Static Electricity

TodFitch · February 21, 2007, 10:46:37 AM

As one fills the tank the "empty" space above the liquid fuel is purged and comes out the filler opening. That "empty space" is a saturated mixture of gasoline vapor and air. I would imagine that the mixture is too rich to easily ignite in the tank but as it dissipates into the atmosphere near the filler cap there would have to be an area near the filler where the mixture is just right for easy ignition.

So I wonder: In places like the Los Angeles basin and the San Francisco Bay area all gasoline stations are equipped with vapor recovery devices. If you don't have them where you live, basically there are two hoses (newer designs have a concentric design with the larger vapor return surrounding the fill hose) and a rubber boot that is supposed to seal the filler area. The second hose is to take the fumes away and extract/store them somewhere. I have always wondered how well they worked in keeping unburned hydrocarbons out of the air. I have also wondered if there was enough gasoline recovered that the station owner could do any thing with it. Now I wonder if the removal of gasoline vapor would have an effect on static spark initiated pump fires.

Does anyone know if the gas stations that are equipped for vapor recovery have a lower rate of fires than those that don't?

Wm Steed · February 21, 2007, 09:27:06 AM

Richard's last posting to this thread was really good, well worth the ten minute viewing time.

I would venture the guess that the reason why females have the highest incident of fueling fires (78% per the film) is because of the higher percentage of man-made fibers their cloths generally have. Man-made fibers seem to creat an electrical charge quicker than natural fibers such as cotton and wool, remember the TV commercials showing STATIC CLING, it is always a womens skirt/dress that is all clingy and puckered up. ;D ...Bill

Richard Dryman · February 20, 2007, 06:22:42 PM

safety video: http://youtube.com/watch?v=nAA5w8PLs-0

Guess this should end the whole thread.

JimCno · February 19, 2007, 06:41:43 PM

Oh, it happens in this country too. I once saw a news report about pump fires started by static charges and they said that most of them were caused by women (something about the clothes they wear) who put the nozzle in the car then went back inside the car to get something and built up a charge by sliding across the seat, just like the video. They recommended not getting back in the car once you start pumping gas.

I also agree that the girl in the video looks like she could be building up quite a charge with all the figiting she is doing with her sweater.

Wm Steed · February 19, 2007, 01:21:47 PM

I noted when I looked at the clip of the gas station fire that the captions were mostly in spanish... This would led me to believe that the insident was filmed in Mexico and/or south America. With the lax building codes in either of these areas I would venture the guess that something could be, or is amiss with the contruction of the station. There is also the possibility that the whole thing was staged, why I have no clue ??? , I guess I am just a doubting Thomas when it comes to things that are on video. For many years I have been an expert in construction defect litigation, the contractors version of malpractice. I have never been envolved in a case where video pictures of a problem area was allowed in the court room, the reason being that video is to easy to manipulate. I have always found it to be interesting that civil and/or chriminal cases allow the video recorded evidence.

Back to the static issue..... My neighbors son was a Avoniac (spl?) tec in the U.S. Marines for five years. At differnent time he encountered a problem with the avoniac's on helicopters from what appeared to be electronic interferance. The problem was worse when they deployed the aircraft to sea duty flying off of carriers. Mel thought the problem might be static electricity, the tec- reps for the air craft manufacture did not think so. Mel called me, then his Dad who had been a tec for Zerox for thirty-six years. We both told him it was static electricity and to attach a ground strap to the air craft anytime it was aboard ship..... Wha- la...... problem solved.....Mel got a nice accomodation from the Marines and the manufactures tec-reps learned something. Funny how something so simple could be overlooked in this high tec age we live in....Bill

FourDoor · February 19, 2007, 11:31:51 AM

I've watched it several times and I think it's the girl producing static electricity from moving her clothes around,and rubbing her backside on the car seat, and she discharges to the pump handle and car fender when she touches them. An object does not have to be grounded for it to accept a charge. It's called the 'capacitive effect'. Even though there is no metal path through a capacitor it charges up one of it's 2 plates/foils because of this 'effect'. Right now I touch the metal door frame on my cars BEFORE I get out because if I don't I get a nasty shock as I discharge into the car body when I turn around to close the door even though I'm wearing rubber winter boots and the car is not grounded. I think it's the same set of circumstances that set off the fire when the girl touched the fender/gas nozzle. We grounded everything whether the aircraft had flown in the last few minutes or the last few days. I think the Canadian Armed Forces knows what they're doing.

Richard Dryman · February 18, 2007, 07:19:38 PM

Not sure this is not here but it sure open your eyes about static electricity when you put gas in your gas tank. Watch what happen when the girl slides across the seat then comes back to take the hose out of the filler neck !!!!!

http://youtube.com/watch?v=7KK48hQ78Kk

Bill Ward · February 18, 2007, 02:50:18 PM

Thanks a bunch guys!

Maybe that will be enlighten my website visitor.

And now I'm just a wee bit more informed myself.

Bill Ward
:-[

Wm Steed · February 18, 2007, 01:06:50 PM

JimCno did a very good job of explaning static electricity from a more technical side. I think static electricity is one of those smoke and mirrow things that most people just do not understand. How many of you remember the clear plastic seat covers that were so popular in the 1950's. People sliding across them built up so much static electricity within their bodies that when they exited the vehicle, the minute they touched something that was grounded they got zapped....The answer was to attach a ground strap which hung under the car, touching the ground (earth) to bleed off the static electricity. In the early 1960's the "BONDING" of a vehicle chassis became very common. The manufactures started to put small braided ground cables onto all portions of the body, hood to cowl, fenders to body, engine to body, engine to frame, body to frame etc.. This tied everything together bleeding all of the static electricall charge back to the source, gen/batt/alt. The "Bonding" of the body eliminated the problems that were arising with static electricity generated by vehicles interferring with TV and FM radio tranmission..

Many years ago the company I owned did a lot of work on new gas stations, if memory serves me right the fuel hose is grounded via a wire leading from the nozel back into the dispensor. The nomal amount of static electricity builtup in a car is so minor it is bled off without anyone ever knowing it was there.

I learned a neat little trick many years ago from a fellow I knew. He had somehow figured/found out that dust has an electric charge (positive) from passing through the air. He also theorized that a vehicle was electrically charged after all the sanding and prep work was done prior to painting. To minimize the dust, ect., from entering the new paint he hooked a ground wire to the vehicle and to a good ground source. The ground wire drained off the static charge which in turn repells the dust particles. Try it next time you paint a car, you will be amazed with the results....Bill

JimCno · February 18, 2007, 10:26:10 AM

You guys have already said it all. I'm just throwing my two cents in because I am an electrician. As said before, ground is ground. On your gas pump, it is grounded, end of story not positive, not negative, just grounded as in no voltage between it and ground. You do that by driving a ground rod into the ground and running a wire from that to every metal part that is not supposed to carry current.

Ground on a car is not a true ground, that is to say it is not at ground potential because their is nothing referencing it to ground. No ground rod, no chains dragging on the ground, it is not really a ground. It is more accurately described as a "Common Ground". That means one side of the battery is connected to the metal body of the vehicle and thus becomes part of the conductor. That way you only have to run one wire to a device and the return path can be run to the nearest body piece. It makes no difference to the electrons which side you ground.

Static electricity is not caused by the battery. It is caused by friction and induction. Friction is the same action as rubbing a glass rod with a wool pad or walking barefoot across certain carpets, especially in winter. Induction would be like driving close to high power wires and building up a charge. Neither of these have anything to do with 6 volt or 12 volt or positive ground or negative ground. It has to do with the air being dry and you wearing wool socks or some other piece of clothing that would build up a charge.

Airplanes can build up a charge by traveling through the air but I wouldn't think cars can go fast enough to build up a charge. From all the reports I have seen on gas pump fires starting from a static charge, it had to do with the clothing someone was wearing , not from the car. If static on a car was a problem, we would have to attach a ground wire to our car before filling up just like the previous post mentioned for airplanes.

FourDoor · February 18, 2007, 12:07:50 AM

The 6/12 volt theory is ,as said,hog wash. The only thing I might add is that static electricty does build up on isolated vehicles that are up on rubber tires. In the Canadian Forces (Air Command) I was 'certified' to refuel aircraft on the flight line. This consisted of first grounding the fuel bowser (tanker) to a ring in the concrete apron that was connected to a copper pipe going deep into the earth. Then another ground line ,which had a plug on the end of it, was unreeled from the bowser and plugged into a socket on the aircraft. This dumped any static electricity and also kept the aircraft and the bowser at the same potential as the fuel was transferred. The airman could be put on charge if the procedure was not followed. The problem of static electricity was most noticable on cold dry winter nights for some reason. I've actually seen the arc when the plug touched the aircraft. Maybe something along these lines is what is 'going to blow everybody up', but it has nothing to do with battery voltage.

Wm Steed · February 17, 2007, 11:32:50 PM

I am not an expert either on electricity, I was very deeply involved in electronics when I was in the service and did graduate from a very good school ran by Philco for the U.S. Army. So..... to the theory that 6v positive ground will cause a fuel dispensor to blow-up any faster or more often than a 12v negative ground, I say HOG WASH!!!!
True.... fuel dispensors have signs on them cautioning people to not use their cell phones while fueling up a vehicle, but tell me..... when was the last time you picked up your local news paper and/or saw an announcement on prime time news that a service station had blown up because of a cell phone or a 6v positive ground vehicle??

Most people are most likely not aware that all phone systems are positive ground and that the current is flowing through the wires all the time only being interupted when the phone is hung up, thereby braking the connection by interupting the negative hot wire. Actually there are several systems in a vehicle that work the same way, they are "hot" all the time just the ground is interupted.... courtesy lights is usually one. Most high end Motor Homes use 6v batterys in a series, positive to negative, mine has six of them, the final result is 12v from the 6v batteries which is fed through a thing called an inverter, coming out 110v.....Kind of spooky huh :-\

When I hear statements that have very little substance it brings to mind an article I read many years ago. The article was published in the early 1900's by a fellow that was warning people about the medical hazards of electriifying homes because of the radio waves the electrical current would transmit through out the building, thereby exposing the occupants to possible brain damage. Every once in awhile this hype resurfaces when the fruit cakes oppose a new power generating plant....Bill

12905 · February 17, 2007, 11:23:50 PM

I'm no electrrical engineer, but I think the comments about dangers of fueling a positive ground system are hogwash. First of all, the vehicle is isolated from the global "ground", so its electrical system, regardless of voltage or polarity, is isolated from its surroundings. Also, as the metal parts of the vehicle constitute ground for its on-board system, there is no difference of potential between the car body/frame and any part of the surrounding "ground".

I have never taken a gasoline filler hose apart, but I am sure that the metal nozzle, a conductor, is isolated from the rest of the pump unit through the hose which is a dielectric, so no current flow is possible to or from the nozzle and the pump.

In addition, what I remember from theory lessons in the distand past is that the decision to move from positive ground to negative ground was based on the move from 'current flow' theory (negative to positive) to 'electron theory' (electrons move from positive to negative). I still have a hard time figuring out which 'hand' rule to use with which theory to determine the north pole of an electromagnet.

TodFitch · February 17, 2007, 10:47:43 PM

I wonder where the "negative ground gas pumps" came from. Ground is ground, especially in a system that contains components buried in the earth. No positive or negative about the pump.

So the question is what is the electrical potential of your car chassis (and thus gas tank) relative to the nozzle of the filler hose at the gas station. And the polarity of the battery attachment to the electrical system in your car has nothing to do with that.

If it were a problem, every positive ground car would have blow up decades ago within the first few times someone tried to put gas in them.

Bill Ward · February 17, 2007, 06:09:39 PM

OK Guys,

Here's one that I don't have a clue about.? As you know, I run a website www.oldplymouths.com in which I try to tell folks that I am not an expert - but I still get questions way above my level of non-expertise.? The latest of many to stump me is about 6v vs 12v systems and static electricity.?

I will quote the fellows comments:

...."the danger of having a 6V positive ground system when refueling your gas tank.? Negative ground gas pumps and 12V negative ground systems ... can... create fires due to static electricity ..... I don't know how much of a concern it is, but, a 6V positive ground system is higher in electrical potential than the negatively grounded gas pump."

An interesting question?? Any of you electrical gurus care to weigh in??

Bill Ward
???