grounding the fuel filler tube

[Eneto-55]

I just read an article over on Hemmings about rewiring, and one thing mentioned was adding a ground from the upper filler tube down to the tube that is a part of the gasoline tank.  The author was working on a fiberglass bodied car, so the upper filler tube was not grounded.  Well, it isn't on our cars, either, because it goes through a rubber grommet at the fender, and is connected to the tank tube with a piece of rubber hose.  

 

So, has anyone ever heard of an electrostatic spark setting off a blaze at the gas tank filler?  Or can you even get a spark there, since that tube is isolated from the rest of the car?  Would adding a wire from the upper tube down to the lower tube (as that author did) actually make it worse (i.e., more likely to have an electrostatic spark there)?

[Sam Buchanan]

This is a point of concern in the aviation world but not sure if it applies in a practical sense to our vehicles.

 

I don't play an electrical engineer on TV but as I understand the matter, the likelihood of a static spark is enhanced when the fuel filler nozzle has a different electrical potential from the fuel tank. This occurs in aviation because the high speed of the airframe (friction) through the atmosphere can result in an electrical potential building on the airframe much the same as when rain falls through a cloud (lightning). The aircraft pulls up the fuel station carrying its potential which is different from the potential on the truck...when the fuel nozzle touches the airframe.....pow! This is prevented by the strict use of a grounding cable which is connected to both the fuel station and airframe BEFORE fueling and this dissipates any difference of potential charge. A potential charge can also result from the flow of fuel through the nozzle and air as it enters the fuel tank if both are not properly grounded.

 

We see a similar situation at our auto gas pumps. Ever seen the placard on the pump that states you must put your plastic lawnmower gas can on the ground before filling it? This is to assure the can has the same potential as the pump....leaving the can in the bed of your rubber tire insulated truck bed is considered bad practice.

 

Will an explosion occur if these standards aren't practiced? Most of the time....no...conditions need to be in a small window to support combustion (low humidity so the spark occurs). But it only takes one spark to create a fiasco. I think the carbon in our car tires is considered to have enough conductivity to drain potential differences to ground so we don't worry about filling up the tank. But having the filler neck electrically bonded to the auto frame is not a bad idea.

 

I stand ready to be further educated on this matter. 

Edited March 17, 2022 by Sam Buchanan

[desoto1939]

If I remember correctly the filler neck on our cars is not steel it is some alloy or made with a non spark metal. So there is a mnior aspect of creating a spark. If there ever was an issue of this happening it would have happened a long time ago and someone would have chnaged the metal fuel filler tube.

 

I have persoanally seen the issue with the plastic gas can creating a spark in the plastic bed iner on a pickup truck.  It is not a pretty site and you run like a bat out of hell when you see it happen.  Also i think the nossle end on the gas pump is also made of a none conductive material but with the pastic gas can and the statis electricity from the plastic bed liner this is where you have the issue becsue the fumes are what ignite.

 

Rich Hartung

[Eneto-55]

When we were in Brazil, and flying regularly out to the village by Cessna 206, the pilots NEVER used a plastic gasoline container, always a steel can.  They said that the fuel passing through the plastic nozzle could create static, and therefore a spark.

 

About the filler tube on the cars:  Mine was rusted, so I bead blasted it and cadmium plated it.  It sure looked like steel after I blasted it.  I guess I could check it with a magnet, but what other type of metal could it be that wouldn't be conductive?  Some kind of bimetal?  

 

This reminds me of a story my dad told us from when he was in elementary & middle school.  He was born in 1930, so this would have been the late 30's into the 40's.  He attended school at a one-room school in rural western Oklahoma, and the students all either walked to school, rode horses, or drove old clunkers.  Anyway, the guys with the cars would park side by side, and open their car doors so that each car grounded to the next, on down the line.  The first one had one spark plug wire touching the car someplace.  The guy at the other end called one of the young students over, and would reach out & touch their ear.  The way I understood, the spark passed through each car, and gave the kid a jolt on the ear.

 

My brother had a repair shop in Nebraska, and my younger brother & I went up there for a couple of months to help him out, to get caught up on work.  He was working on a car he had towed in.  The owner had assured him that he hadn't tried to start the car with ether.  It wasn't starting for my brother, either, and he decided to pull the distributor.  He forgot that he had left the key on, and when the distributor touched the side of the hole, BANG!  All that fuel & ether that had run down into the crankcase exploded.  My other brother & I were outside, stripping wrecked cars.  We ran in, thinking he had blown himself up somehow.  He couldn't hear out of one ear for a couple of weeks.  The blast blew the oil breather cap off of the one side (it was a V8), and the valve cover on the other side was ballooned and torn almost loose from the head.  (Sorry, here I am "post-bombing" my own thread - getting way off topic.)

[Sniper]

Brass is used for striking tool in a potentially explosive environment.  Not sure how it would play in a static electricity scenario though.  If it bother's anyone, a hose clamp on each tube and a wire between them will ground it out.  Though I will point out that the factory never really saw fit to do that so I am not sure it's an issue, nor am I sure that adding the jumper setup I mentioned would NOT be an issue either.

 

I do know the factory put a jumper across the fuel hardline to the sending unit nipple on my 65 Cuda, but that was to ensure the sender had a good ground.  The filler tube had a rubber seal where it entered the tank, but I believe the other end was screwed tot eh body at the filler cap.

[Sam Buchanan]

2 hours ago, desoto1939 said:

I have persoanally seen the issue with the plastic gas can creating a spark in the plastic bed iner on a pickup truck.  It is not a pretty site and you run like a bat out of hell when you see it happen.  Also i think the nossle end on the gas pump is also made of a none conductive material but with the pastic gas can and the statis electricity from the plastic bed liner this is where you have the issue becsue the fumes are what ignite.

 

Rich Hartung

 

Pretty sure the fuel nozzle is metallic (every one I recall seeing anyway) and the hose also has a conductor in it. This is so unbalanced potential will be neutralized when the nozzle touches the metallic filler neck before fuel begins flowing. I wouldn't be surprised if the proper hoses for our filler necks have some degree of conductivity.

 

From what I've seen this is the difference between fuel transfer pumps (farm equipment) that are designed for gasoline vs some other liquid. The gasoline hoses and pumps are conductive which is more expensive than the non-conductive hoses and pumps used for petroleum products.

Edited March 17, 2022 by Sam Buchanan

[Eneto-55]

8 hours ago, Sam Buchanan said:

 

Pretty sure the fuel nozzle is metallic (every one I recall seeing anyway) and the hose also has a conductor in it. This is so unbalanced potential will be neutralized when the nozzle touches the metallic filler neck before fuel begins flowing. I wouldn't be surprised if the proper hoses for our filler necks have some degree of conductivity.

 

From what I've seen this is the difference between fuel transfer pumps (farm equipment) that are designed for gasoline vs some other liquid. The gasoline hoses and pumps are conductive which is more expensive than the non-conductive hoses and pumps used for petroleum products.

I have never heard about conductive rubber hose, so I would not have thought that I need to replace the filler neck hose with a specially designated type of hose.  There is no way to reuse the original from my 46.  It is really hard, and would not seal, even if I could force it back onto the two tubes.  I do still have it, and I will examine it, to see if I can see any copper or other conductive strands in the inside surface, and maybe do a conductivity test. 

 

Thanks to all who have responded - This is all very interesting, and potentially very important. (And all new to me.)

[Sniper]

There is a specific filler hose out there, SAE specification 30R6 applies, but I will be darned if I can find an actual copy of the specification or any mention of conductivity.  It may have carbon in the blend and that would be conductive, but I can find nothing mentioning that.

 

Closest to finding out the specifications, no mention of conductivity though, is in this thread.  I would go for an ethanol resistant one if you can find it.

 

http://forums.pelicanparts.com/porsche-911-technical-forum/671288-sae30r6-kx-fuel-line.html

[Sam Buchanan]

38 minutes ago, Eneto-55 said:

I have never heard about conductive rubber hose, so I would not have thought that I need to replace the filler neck hose with a specially designated type of hose.  There is no way to reuse the original from my 46.  It is really hard, and would not seal, even if I could force it back onto the two tubes.  I do still have it, and I will examine it, to see if I can see any copper or other conductive strands in the inside surface, and maybe do a conductivity test. 

 

Thanks to all who have responded - This is all very interesting, and potentially very important. (And all new to me.)

 

This is just a guess on my part, but I suspect if the hose has some degree of conductivity it is due to the carbon composition, not an active conductor such as copper. It wouldn't take much conductivity to drain a static charge to achieve neutral potential. But I have no idea if such a hose is available. My go-to site for out-of-the-ordinary materials is McMaster-Carr and they list a hose that is conductive due to its carbon composition:

 

https://www.mcmaster.com/hose/hose-and-hose-fittings/static-dissipative-high-pressure-braided-chemical-hose/

 

But that hose doesn't have any application for us. Interesting topic, maybe we got a charge out of discussing it.  ?

[JerseyHarold]

I replaced the rubber section of the fuel filler hose in my '52 Cambridge with a Gates product that had a metal strip molded into it.   Maybe it was there for grounding purposes.

[Sam Buchanan]

2 minutes ago, JerseyHarold said:

I replaced the rubber section of the fuel filler hose in my '52 Cambridge with a Gates product that had a metal strip molded into it.   Maybe it was there for grounding purposes.

I think that is a valid assumption. Have a part number and source?

[JerseyHarold]

1 minute ago, Sam Buchanan said:

I think that is a valid assumption. Have a part number and source?

I replaced the hose back in the '90's and don't have the part number anymore.  The Gates catalog had a separate section for this type of hose and listed various diameters.  I bought mine at an auto parts store and they sold me a section from a bulk roll.

[desoto1939]

I just contacted Tanks Inc and they informed me that all of their filler neck are steel. i discussed the above issue with their tech support person and he informed me that all gas pump handles have a plastic (rubber) handle to prevent the issue of creating a spark when filling our cars or trucks.

 

So they fell that this is not an issue.  The real issue is of the Plastic gas container residing in the back of the pickup truck that has the plastic liner. This creates the static charge.

 

Rich Hartung

Desoto1939@aol.com

[Eneto-55]

I should ask one of our jungle pilots, so that I can be sure I remember correctly, regarding what I said earlier about the plastic nozzle on a gasoline container.  But I'm wondering how many of us will occasionally put gas in the car from a container, not at the gas pump.  I know that Av gas is more combustible than automotive gasoline (used it in a moped I had down in Brazil, and man would it go), but figure I will still take precautions, because while it may be a sort of waste of time, I have occasionally bought gas in a 15 gallon barrel, because the price was good at the time.  Then later transferred it into my daily driver.  So maybe I've been doing dangerous stuff here.  (You aren't even allowed to do what we did when I was a kid - we always bought mower gas in a glass jug.  For some reason they don't much approve of that anymore.)

[Sam Buchanan]

The reason why the aviation community frowns on fueling from plastic cans is the nozzle isn't conductive so a difference in potential between the can and airframe isn't reduced and a static discharge can ignite the fumes. However, I have burned a lot of auto gas in some of my lighter aircraft but the precaution I take is always using a Mr. Funnel. This funnel in addition to having a filter that water will not pass through is conductive and allows the can to safely achieve the same potential as the fuel tank.

 

 

Another thing I've done when using a transfer pump is use a ground cable. A clip on one end of a 1/16" cable is attached to the exhaust stack of the airplane, the other end is attached to a length of stainless welding rod which is dropped into the can. Is all this necessary? Don't know...but so far no fires.

Edited March 18, 2022 by Sam Buchanan