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Shocking Reminder

DanH

Legacy Member
Mentor
I was puttering around the hangar and just happened to notice a slow drip from the fuel tank sump drain. Ran a few shots of fuel into the trusty fuel tester in hopes of flushing the trash from under the o-ring. It just got worse, so I retrieved a wrench, a spare drain valve, and a catch pan, then crawled up under the airplane to do the swap. I reached for the dripping valve......and discharged a fat blue lightning bolt about an 1/8" long directly to the wet brass.

It didn't light. No bandages and I still have an airplane.

No idea how I managed to build a static charge so quickly, but I did, and the lesson is clear. Discharge yourself by touching some metal part of the airplane before you reach for any fuel component....in particular valves dripping fuel.
 
Thanks !!!

... for the warning and reminder. It's So-o-o-o-o easy to forget some of those basics when "puttering around" in the hangar.
 
Gasoline, being a non-polar dielectric substance, dripping to the ground from an insulated conductor (the airplane, being insulated from the ground by the rubber in the tires) can form an electrostatic generating system, sort of like a variant of a Van de Graaff generator. The plane is the upper electrode, the ground is.... well the ground, and the falling gasoline drops act like the dielectric belt transferring electrons to the ground. Given enough drops of fuel hitting the ground and the plane can build up enough of a static charge to make a spark like that.
 
Do you have carpet in the hanger you walk on?

Yes, and I should have mentioned it. However, it is narrow (about gear-wide) and its been there about 15 years without issue. I crawled on it 4 feet, maybe 6 tops, from in front of the left wheelpant to where I could reach the right drain. I suppose that's enough to charge up a 220 lb Swedish-Irish-English capacitor. The mystery is why I didn't get a spark on previous trips; I went under to examine the problem (leaking at threads or through the valve?), then again with the trusty fuel checker, and a third time with the wrench.

My conclusion is it doesn't matter how the airplane and I developed a difference of potential. There's no way to track all the possibilities on any given day; doing so is not an effective prophylactic. What I need to remember is to always touch my aluminum gear leg before touching the drain.
 
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Glad to hear you're okay, Dan. I knew your "electric" personality might get you in trouble some day. ;) (P.S. Stop rubbing ballons on your hair before you work on your airplane.)
 
Thanks for the reminder Dan, glad all is well.
Your story "sparked" my interest in your post and of all the benefits of using mogas, the build up of static when fueling is the one part that causes me the most concern.
I use 2 sets of ground cables, one for the plane and one for me and I never let go of the gas can, so far so good.
 
Gasoline, being a non-polar dielectric substance, dripping to the ground from an insulated conductor (the airplane, being insulated from the ground by the rubber in the tires) can form an electrostatic generating system, sort of like a variant of a Van de Graaff generator. The plane is the upper electrode, the ground is.... well the ground, and the falling gasoline drops act like the dielectric belt transferring electrons to the ground. Given enough drops of fuel hitting the ground and the plane can build up enough of a static charge to make a spark like that.

Aircraft tires are designed to be somewhat conductive (below 10^5 ohm-cm) for static dissipation. Carbon black is added to the rubber mix. They are not rubber insulators.

However, even with this conductivity, grounding mechanically is a good idea...
 
Aircraft tires are designed to be somewhat conductive (below 10^5 ohm-cm) for static dissipation. Carbon black is added to the rubber mix. They are not rubber insulators.

However, even with this conductivity, grounding mechanically is a good idea...

I learned my "one" thing from VAF today. Never had any idea. Thanks Gil.
 
Grounding

Although rare, I've certainly heard of static spark induced tank fires that happen. Low probability and large consequences means it still needs to be on everyones radar. It certainly is easy enough to always use a battery jumper cable from the exhaust to the hanger door or track. But you, the person, also needs to have the same ground potential as the airplane and standing on a charged carpet doesn't necessarily make you grounded.

I think everyone can agree that cold dry air clearly plays a role in static charge as well as carpets. Dan's point is well taken, ALWAYS consider the spark potential.
 
I learned my "one" thing from VAF today. Never had any idea. Thanks Gil.

Thanks... that goes back to Liverpool Quarry Bank high school physics classes dealing with cars, lightning strikes, and Faraday cages.

It might have been half a century ago, but I still remember some of the stuff...:)
 
Hanger Ground

When we built the new 10 place T-Hangers here, with some of the Feds money, they made the contractor put a ground rod and in floor receptacle in every hanger to make it easier to ground the planes. Now, I've tripped over it a number of times during final assembly and still do. I guess I'll put it to use in the future!

Glad to hear you're okay Dan.
 
Keep ones hair conditioned, skin lotioned, try different shoes and hang a hygrometer up at the hanger. When relative humidity is below 40% be extra careful.
 
Back when I lived in Prescott, AZ I had to drop the fuel tank on my 4-runner. It was a dry breezy day and I was laying an the ground under the car. Everytime i touched any part of the vehicle I could feel the current flow. It wasn't a shock like I am used to, but a burning sensation anytime I contacted with any soft-skin areas (like underside of forearm, wrist). It felt like I was touching a hot surface. I opted to put off working on the tank to a later date.
 
I had a friend do exactly that and loose his airplane, hanger and everything in it including other airplanes and cars. Anytime I do anything with the fuel I push the plane outside and ground the plane. It was quite a shock to him when he literally started the fire with his own hands:eek:
 
Fire

A number of years ago I was working one Sat. alone, in the hangar. This was in northern Vermont, winter time and cold out. I had finished a lengthy restoration on a Cherokee and had made a decision to weigh the airplane,
starting by draining all the fuel from the tanks. I had placed a plastic milk carton under the wing and on top if I had placed an empty 5 gallon laquor thinner pail, a clean, steel container with a plastic pour spout incorporated in the top of the can. In the can I then placed a large galvanized funel, resting in the plastic pour spout. I then opened the fuel drain to drain the remaining fuel in the tank, it ran a full stream into the funel.
I was puttering around the hangar for a short time and decided to check the fuel in the can, I did not want it to overflow. Approaching the plane I bent down to check the can and touched the wing, I herd a faint snap, but did not feel anything, looking down at the funel and FROZE. A perfect blue FLAME was migrating up the side of the funel, the funel was 1/2 full of fuel and a full stream was still running into it. A fire extinguisher was on the wall 20' away?? Why I did what I did, I do not know, but I took a deep breath and blew on the flame (IT WENT OUT)
My knees were shacking so bad, I could not stand, I sat on the floor to catch my breath. Had I have gone for the extinguisher, there is no question that the fire would have progerssed up the side of the funel to the fuel and expolded. I was stupid and lucky, not a good combination.
Dick
 
i found that when i get a drippy fuel tank drain that turning it around a few turns helps stop the dripping.
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