.S., and
mostly involving pickups with bedliners. Consider
the tens of millions of times annually that
people, often not following their advice -- watch
'em some time, fill plastic containers, or boats
or ATV's with plastic fuel tanks and insulated on
trailers, etc., etc. A fueling fire appears to be
a very rare event, even with unsafe fueling
practices, and should logically approach zero
probability if done properly.
Regards,
Fred Fillinger, A063
JohnJMoran@aol.com wrote (in part):
>
> Apparently, Europa recognized the static discharge possibility and took steps
> to avoid it by using conductive hose. Unfortunately, US fuel contains
> various chemicals which reportedly attack the small bore hose supplied,
> causing it to deteriorate more quickly than desired. In an attempt to avoid
> this deterioration, I replaced much of the small bore hose with hose from the
> auto store but after reading of the static problem noted above found that
> this auto hose was non-conductive. Thus, in attempting to avoid one problem
> I introduced another.
> (snip)
> Of course, there is always a question remaining: should a section of safety
> wire be added such that it extends from the filler fitting down inside the
> filler pipe or is this superfluous due to a low breakdown voltage of the
> interior insulating layer in the filler hose?
>
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