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Static Electric Discharges and How To Prevent Them Zapping You
It Bit Me!
Did this ever happen to you? You drive somewhere, park, get out of your car, go to lock it up and 'Ouch'! you get a static electric shock. It hurts, but try complaining to your nearest and dearest, especially if it doesn't happen to them. (They are probably not wearing tights.) The spark is painful because the electricity goes straight into your pain sensors, overloading them. It drills into your skin like a white-hot needle, creating a microscopic burn. Fortunately, there are some things that you can do to prevent getting zapped and keep yourself safe.
What Is Static Electricity?
Static electricity is a similar mechanism to lightning, where you have clouds rubbing together and then a spark generated by very dry air above them.
Static electricity means electricity at rest, in contrast to current (or 'dynamic') electricity. It takes approximately 3,000 volts of static electricity for you to feel the smallest bang1. The effects of static electricity are due purely to the electrostatic field produced by the charge, whereas in dynamic electricity other effects, principally an electromagnetic field, are also involved.
All matter is made up of atoms, which in turn are made of particles that have a positive charge, a negative charge, or no charge at all. Protons have what is called a 'positive' (+) charge. Electrons have a 'negative' (-) charge. Neutrons have no charge, they are neutral. The charge of one proton is equal in strength to the charge of one electron. When the number of protons in an atom equals the number of electrons, the atom itself has no overall charge; it is neutral.
The protons and neutrons in the nucleus are held together very tightly. Normally the nucleus does not change, however some of the outer electrons are held very loosely (other materials hold their electrons very tightly). They can move from one atom to another. An atom that loses electrons has more positive charges (protons) than negative charges (electrons). It is then positively charged. An atom that gains electrons has more negative than positive particles, has a negative charge. A charged atom is called an 'ion'.
The atoms of some elements have loosely held electrons which can move from one atom to another very easily, allowing an electrical current to flow. Materials and compounds made from such elements are called conductors. Most metals are good conductors. Some elements however, hold their electrons much more tightly, restricting the flow or electrons from one atom to another and preventing a flow of electricity. Materials made from these elements are called insulators.
To move electrons from one place to another2, rub two objects together, causing friction. If they are made of different materials, and both are insulators, electrons may be transferred from one to the other. The more you rub, the greater the number of electrons that move from one to the other, and the larger the charge that builds up. It isn't the rubbing or friction which causes electrons to move, it's the contact between two different materials. Rubbing/friction increases the contact area between them. If you end up with more negative than positive, (or with more positive than negative), then you have a charge-imbalance on your body. You will get zapped the next time you touch anything metal.
The Imbalance of Positive and Negative Charges
Positive and negative charges behave in interesting ways. Have you ever heard the saying that opposites attract? Well, it's true. Two things with opposite or different charges (a positive and a negative) will attract, or pull towards each other. Things with the same charge (two positives or two negatives) will repel, or push away from each other. A charged object will also attract something that is neutral. When you pull off your woollen hat, it rubs against your hair. Electrons move from your hair to the hat. Now each of the hairs has the same positive charge. Remember that things with the same charge will repel each other. So the hairs try to get as far away from each other as possible. The farthest they can get is by standing up and away from the others. Bad hair day? No, it was static build-up.
Think about how you can make a balloon stick to the wall. If you charge a balloon by rubbing it on your hair, or your woollen jumper, it picks up extra electrons and has a negative charge. Holding it near a neutral object (like a wall or a door) will make the charges in that object move. If it is a conductor, many electrons move easily to the other side, as far from the balloon as possible. If it is an insulator, the electrons in the atoms and molecules can only move very slightly to one side, away from the balloon. In either case, there are more positive charges closer to the negative balloon. Opposites attract: the balloon sticks3. It works the same way for neutral and positively charged objects.
What Does All This Have to do With Shocks?
You are one surface, and the car seat is the other. The contact between your clothes and the seat's surface causes the electrical charges within atoms of the material to transfer between the surfaces. One surface ends up with more negative charges than positive, and has a negative charge-imbalance. The other surface has fewer negatives than positives, so it has a positive imbalance. While driving, you're rubbing your entire back, bottom and legs on the car seat surface. Nothing happens as long as you remain seated4.
However, when you open the car door and step outside, you take just one polarity of charge along with you, while the car seat has the opposite polarity. At the same time, the charged-up car seat causes the whole car to become charged5. As you step out of the car, the voltage between your body and the car builds up, to 10,000 or possibly even 20,000 volts. Your shoes are probably acting as insulators, so the charge has no opportunity to ground. You touch the car door and get zapped. The opposite polarities rejoin by leaping through the air while giving you a tiny, deep burn on your fingertips.
As you walk across a carpet, electrons move from the rug to you. Now you have extra electrons. Touch a metal door handle and ZAP! (the door handle is a conductor). Did the door handle bite you? No, it was static build-up. Put scientifically: contact-electrification between insulating surfaces, followed by separation of those surfaces. Static electric shocks are painful and distressing, but there are precautions you can take.
Things To Try at Home and Workplaces
Electronics stores sell anti-static products but they are expensive initially, and as you may need to keep buying more, you would be wiser to make your own.
Make Your Own Anti-Static Spray
Take an empty spray bottle (such as a window cleaner bottle) and pour in a small amount of fabric conditioner. Fill the bottle with water. The mixture should be about 30:1. Spray the car seats (furniture and/or carpets) and allow to dry. Reapply as necessary.
What Not To Do
Don't use your chipped car key as a lightning rod. Most electronic devices (or at least the chips inside) are static-sensitive, and they have to be labelled as such, and you (the user) must protect them from static discharge. The spark is merely irritating to people but will completely destroy the tiny transistors on a chip.
I just read your column6 concerning static shocks while exiting a vehicle. You said some people use their keys as 'lightning rods'. That was the solution I was using to diffuse the shock as I exited my '97 Lumina until it shorted out the computer chip, a security feature, imbedded in the key. This prevented the car from starting. In addition, these keys are expensive to replace. You may not want to offer this as a solution in the future.
Filling the Petrol Tank
There has been some publicity in recent years about car fires caused by static electricity while refuelling, but it's still not common knowledge. Now that most people pump their own petrol, and also the insulation and grounding properties of petrol tanks have changed by the addition of plastics, more women than men cause fires while refuelling. The theory is that they are more prone to re-enter their vehicles during cold weather, build up a static charge and cause an explosion and fire when touching the pump again. They also wear nylon tights (and stockings). Synthetic materials like nylon and polyester are prone to producing static. Furthermore, the carpets and upholstery in many cars are also made from synthetic fibres.
Important Safety Rules While Refuelling
Supermarket Trolleys, Hospital Incidents and Other Dangers
You are building up the static as you push the supermarket trolley around on the rubber floor tiles of the shop. When you put something in the trolley and you touch the metal, 'Ouch'! Go to take something off a shelf, touch the metal front of the shelf and...
Sparks from static electricity can be dangerous when flammable vapours are present eg, in hospital operating theatres where ether (anaesthetic) has been ignited by a spark from a patient-transport trolley. If the trolley has insulating rubber tyres it can become electrically charged as a result of friction between the blankets and the plastic sheet on it. High tech fire alarms can be set off when nurses shake bedcovers.
A man who was wearing a woollen shirt and a synthetic jacket ignited a carpet when he walked into a building, forcing fire-fighters to evacuate the building. He had unknowingly built up a 40,000-volt charge of static electricity in his clothes, which was just one step short of spontaneous combustion, commented a fire-fighter of over 35 years experience. The plastic on the floor of his car had been scorched. The jacket he had been wearing was tested with a field static electricity meter where it registered a charge of about 40,000 volts.
Fine particles of many common materials; coal, sawdust, sugar, starch, flour etc. can form explosive dust clouds - ignitable by a static spark. Precautions have to be taken in factories to prevent this.
If touching other people gives you (and them) a shock, then you need to find out the cause.
The Triboelectric Series
When various materials7 are touched together, which become positive and which become negative? Starting with the most positive: Air8; Human Hands; Asbestos; Rabbit Fur; Glass; Mica; Human Hair; Nylon; Wool; Fur; Lead; Silk; Aluminium; Paper. Cotton scores zero then the negatives: Steel; Wood; Amber; Sealing Wax; Hard Rubber; Nickel, Copper; Brass, Silver; Gold, Platinum; Sulphur; Acetate, Rayon; Polyester; Styrene (Styrofoam); Orlon; Saran; Polyurethane; Polyethylene; Polypropylene; Vinyl (PVC); Silicon. The most negative is Teflon.
Researchers at Southampton University have developed a cockroach trap. It works because cockroaches are electrically charged enabling them to climb on all manner of surfaces by using the static on their feet. The trap sends out pheromones (irresistible sexual attractants) that attract the cockroaches. Once inside the trap, the insects' feet are coated with an anti-static powder that prevents them from climbing out again. (Reported in 'Inventor's World', 1998).
The ocean liner Lusitania sank when she was torpedoed off the south coast of Ireland in 1915. The force of the explosion startled even the German U-boat commander, and there was speculation that the ship had been carrying explosives. The torpedo penetrated the hold, which was empty except for coal dust, as the ship had just crossed the Atlantic. This may have set off a dust explosion caused by static electricity in the coal bunkers. It is known that aerosolised coal dust can explode violently when a discharge of electricity is sent through it.
Conjurors pull a spray of paper or feathered flowers out of a tiny tube, which then expand into an enormous bunch. Not magic - static.
In the late 1800s, fashionable Parisian women never went out in windy weather unless they had a lightning rod attached to their hats. As lightning is a powerful, natural electrostatic discharge, it's to be hoped they didn't get caught out in a thunderstorm.
Not All Bad
Static electricity has its uses as well as dangers. For example electrostatic precipitators are used in the smoke stacks of coal-fired power stations to precipitate coal dust that would otherwise emanate at a rate of thousands of tons per hour, thus giving rise to particle pollution.
Brushing your hair in the dark can give spectacular sights. Pulling off a sweater can also give off some nice sparks. Read How Hair Conditioner Works and helps prevent you from suffering a bad hair day.
Last but not least: the Van De Graaf generator beloved of science students the world over. You stand on it and in a few minutes your hair is standing on end. It generates huge potential differences and can even be used to create mini-lightning discharges.
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