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Oldpilot55
27th May 2008, 02:08
Why don't I earth my car when I fill up with fuel?

IO540
27th May 2008, 07:19
Tradition, most likely.

Also planes do get charged up when flying in rain, and after a landing they may not discharge sufficiently by the time you taxi up at the pump.

But a plane that has been on the ground for hours will not be charged anymore.

Much also depends on how humid the air is. High RH will dissipate static charges fast (in seconds).

I think Gemma all the pipework is conductive. You won't get static in a pipe.

IO540
27th May 2008, 07:34
How does a (assume) nonconductive fluid, flowing through a longer conductive pipe, going to pick up a greater charge?

The longer the pipe, the greater the opportunity for any charge to dissipate into the pipe wall.

My speciality is electronics, BTW, where antistatic handling is the norm.

Lister Noble
27th May 2008, 08:03
Why is it that some cars always have static and others not?
My speciality is retirement ,by the way.
Lister;)

BHenderson
27th May 2008, 08:16
Remember when the new style Mini Cooper came out? There was an early recall because they weren't earthing properly, causing sparks and flash fires.

Bobby

DFC
27th May 2008, 10:04
One does not earth the aircraft during re-fueling. One bonds the aircraft and the refueling instalation / truck so that there is no potential difference between them to cause a discharge.

Who cares if both the aircraft and bowser are at 50,000 V potential (except the person on earth who touches them of course!), provided that they are both at equal potential then there will not be a discharge between them.

That is why the bonding must be in place before caps are removed etc - so that any discharge during the equalising happens before a large amount of vapour is present.

With regard to static build-up on the aircraft / disipation then I recomend that people read up on static wicks etc and also on their tyre manufacturer's literature.

Regards,

DFC

airborne_artist
27th May 2008, 10:36
The tanker delivering the fuel to the petrol station will bond to earth before discharging.

effortless
27th May 2008, 13:09
I got a hell of a whack of a Whirlwind hoist when I were a cadet. :eek: My how we laughed. Or was it a Wessex? Over forty years ago sheesh!

IO540
27th May 2008, 13:52
Who cares if both the aircraft and bowser are at 50,000 V potential (except the person on earth who touches them of course!), provided that they are both at equal potential then there will not be a discharge between them.

except for a corona discharge, into any free air, from any sharp point; 50kV would do that nicely

Gemma, there is no way for a nonconducting fluid to carry relative static charge (that is, one piece of the fluid being charged relative to another piece) once it has made its way through a length of conductive pipe. Do you have any references suggesting otherwise?

AFAICS the whole reason for the earthing strap is to ground the airframe to the ground installation (or the bowser) to prevent a spark jumping across from the nozzle to the fuel tank when the two are brought into proximity.

If the fluid itself could carry a charge, the strap would do nothing and in fact there would be no way to dissipate/equalise that charge.

Mariner9
27th May 2008, 14:08
Gemma, there is no way for a nonconducting fluid to carry relative static charge (that is, one piece of the fluid being charged relative to another piece) once it has made its way through a length of conductive pipe. Do you have any references suggesting otherwise?

In oil tankers, it is assumed that static charge cannot accumulate on product flowing through pipes provided the linear flow rate is <1 metre/second. However, in flow rates in excess of these, you are required to assume that a static charge can accumulate, and take necessary steps to miminise the dangers (generally by inerting the tank)

Static charge is also considered to be present in a cargo until 30 minutes after completion of loading, despite being contained within a steel tank.

Incidently, gasoline is a reasonably good conductor. Distillates (eg diesel and Jet kero) are poor conductors, which is why anti static additives are specified for the distillates but not for spirits.

References can be found in ISGOTT (International Safety Guide for Oil Tankers and Terminals :8)

Them thar hills
27th May 2008, 17:37
Michael Faraday would have been impressed by all this bonding ;)

Zulu Alpha
27th May 2008, 17:47
Perhaps cars should be earthed .... see this

http://www.metacafe.com/watch/42060/car_fuel_fire/

supposed to happen more often with women as they wear more artificial fabrics and wear high heeled no conducting shoes.

My specialty is being special BTW:)

ZA

Mariner9
27th May 2008, 19:46
Gasoline (or indeed Avgas) isn't really a fluid of low conductivity G-Emma; at least not in relation other oils.

You're right that gasolines can still hold a static charge however, and static has caused no end of problems for the oil industry. Certainly good advice re fuel containers.

As I said above, middle distillates have far lower conductivity. Accordingly, ASA's (anti static additives) such as Stadis 450 are routinely added to Jet and in some instances to diesel, despite the fact that the flash point of those products is above ambient temperature. Whereas ASA's are not routinely added to spirits even though their flashpoints are well below ambient (about -40C in the case of gasoline).

Reference: My job as a consultant surveyor and so-called expert :p on the marine shipment of petroleum and petrochemicals :ok: (also numerous industry textbooks, some of which have been authored by myself & my colleagues)

west lakes
27th May 2008, 21:28
Why don't I earth my car when I fill up with fuel?

To put a cynical hat on.
Notwithstanding the technical pros and cons.
On the basis that a lot of motorists don't seem able to understand a number of other safety rules when using service stations (you know the one about not using mobile phones - justified or not it is there, not smoking! OK most don't smoke whilst fueling but I have seen cars with one of the passengers smoking whilst the driver is fuelling), do you think that they would all, without fail, connect the earthing lead - or more importantly remember to disconnect it before driving away!

John Hill
27th May 2008, 21:45
If I recall the study I read correctly it is not the car that gets charged up, it is not the fuel or the fuel pump that gets charged.

According to that study most car filling station static incidents happenend in cold dry weather and at the end of the filling operation. The driver would start the pump then get back into their nice warm car, when the tank was full they would open the door and slide their fat butt in nylon underwear over the vinyl fake leather so charging their body to a nice level. A few steps then when they reached out to the filler handle there would be an equalising arc between them and the car or filler in a vapour rich environment hence the fire.

Windy Militant
27th May 2008, 22:13
I seem to recall the nice man at shell Aviation saying that the filters used on aviation gasoline systems are finer than those used for Mogas this somehow causes an extra imbalance and so a higher potential. Which is another reason to bond the aircraft to balance the system. I'm not sure how this applies to fuelling from jerry cans.:confused:

jb2_86_uk
27th May 2008, 22:16
If I recall the study I read correctly it is not the car that gets charged up, it is not the fuel or the fuel pump that gets charged.

According to that study most car filling station static incidents happenend in cold dry weather and at the end of the filling operation. The driver would start the pump then get back into their nice warm car, when the tank was full they would open the door and slide their fat butt in nylon underwear over the vinyl fake leather so charging their body to a nice level. A few steps then when they reached out to the filler handle there would be an equalising arc between them and the car or filler in a vapour rich environment hence the fire.

Popular Discovery channel show Mythbusters did an episode about this [Series 1, Episode 2: Cell Phone Destruction] and whilst setting out to prove/disprove that mobile phones cause these fires, they also found the above mentioned effect to be (one of?) the main reasons petrol-station fires occur. They actually failed to induce an explosion using a mobile phone.

supposed to happen more often with women as they wear more artificial fabrics and wear high heeled no conducting shoes.

They also did an independant study and found it was women who were more likely to return to the cabin during the process of fuelling - causing the effect as posted by John Hill

Theres another episode JB-ers might be interested in... Series 6, Episode 3: Airplane on a Conveyor Belt.....:ugh:

JB

G-CPTN
27th May 2008, 23:04
According to that study most car filling station static incidents happened in cold dry weather and at the end of the filling operation. The di read river would start the pump then get back into their nice warm car, when the tank was full they would open the door and slide their fat butt in nylon underwear over the vinyl fake leather so charging their body to a nice level. A few steps then when they reached out to the filler handle there would be an equalising arc between them and the car or filler in a vapour rich environment hence the fire.If you watch the video http://www.metacafe.com/watch/42060/car_fuel_fire/
you can see exactly that - the initial flash occurs when the female reaches out to touch the fuel nozzle. (I ran the video several times before I read John Hill's postulation. It seems to fit exactly what is seen in the video.)

radeng
28th May 2008, 08:55
Igniting fuel from a spark requires a certain amount of energy in the spark. If you don't have enough energy, there will be no ignition. There have been a number of papers at conferences about this when considering the use of radio transmitters, although it was many years ago - basically, the subject has been done to death! A lot of the work was done at Sheffield University.. There are also some British Standards on the subject. Because aircraft are much bigger than cars, the energy stored from staitc is bigger:they can also get to a much higher voltage, and the energy stored in the capacitance represented by the aircraft is one half of the capacitance multiplied by the square of the voltage

John Hill
28th May 2008, 09:27
Radio transmissions are an extremely minor risk in the filling station environment. However, radio transmitters and all portable electrical/electronic devices are a real danger if they are dropped on the hard concrete (remember, this is where the explosive vapours lurk) and the knock causes any live electrical circuit to be broken causing a spark.

radeng
28th May 2008, 10:08
>causes any live electrical circuit to be broken causing a spark.<

or even worse, literally catch fire with naked flames comng out!

Arado
28th May 2008, 10:45
Radio transmissions are an extremely minor risk in the filling station environment. However, radio transmitters and all portable electrical/electronic devices are a real danger.....

Like this episode from Brazil, where mis-use of a phone ignites a fuel tanker in a filling station?


www.youtube.com/watch?v=2aW-Qaio6Uw (http://www.youtube.com/watch?v=2aW-Qaio6Uw)

Arado

Flap 5
28th May 2008, 12:44
What they should have is an earthing metal strip sticking up from the ground to touch the car in every refuelling bay. They have it in formula one pit boxes where they refuel and re-tyre formula one cars.