Static electricity from vacuuming up spilled kitty litter

[james_s]

I've observed an interesting phenomenon recently that I've been meaning to bring up. I have one of those Dyson cordless vacuum cleaners and I've found that when I vacuum up spilled clay kitty litter it generates a tremendous amount of static electricity. It's enough to cause a small lightning bolt to shoot out of the charging jack every few seconds, discharging painfully to my palm. If I hold my hand away from that area it will discharge even further from around the trigger to my finger, it's like a Van de Graaff generator. I noticed this same effect with the identical vacuum my mom has but I've not yet found anything other than kitty litter that causes it to happen. Does anyone know why litter in particular does this? Clay is not a material I typically associate with static electricity.

[Mr. Scram]

That sounds like the triboelectric effect to me. Which combinations of materials charge effectively can be fairly unpredictable.

https://en.wikipedia.org/wiki/Triboelectric_effect

[TheSteve]

I get that when vacuuming the couch with our V8 - it keeps you awake and reminds you that you're alive

[ogden]

That sounds like the triboelectric effect to me. Which combinations of materials charge effectively can be fairly unpredictable.

https://en.wikipedia.org/wiki/Triboelectric_effect

Actually material combinations are well known. Even in wiki article there's list of Triboelectric series. Cat litter is not pure clay, even natural clay itself contain other minerals such as quartz (mostly positive) which is quite far from plastics (mostly negative) in Triboelectric series. So, everything was as it should be - sparks flying

[james_s]

Interesting, thanks. I noticed if I hold onto the aluminum extension tube it seems to prevent a charge from building up so maybe I'll try adding a static discharge wire between that and the hand grip. It's quite a bit more potent than the typical doorknob on a dry day zap, I worry that it will damage the electronics in the vacuum as it has one of those fancy electronic brushless motors. It's also quite painful and unpleasant to get shocked repeatedly.

[Mr. Scram]

Actually material combinations are well known. Even in wiki article there's list of Triboelectric series. Cat litter is not pure clay, even natural clay itself contain other minerals such as quartz (mostly positive) which is quite far from plastics (mostly negative) in Triboelectric series. So, everything was as it should be - sparks flying

You're misunderstanding me. There isn't really a good rule of thumb what material interacts how with what, although we obviously have empirically established that the other way around by now. That's not the same, though.

[John Heath]

Interesting, thanks. I noticed if I hold onto the aluminum extension tube it seems to prevent a charge from building up so maybe I'll try adding a static discharge wire between that and the hand grip. It's quite a bit more potent than the typical doorknob on a dry day zap, I worry that it will damage the electronics in the vacuum as it has one of those fancy electronic brushless motors. It's also quite painful and unpleasant to get shocked repeatedly.

I found a trick for the door knob surprise that could be used for the vacuum cleaner surprise. I came to a point that I could not touch the door knob without swatting at it first just to get the electric shock over with. My solution was to carry a HV 100 M ohm resistor in my pocket. When it came time to touch the door knob it would be done through the 100 M ohm resistor. It still makes a spark but you can not feel it. A HV 100 M ohm resistor from the charge plug to the vacuum handle should do it. This way you will be continuously discharging the static charge but at a low current so you will not feel it. Not a bad suggestion to pass on to the manufacturer of the vacuum cleaner.

[Brumby]

Same trick - but I use my keys or some other metal object if I don't have my keys on me.

Still get the spark - sometimes with a resounding crack - but the point source comes off the metal, not my fingers.  I daresay the much greater contact area between my fingers and the key allow the passage of current to pass unnoticed.

[amyk]

Even making the plastic casing slightly conductive would probably solve this problem.

There's a similar problem with treadmills (the ones you walk/run on) --- those can deliver a powerful shock if the belt isn't grounded to the frame with a "collector", since they basically form a horizontal Van de Graff.

[floobydust]

It's important - vacuuming your PC or any electronics, or using compressed air to blow out dirt, makes a lot of static electricity.

I've seen many techs damage boards by simply cleaning them this way. 3M has their anti-static vacuum cleaner, conductive plastic hoses.

[Tomorokoshi]

Get a soft lead pencil, grind it up, and vacuum up everything? Perhaps the graphite will coat the inside and make a dissipative layer. Or just work it in some other way.

I've seen vacuums for sawdust with a wire running down the length of the hose to vacuum motor to dissipate static. Dusts can be explosive, and the spark could set it off.

[james_s]

I used to regularly clean PCBs using compressed air, then I read about the static issue and stopped doing it. I can't conclusively say that I have ever damaged one that way but looking back I do suspect a few incidents.

With the vacuum I found I can hold onto the aluminum wand instead of just the handle and that keeps a charge from building up. I'm really tempted to add a discharge wire or paint a track of carbon paint from the wand attachment to the handle. The thing that surprised me the most was the fact that of all the various things I've vacuumed up, kitty litter is the only thing that has been giving me shocks, and they're impressively powerful.

I once had a pair of sneakers in which the fabric covering the inner sole had come loose and would rub on the foam as I walked. Just walking a few feet and touching a metal object was enough to give me a powerful shock.

[Red Squirrel]

I had a funny incident like that once.  I was experimenting with trying to get chemical smell out of my couch because my cat pukes so much and after dousing the couch with every chemical I can find to try to get rid of the puke now all I could smell was the chemicals.  So I tried to just pour an entire box of baking soda on it and let it sit for a day or two.  When I vacuumed it up with the central vac it created a crazy amount of static, considering it was dry powder going through a very long plastic hose!  I was almost like Palpatine shooting lightning from my arms while vacuuming.   

It ended up causing an issue with a nearby temperature sensor and I had to reset my home automation system to get the sensor to work again. 

I imagine with some kind of high speed air pump and plastic tubing loop with baking soda in it you could make a pretty decent van degraaf generator.  One section of pipe could be metal with a rod sticking out and it would probably discharge quite nicely.

[ogden]

I found a trick for the door knob surprise that could be used for the vacuum cleaner surprise. I came to a point that I could not touch the door knob without swatting at it first just to get the electric shock over with. My solution was to carry a HV 100 M ohm resistor in my pocket. When it came time to touch the door knob it would be done through the 100 M ohm resistor. It still makes a spark but you can not feel it. A HV 100 M ohm resistor from the charge plug to the vacuum handle should do it. This way you will be continuously discharging the static charge but at a low current so you will not feel it. Not a bad suggestion to pass on to the manufacturer of the vacuum cleaner.

Other option is to ship vacuum cleaner with ESD heel strap, something like this:

http://ultrastatinc.com/ESD_Heel_Strap_for_Static_Control.html

Actually those who tinker with electronics (even at home), shall consider ESD footwear in their lab:

http://www.antistat.co.uk/section.php/151/1/esd-shoes

[ogden]

I used to regularly clean PCBs using compressed air, then I read about the static issue and stopped doing it.

High-pressure compressed air indeed is not the best tool for the job, especially when board you are cleaning, is not grounded to you and/or air nozzle. Better use "canned air" which is actually not air but mostly butane, also ground device you clean - strap it to yourself using ESD strap. Using "canned air" there is another danger - possibility of combustion/explosion So ventilate your electronics well after cleaning & before switching it on.

[Terry01]

I have 2 things here......

No1. Get the Mrs to do the hoover thing and I guarantee you won't get no more shocks from the hoover....can guarantee it 100%! 

No2. Cleaning with compressed air;

I used to work in the building trade...Roads and sewer gang.
One hot summer day our hired in for the week 360* track machine operator was moaning about the dust in his cab, he was going his duster about trying to keep it clean for the regular operator and when he was stuck in there all day breathing in all the dust. The young lad who worked with us said he'd seen another operator cleaning his cab out with the compressor hose for the jack hammer etc....
I've seen this before and i nearly broke my neck running for the other 2 guys in my gang when I heard the 2 talking about doing this. This couldn't be missed! These things pump out about 8 bar or more or well over 100 odds PSI!
These 2 were going to blast the open end of the hose into a dust filled 360* digger cab!
It can be done if you slowly open the valve but it's a crap way to do it at the best of times...I knew this wasn't going to be the case with these 2! I couldn't wait!! 
The operator took the hose cause he wanted to be in charge of the operation and the young lad was in charge of opening the valve...the driver shouted "RIGHT" there was a massive WHOOOOOSHHH and the service manual and all the drivers check sheets etc went flying over his head just as he disappeared into a massive dust cloud!   

He went nuclear and the look on the young boys face was priceless as the dust settled...the tears were rolling down my face i was laughing so hard! The other 2 guys and i were killing ourselves laughing when one of them asked "do you think it needs another quick blast driver"?   

Funny as hell! One of the funniest things i've ever seen! Don't try this at home kids! 

[amyk]

High-pressure compressed air indeed is not the best tool for the job, especially when board you are cleaning, is not grounded to you and/or air nozzle. Better use "canned air" which is actually not air but mostly butane, also ground device you clean - strap it to yourself using ESD strap. Using "canned air" there is another danger - possibility of combustion/explosion So ventilate your electronics well after cleaning & before switching it on.

Canned air is usually a nonflammable fluorocarbon. It used to be R-12 in the good old days... but I'd be very surprised if it's butane now, because butane burns explosively and really, really well.

[james_s]

I have a can of air duster here, it says it's difluoroethane. They add stuff to make it taste bitter to prevent inhalant abuse, makes it smell bad too. Personally I'm of the opinion that if someone is dumb enough to inhale air duster to get high, there's no point in trying to protect them from themselves.

[Red Squirrel]

That bitterant stuff is nasty!  At a place I worked we used to prank each other by freezing the thermostat so the heat would kick on even if it was hot in the room.  We stopped that pretty quick when they switched the cans to the ones that have bitterant. 
 
That said I'm not a fan of air dusters, it's so wasteful.  I prefer an air compressor.   Just need to be careful about moisture.  You can get air dryer attachments but was never able to actually find some so never bothered, but if I was doing it a lot I'd look harder to try to find some.

[ogden]

Canned air is usually a nonflammable fluorocarbon.

Did my homework. #1 choice of today's dusters is 1,1-Difluoroethane. Not as explosive as butane, but far from nonflammable: "Hazard statements : Extremely flammable gas."

https://www.airgas.com/msds/001090.pdf

but I'd be very surprised if it's butane now, because butane burns explosively and really, really well.

You are right. I was ill-informed with 20th century knowledge.

[james_s]

I too prefer an air compressor, but there are times when the portability of the canned air makes it worthwhile. I can't easily drag my air compressor around the house.

[james_s]

A better solution would be a ground wire connecting the extension tube to a conductive pad on the handle to keep the charge from building up. I've formed a habit of grasping the tube with my left hand while using the vacuum.

[Domagoj T]

Some shopping centers have horrible static around them. I don't know if it's the floors or what but, whenever I'm in one of those I insist on being the one to push the cart. That way I can bump a metal shelf to discharge every couple of aisles.

[GeoffreyF]

Actually, the pain one experiences from static is NOT a shock.  The discharge ionizes air creating a shock wave (however tiny).  That's what you actually feel, not a shock.  You can test this by discharging the static with a piece of metal such as a wedding ring, paper clip or whatever.  Obviously the same energy is conducted to your finger in this way but you will feel nothing.

None of this is to say that static discharge cannot harm electronic equipment.  It can. It does.  The damage is also not necessarily completely destructive.  It can degrade a part making it less reliable.  In a computer this would show up as more frequent crashes.

[apis]

You can test this by discharging the static with a piece of metal such as a wedding ring, paper clip or whatever.

But in that case the energy would be spread over a much larger area, so one would expect it to hurt less.

[SeanB]

With shopping trolleys Spar solved that by putting a small 4 link section of chain on the rear wheel, letting the one end drag on the ground, and the bolt for the fixed rear wheel holding the chain. Makro did that as well, seeing as the AC they use is actually effective enough to get the humidity in the building down below 30%, which is pretty impressive considering that it is currently 70%, and 30C, and Makro wants it to be 20C in the store. I used to look for the trolleys with the straps in winter, or just grab a regular one, grab the trolley wipe and clean the handle, and thus leave a film of detergent on it, and then while pushing the trolley bounce off every single steel upright I passed. Often with a loud crack as the spark discharged. New trolleys all have the chains, though they still are no wheel steer at times, or drive like a Taxi.

[Marco]

Clay is a cation exchange medium, so that might play a role as well.

Maybe clay being naturally negative charged is forming a complex with small particles of dust to hold the positive charge and the vacuum cleaning is separating them and expelling the positively charged dust to form a large net negative charge?

[NiHaoMike]

Some shopping centers have horrible static around them. I don't know if it's the floors or what but, whenever I'm in one of those I insist on being the one to push the cart. That way I can bump a metal shelf to discharge every couple of aisles.

On a very related note, a friend of mine, then a medical student, told a story about the time she was working in a research lab of a hospital. At one point, she had to take the elevator, where another worker was transporting a dead body on a cart. All of a sudden, there was the snap of static electricity discharging and she felt "someone" reach out and touch her, which was the dead body that came to life for a split second thanks to ESD. It was not only her scariest moment in life but also the most embarrassing since her scream brought over a crowd to see what all the commotion was about, where they saw that she literally just had the piss scared out of her.

[james_s]

That's hilarious, I remember discovering in elementary school that I could make the legs of a dead frog kick by using a small transformer and touching the wires repeatedly to a 6V battery.

On a related note, the other day I was using a belt polisher at my friend's machine shop while standing on a rubber mat and whenever I touched the body of the machine it would shock the crap out of me. I held the bar I was polishing with the tip about an inch from the machine there was a continuous crackle of sparks between them. It made quite an effective Van de Graff generator.

[jmelson]

That sounds like the triboelectric effect to me. Which combinations of materials charge effectively can be fairly unpredictable.

https://en.wikipedia.org/wiki/Triboelectric_effect

A great one is CO2 fire extinguishers!  They have a plastic "funnel" to direct the CO2, which forms snow as the liquid from the bottle expands.  It will generate sparks strong enough to cause people to fall down in some cases - like a taser!  They had to change the design of the extinguisher to make the nozzle conductive, so that charge didn't build up.  The concern was the spark could re-ignite a fire after you had put it out - and expended the extinguisher.

Jon

[GeoffreyF]

You can test this by discharging the static with a piece of metal such as a wedding ring, paper clip or whatever.

But in that case the energy would be spread over a much larger area, so one would expect it to hurt less.

Use as little a piece of metal as you like.  A pin if you like.  There is no shock from the static electric conditions we are discussing here.   

[Zero999]

You can test this by discharging the static with a piece of metal such as a wedding ring, paper clip or whatever.

But in that case the energy would be spread over a much larger area, so one would expect it to hurt less.

Use as little a piece of metal as you like.  A pin if you like.  There is no shock from the static electric conditions we are discussing here.

I'm not convinced. I know a get a shock from a piezo igniter if I directly touch the wire. I'll have to give it a go with static and a piece of insulated cable. The problem is at the moment the weather is mild and damp, so static charges don't hang around for long. Hopefully it'll get colder and dryer next month.

[james_s]

If I hold one hand on the belt polisher I don't get a shock. If I hold one hand on a Van de Graff generator and the other on a grounded object I don't get a shock. Generally static sources produce very little current, you only get a shock if a charge is able to build up.

[In Vacuo Veritas]

What do you feed your cat? Batteries?

[Terry01]

I have 2 cats.

A mostly black 1 with a couple of white patches and 4 white feet, and a mostly white 1 with some small black patches and a black tail.
I sometimes get small static shocks from the mostly black 1 when I pet him but only very occasionally get the same kinda shock from the mostly white 1. The white 1 is very soft to pet. This may be me gibbering but it seems to mostly happen when the 2 of us are standing up. If say  i'm sitting on the sofa and he jumps up on me to get petted I rarely if ever get the same shock.
A wee bit off topic I know, but maybe someone has the same experience or can tell me why it seems to only happen on the black 1 when we are standing up?

[james_s]

I have several cats and in the winter when it's dry I can pet them and see sparks crackling all over. If I stroke a small fluorescent tube across the cat it will flicker and flash.

[Terry01]

I have several cats and in the winter when it's dry I can pet them and see sparks crackling all over. If I stroke a small fluorescent tube across the cat it will flicker and flash.

Cool 

[GeoffreyF]

You can test this by discharging the static with a piece of metal such as a wedding ring, paper clip or whatever.

But in that case the energy would be spread over a much larger area, so one would expect it to hurt less.

Use as little a piece of metal as you like.  A pin if you like.  There is no shock from the static electric conditions we are discussing here.

I'm not convinced. I know a get a shock from a piezo igniter if I directly touch the wire. I'll have to give it a go with static and a piece of insulated cable. The problem is at the moment the weather is mild and damp, so static charges don't hang around for long. Hopefully it'll get colder and dryer next month.

Not my job to convince you especially when what I explained is black letter physics.  Read a book.

[joeqsmith]

Generally static sources produce very little current, you only get a shock if a charge is able to build up.

I am not sure what "very little" means but certainly several Amps is possible.   I measured around 5A peak with a gas grill ignitor.   The IEC standards call for even higher currents. 

https://www.silabs.com/documents/public/application-notes/AN895.pdf

[james_s]

I think a gas grill igniter is a rather extreme case. The shocks you get from ordinary static are as strong as they are because the charge builds up on your body and discharges suddenly when you touch something. If you hold onto that object and shuffle your feet or whatever was generating the static, no charge will build up and you won't get a shock.

[joeqsmith]

I think a gas grill igniter is a rather extreme case. The shocks you get from ordinary static are as strong as they are because the charge builds up on your body and discharges suddenly when you touch something. If you hold onto that object and shuffle your feet or whatever was generating the static, no charge will build up and you won't get a shock.

I agree that the grill ignitor I use is rather an extreme case in that it has a very weak spark.  The gun I designed to replace it is in the order of 15 Amps peak.   By ordinary static, I assume you mean not simulating it using electronics.   I can tell you that the my personal feeling of the ignitor is that the pain I get when discharging it into my finger is much lower than what I feel when I touch the door knob after walking on the carpet during the dry winter months.   

[IanB]

I think the discussion about static sources relates to peak current vs average current. For example, if you continuously discharged the grill igniter into a suitable RC filter and measured the average discharge current over time, what would it be? Microamps?

[joeqsmith]

We are talking about an event that is measured in 100ns or so.  The IEC standards show the waveforms and measure in peak.  They go into detail how the measurements are made as well.    If you wanted to consider the average current for the duration of the event, it would be easy enough to calculate.   

Just to be clear, obviously as we increase the period that we use for a single event, the average will approach zero.  It just doesn't make a lot of sense to me why one would consider what happens after the event.   The standards use peak currents/voltages and define the decay.  If you look at the current waveform, you can see it is not a nice shape.  Thinking in terms of average current alone would tell you nothing about that initial 800ps. 

Scope shot showing the output waveform from my gun during development (10A peak).  The overlaid waveforms are several events zoomed in. 

[Magicshark]

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[joeqsmith]

I had not seen the coins in a plastic bag before.  Seems the grill starter is the most common source those of us on a budget use.

https://www.edn.com/an-emc-troubleshooting-kit-part-2-esd-immunity/

I know it's and old thread about kitty litter......  A few other links that may be of interest:

https://electronics.stackexchange.com/questions/218024/diy-esd-generator-esd-gun
https://www.researchgate.net/post/Can_anyone_recommend_designs_for_a_high_voltage_switch_for_ESD_test