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What Electrostatic Discharge (ESD) protections exist in the gas pumps at gas stations? I believe that here more than ever even one spark is intolerable. How can a it be assured that there is never any potential difference between a car and the gas pump that would cause voltage to arc from the gas tank to the pump when inserting the hose?

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    \$\begingroup\$ It helps when the pump is not located in or near a Hollywood film set. \$\endgroup\$
    – jippie
    Commented Oct 9, 2012 at 19:23

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Basically it's because everything is static dissipative. i.e. conductive, but not highly so, but sufficient to ensure that any charge gets bled off. Even the concrete being poured is slightly conductive.

This reminds me of a homework question in EM theory that talks about the need to have ground clamps on aircraft whilst pumping fuel because of the charge build up from fuel in the hose being ionized (from gamma rays etc.) on the way to the plane and thus pumping charge into the plane. When the nozzle is removed you get a spark.

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photos here In fact, they do spark and explode!

A sign that tells you how to to behave is the only obvious protection I can see, though maybe there's hidden stuff behind the scenes. Personally, I think some sort of affordance that forces users to touch a grounded piece of metal before pumping would help a bunch. In the olden days, we'd always have to flip some form of mechanical lever to enable the pump and reset the price tally from the person who pumped before us, so this is probably doable.

I think a flame detector in the pump handle that cut off the gas flow might prove useful, too. The really bad accidents occur when the fumes flash over and somebody panics and removes the still-pumping handle.

At many of the gas stations I've used, they remove the clip that keeps the handle pressed down, so you're forced to hold on to the handle to keep pumping gas. It puts an end to the messing around to build up static, but I don't like this approach. Instead of making me hold down the handle, it just encourages me to use other gas stations that leave the retention clips in place.

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Not to say it doesn't happen, of course, but the problem may not be as serious as you think. An explosion only happens if the fuel/air mixture is just right, which isn't that common at gas stations, or we'd hear about a lot more explosions.

Instead of trying to ground the car, the pump, and the user without creating a spark near the pump, a better approach might be to have some sort of sensor that sounds an alarm in the presence of dangerously high concentrations of gasoline fumes in the air.

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    \$\begingroup\$ You don't need an explosion. A fire is bad enough. Gasoline vapors are very flammable. \$\endgroup\$
    – Kaz
    Commented Oct 10, 2012 at 4:53
  • \$\begingroup\$ Amusingly, since answering this question five years ago I have become a CFEI, so I can answer this a little more definitively now! You're not going to get a fire from gasoline vapors unless the vapor concentration is in a particular range; below the lower explosive limit, there's not enough fuel to burn, and above the upper explosive limit there's not enough oxygen. So as long as you keep the fuel/air mix below a particular range, you won't see combustion from gasoline fumes. \$\endgroup\$ Commented Apr 4, 2017 at 14:07
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I am of an understanding there is a Ground wire in the delivery hose.
Much the same as the cable found in washing machine fill hoses.
A static danger does exist while filling a gasoline container,
so a warning sign is posted at the pump island,
to place the container on the cement or a specifically designed holder.

I have seen people smoking while pumping gas, to read the "No Smoking" sign.
Remove the cigarette from their mouth, and discard it in a puddle of spilled gas.

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