Static electricity shock: Can it ever be lethal?

[rollingstein]

I was wondering, is it possible to charge oneself with static to an extent that would be lethal or even damaging to a significant extent beyond the usual discomfort?

What are the governing calculations? Instead of the usual carpets would any other materials in an exceedingly dry climate give rise to potentials where you could essentially self-shock to a greater extent?

 

[russ_watters]

Yes. Have you seen the movie The Hunt for Red October? Helicopters generate a potentially lethal static charge.

 

[rootone]

Sitting on top of a van de graff generator then jumping on to the floor would be definitely be unhealthy for you.

 

[sophiecentaur]

Sitting on top of a van de graff generator then jumping on to the floor would be definitely be unhealthy for you.

"Unhealthy"? Kids love to charge up on a School Van der Graaff and then discharge onto someone else or an Earth connection. And Health and Safety doesn't get a mention in risk assessments.
Of course, it depends upon the size of generator involved. They do make them with spheres of several metre diameter. The Capacitance (along with the final voltage - wrt Ground) will govern the charge stored. This link will tell you the capacitance of a sphere and you could take a final voltage of, perhaps, 500kV. Then use Q = CV
The basic limitation of Capacitance of a simple sphere is pretty self limiting, I think.
OTOH, an old fashioned Leyden Jar or a commercial high voltage 1μF capacitor would be more than capable of storing enough Oomph to spoil your day with only a modest few kV. You really need to be careful of those devils.

 

[rootone]

Yeah I was thinking of the big impressive ones which can make 'lightning' which is several meters long.

 

[sophiecentaur]

Yeah I was thinking of the big impressive ones which can make 'lightning' which is several meters long.

Yes. The numbers count though. I would hate for someone to get phobic about a little thing sitting on a lab bench.

 

[Svein]

Remembering - 40 years ago I moonlighted as a medical instrument serviceman. One of the things I serviced was a heart defibrillator (a heart starter). It contained a capacitor (I seem to remember 8μF) which was charged to a fairly high voltage (at least some hundreds of volt) and then discharged across the chest of the patient. I did not see it in operation, but I am told the results were spectacular.

 

[rollingstein]

Thanks. Well, obviously capacitors can kill. And so can Van de Graf generators I guess.

My question was more along the line of what Russ Waters answered. i.e. an incidental side effect of another activity that leads to static charging.

e.g. Say a large tank being filled up. etc. (earthing neglected)

 

[rollingstein]

Yes. Have you seen the movie The Hunt for Red October? Helicopters generate a potentially lethal static charge.

Ah yes, this one?

 

[anorlunda]

If you're surrounded by explosive vapors, yes.

But we should be able to calculate it. Wikipdedia says, "The Human Body Model for capacitance, as defined by the Electrostatic Discharge Association (ESDA) is a 100pF capacitor in series with a 1.5kΩresistor[1]"

Suppose we charged up the body to 1 million volts (very high). Then the charge will be 100 pf * 1 MV = 0.0001 columbs of charge. Now suppose we discharge all of that in one millisecond as a spark. The average current is 0.0001/0.001 = 0.1 ampere for 1 millisecond.On the subject of electrocution, Wikipedia says, "Death can occur from any shock that carries enough current to stop the heart. Low currents (70–700 mA) usually trigger fibrillation in the heart, which is reversible via defibrillator but can be fatal without help. Currents as low as 30 mA AC or 300-500 mA DC applied to the body surface can cause fibrillation. Large currents (> 1 A) cause permanent damage via burns, and cellular damage."

So, on the basis of an order-of-magnitude estimate, yes it is possible to kill yourself this way. All you need is a megavolt voltage source in your house. On the other hand, that amount of shock is about 1/8 that of a defillibrator and (I think) approximately equal to that of a taser but for only one millisecond istead of seconds with a Taser zap. Both of those devices are considered non-lethal.

 

[rollingstein]

If you're surrounded by explosive vapors, yes.

Agreed. Static near a tank of, say, gasoline is a short road to another world.

 

[rollingstein]

So, on the basis of an order-of-magnitude estimate, yes it is possible to kill yourself this way. All you need is a megavolt voltage source in your house.

Nice calculation.

But how do you calculate the other part? e.g. Walking on a carpet on a dry day charges you to how many volts? Is there a back-of-the-envelope way to estimate that?

 

[Baluncore]

So, on the basis of an order-of-magnitude estimate, yes it is possible to kill yourself this way.

If you have a 100pF body, charged to 1MV relative to ground, the safety of the discharge will be dependent on the path taken by the discharge current. It is unlikely that significant current will flow through your heart on route to the ground. That usually only happens when your two arms close a circuit, or when current flows through an arm and then a leg to ground.

The discharge path will be from a small patch of your surface / skin to some grounded object. Just prior to breakdown, charge will be moving towards the side of your body closest to the ground. Breakdown will actually begin with a corona discharge at a distance of about one metre. With 1 MV you can expect a flash burn over the area of skin near the discharge point. The energy released will be about 50 joule.

Skydivers are subjected to the 30V/ft Earth potential gradient. A jump from 10,000 feet would represent a potential difference of 300kV. They do not get electrocuted on landing. Why?

 

[rollingstein]

Skydivers are subjected to the 30V/ft Earth potential gradient. A jump from 10,000 feet would represent a potential difference of 300kV. They do not get electrocuted on landing. Why?

A gradual discharge as they descend?

 

[OmCheeto]

Nice calculation.

But how do you calculate the other part? e.g. Walking on a carpet on a dry day charges you to how many volts? Is there a back-of-the-envelope way to estimate that?

I don't know that there is a back of envelope method, as there are lots of variables.

An Investigation of Human Body Electrostatic Discharge
Nov 1993

In an ESD event, the human body can reportedly generate static charge levels as high as 15,000 volts by simply walking across a carpeted floor and 5,000 volts by walking across a linoleum floor.

It would be a fun experiment to do though.
It looks like the components you need are sitting around the house, and on your head.
You would want non-conducting materials from opposite ends of the following list:

The TriboElectric Series
When two different materials are pressed or rubbed together, the surface of one material will generally steal some electrons from the surface of the other material. The material that steals electrons has the stronger affinity for negative charge of the two materials, and that surface will be negatively charged after the materials are separated.
...
[list of materials]
...

Hair and Teflon look like good choices.

This is interesting:

"Saturation", or maximum charge that can be transferred: Beyond a certain amount of charge transferred, additional friction energy (rubbing) does not produce any additional charging. Apparently, two effects limit the amount of charge per area that can be transferred. If the spark E-field (10 KV/cm) is exceeded, the two surfaces will spark to each other (after being separated from each other by at least about 1 mm), reducing the charge transferred below 10 KV/cm.
...

 

[anorlunda]

With respect to the lethality of sparks, the big problem is the difference between what is possible and what is probable.

It may be true that someone could have their heart stopped by a tiny discharge. But past era designers of electric chairs found out that certainty of death can be very elusive.

The lethality part of the question is not electrical engineering, it is biology.

 

[nsaspook]

Yes. Have you seen the movie The Hunt for Red October? Helicopters generate a potentially lethal static charge.

I worked in combat cargo for a bit, we had the standard grounding kit. Once you get zapped you never leave home without that grounding rod.
http://www.globalsecurity.org/military/library/policy/army/fm/10-67-1/Image620.gif

 

[Baluncore]

The two materials rubbed together would need to be connected to the body and to ground. If it required 1MV on a 100pF body to be lethal, then the insulation would need to be 1 metre thick to prevent corona breakdown through the surrounding air. But triboelectric materials are insulators so the triboelectric charge would not appear between the body and ground. So the air that you breathe protects you from self-inflicted electrocution by friction generated static. To generate a lethal charge you would need a capacitance significantly greater than the 100pF of a human body.

 

[rollingstein]

It looks like the components you need are sitting around the house, and on your head.

What about the instrument to measure the voltage? After making my little brother walk across the linoleum for 6 hrs what do I measure him with?

 

[rollingstein]

It may be true that someone could have their heart stopped by a tiny discharge. But past era designers of electric chairs found out that certainty of death can be very elusive.

The median heart I guess.

 

[anorlunda]

What about the instrument to measure the voltage? After making my little brother walk across the linoleum for 6 hrs what do I measure him with?

That's a very good question. The amount of charge involves is so tiny that any regular voltmeter with a finite input impedance, would drain away the charge as soon as it is connected. I don't know the answer.

 

[jim hardy]

e.g. Walking on a carpet on a dry day charges you to how many volts? Is there a back-of-the-envelope way to estimate that?

here's a test report(random search find) for carpet, looks like a few KV for that sample
.http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0CCwQFjAC&url=http://www.patcraft.com/infopacket/test/I0299&ei=9AQxVaCJPIHvoAS_wYBY&usg=AFQjCNGQKyJJmxHcRkkuuHxHqhre_hJUhw&bvm=bv.91071109,d.b2w

they use an :Electrostatic Voltmeter", basically a capacitive device.

 

[jim hardy]

see also

https://www.physicsforums.com/threads/static-electricity.752719/

 

[DaveC426913]

What about the instrument to measure the voltage? After making my little brother walk across the linoleum for 6 hrs what do I measure him with?

You are the measurement instrument, and the units are guffaws per tear.

"Experiment 123b (dry winter day, wool pajamas) generated an unprecedented 14.3 guffaws per tear. "

 

[rollingstein]

I worked in combat cargo for a bit, we had the standard grounding kit. Once you get zapped you never leave home without that grounding rod.

Do you see a spark / discharge when a helicopter lands typically? Say at night. I've never noticed this. But if it indeed gets charged so much I'd expect one.

 

[OmCheeto]

What about the instrument to measure the voltage? After making my little brother walk across the linoleum for 6 hrs what do I measure him with?

You could build an "electroscope".

According to wiki, it was the first electrical measuring device.
I've never made one myself.
I still haven't put together my Wimshurst machine, so I've no need for one.

 

[rollingstein]

You could build an "electroscope".

Aren't those qualitative? Can they tell if I've been charged to 500 V or 25,000 V by static?

 

[anorlunda]

You could build an "electroscope".

According to wiki, it was the first electrical measuring device.
I've never made one myself.
I still haven't put together my Wimshurst machine, so I've no need for one.

Yes, excellent. Here is a page about some beautiful and calibrated electroscopes.

http://physics.kenyon.edu/EarlyApparatus/Static_Electricity/Electroscope/Electroscope.html

 

[OmCheeto]

Aren't those qualitative? Can they tell if I've been charged to 500 V or 25,000 V by static?

Everything is qualitative, until you start measuring things.

The following site lists some relevant physics equations, and different types of electroscopes.
I would read and dissect it for you, but I'm short of time today.

Electrostatics at Home
Work on your kitchen table with the forces that hold matter together

 

[nsaspook]

Do you see a spark / discharge when a helicopter lands typically? Say at night. I've never noticed this. But if it indeed gets charged so much I'd expect one.

I've seen it many times during landings on metal decks but typically with shipboard combat cargo the bird never lands, you hook the sling to the underside cargo hook.
At the time I was a sailor (LPH-3) working for a USMC gunny sgt. As you can see it's very easy for things to get a little too close and get zapped.
Cargo ops.


Static discharge.