On Sat, 26 Mar 2005 15:58:42 GMT, (Juaquin
Murrieta) wrote:


I just read the thread above on static electricity problems associated
with using jerry cans of various compositions. I have a couple
questions and comments.

First of all, does anyone really know of an accident anywhere? I

I know of several, but they were "way back when" and from metal cans
into metal funnels, with metal screens, into metal tractors. As I
said it was a long time ago as I haven't farmed since 1961

mean, is there anyone out there in this ng who has ever seen a fire
start from a static discharge associated with one of these cans? I
have heard about this for years, but Wal-Mart and hundreds of other
retail outlets sell gas cans that are made of nonconductive plastic.
The red plastic ones I have are not conductive. And...it's obvious if
you have a conductive can, you can get rid of the electrons real easy
by pre-grounding. I'd bet that my red-plastic gas cans are completely
nonconductive however.

I think we should be careful using the word "ground" in this sense.

*Normally* there is only one really important electrical connection.
That is the one between the fuel source and the receptacle. IE the can
and the tank.

We normally refer to this as grounding and although technically not
correct it's as good as any in common usage.

The can, the operator, and the tank need to be electrically connected
together. Normally the true "ground" to earth ground doesn't mean
squat if the source, be it tank, can, or underground storage, is
electrically connected to the tank it is fueling.

The common point *earth* ground is used because it is handy AND it's a
back up means of protection in case the other means of electrical
connection are broken (as in opened)


So, I'm thinking that even if you have a big electron buildup on the
plastic can, it can't flow fast enough to make a spark anyway.

There are some dynamics involved. Yes, gas can flow fast enough out
of a plastic or *metal* container (gas can) to create a spark. It's
surprising how little flow is required if you are really trying to
create one.


I think the older metal cans were more dangerous because they did
conduct and if they were isolated and built up electrons, those
electrons could move fast through the metal spout and make a spark.
Even then, however, I have never heard of a real accident from filling
a tank anywhere. Yes, I've heard rumors of accidents, but does anyone
out there in RAH- land know of a specific accident happening that was
caused by using any fueling can, ever?

Yes, but as I said they were "way back when". No one was seriously
injured except in one case and that was not a fueling accident. It
depends on the concentration of the fumes in the tank and the noise
can be fairly loud, but the two I heard were mover a wwhistling and
very loud, "Fwapppp!".

The main danger is not *normally* the explosion per se, but rather
taking a bath in burning gas which can ruin your whole day.

About a year ago, I saw a video clip on TV where this guy went to
fill a can in the back of his pick-em-up truck and some gas fumes sort
of exploded, burning him quite badly. But, this is the only accident
I've ever heard of or seen first hand and it was something a little
different since it was a spark from a gas pump nozzle somehow.

"Sort of exploded?" Is that something like "just a little bit
pregnant. Not enough to notice, but just enough to make you nervous?"

The gas pump is no different than the can with the exception of the
volume and velocity of the gas coming out. That means it can develop a
charge faster than pouring. In this case the pump was probably
grounded to earth and the truck was not. Had the nozzle been
electrically connected to the truck or can no spark would have
occurred.

Also, it's a matter of the chemical kinetics. Since gasoline is so
volatile the hydrocarbon/oxygen ratio in the air above the liquid
gasoline in one of those cans is too high for combustion. You can
throw a cigarette in a can of gas like that and it will most likely go
out.

Well, kinda, sorta, almost, but not quite. The reason is the
interface between the air and the gas fumes. There are two limits.
The Lower Explosive Limit (LEL) and the upper explosive limit (UEL).
You rarely see UEL used, but LEL is quite common. Some where your
cigarette is going to pass between those limits on the way in.

As an extreme, the LEL for Hydrogen of 4% by volume and I believe the
UEL is 96%. This is about as wide as you are going to get. Gas OTOH
has a much narrower range between the LEL and UEL. I've forgotten the
specific values but they are much narrower than Hydrogen. Still, you
can get a lot of bang out of the proper mixture.

The kinetics for burning are just not right because of the
overload of hydrocarbons. Of course at the mouth of a gas can things
are different. You can have perfect kinetics for burning since the
hydrocarbons are escaping into the atmosphere there is plenty of
oxygen.

This causes a dynamic reaction that creates a "Whooup" (sometimes
accompanied by a bang) sound with the air trying to get in and the gas
trying to get out.


I know that kerosene for instance is much more dangerous because it's
more oily and less volatile. So, you have perfect kinetics for
burning in the air above the liquid in a gas can. We don't put jet
fuel in gas cans for that reason.

I have put a lit "kitchen style" match directly into an open pail of
Kerosene without even a flash. When very close to the surface the
match did get a bit brighter, but there was no flash and the kerosene
put the match out.

I've seen the demonstration done with either the old JP-4 or Jet-A. I
Jet fuel has some additives like Benzene which are much more
flammable.

Anyway, is there anyone out there who knows of a real accident using
either metal or plastic cans?

Been there and seen it, but not at an airplane.
There is an ever present danger of fuel ignition when ever fueling.
Proper fueling techniques should eliminate them.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com


Just curious

----Whaa Keen

"The only difference between a nobleman and a commoner is that the
nobleman thinks one thing and says another."
--Zorro