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Fire caused by static spark

Anti-static products and coatings

by Chris Woodford. Last updated: September 16, 2013.

Static electricity can be brilliantly useful: photocopiers and laser printers wouldn't work without it. But think about lightning for a moment and you'll see it can also be pretty scary. Although static isn't harmful by itself, when large amounts of it build up and suddenly discharge you can get dramatic and dangerous sparks (it takes about 3000 volts to make a spark just 1mm long). Set off a spark where there's something flammable (such as gasoline fumes) and, before you know it, you've got yourself a fireball and an explosion. You don't need lightning-sized amounts of static to cause problems: even a tiny spark can be problematic in some situations. If static has built up on your body through walking on a rug, and you start handling delicate electronic components, the sudden discharge of current from your body can be enough to cause some very expensive damage. That's where anti-static products can help. Let's take a closer look at how they work!

Photo: This alarming fire was caused when a spark ignited the gasoline fumes from a fuel truck. Photo by Adrian Cadiz courtesy of US Air Force.

Where does static come from and where does it go?

A girl's hair blows out with static when she touches a Van der Graaf generator

If you've read our main article on electricity, you'll know that static electricity is (as the name suggests) a kind of electric charge that stays in one place—it really is static. It's the opposite of current electricity (also called electric current), which is electricity that moves from one place to another along a definite path called a circuit.

Static generally builds up when insulators (materials that don't conduct electricity very well, like plastics, rubber, and so on) or insulated conductors are rubbed, such as when you rub a balloon repeatedly on your clothing. You'll sometimes see this referred to as the triboelectric effect—from the Greek word tribos meaning rubbing—though that fancy expression doesn't really add much to our understanding: it's not the rubbing that's important, but repeatedly bringing the different materials into contact (which rubbing achieves very effectively). You can read a full explanation in our article about static electricity.

Photo: Unfortunately, static electricity isn't always as entertaining as this. Photo courtesy of Sandia National Laboratories/US Department of Energy.

Static electricity can be really useful and we harness it in all kinds of practical ways. When you take a flash photo with your camera, for example, you have to wait a few seconds for static electricity to build up in a capacitor (an electricity storage device). Once the capacitor in your camera is fully charged, a light comes on, and when you press the shutter button, the capacitor discharges rapidly through a powerful xenon bulb, creating a brief flash of light and often a surprisingly loud crack, like a mini bolt of lightning. What's happening here? To get rid of static electricity, we have to turn it into current electricity by creating a circuit. That's what happens in lightning: so much electric charge builds up in a cloud that the air between it and the ground no longer acts as an insulator. Effectively, the air suddenly turns into a giant circuit that becomes visible—as a lightning strike—as the electricity flows down it to Earth.

Anti-static strip hanging from the back of a car

How anti-static products work

To stop static, you have to ensure electricity never has a chance to build up. In other words, you have to make sure there's an electric circuit of some kind to carry any electric charge harmlessly away. Anti-static products do this in all kinds of different ways, sometimes physical and sometimes chemical.

Physical methods

You've probably seen cars driving along with little black strips dangling down from the back touching the road. A car's metal body, riding on rubber tires, builds up a static charge as it drives down the road with air rubbing past it. The theory is that strips like this prevent static electricity from building up on the car body, reducing radio interference, electric shocks when you open the doors, and car sickness. Do these things work? I have absolutely no idea, but one thing is certain: to do anything useful, they must be connected both to the metal car body and touching the ground, completing an electric circuit between the two—and if they're dangling in mid-air (as many of them are) they're a complete waste of time.

Photo (left): An anti-static car strip. Look closely and you'll see a zig-zag of copper wire running across the surface. This is what carries the static electricity to the ground.

If static electricity is a problem on cars, imagine how much more of an issue it is on airplanes, flying at greater speed and with much more surface area brushing through the air. You may not have noticed, but many planes have little carbon-fiber rods or wicks placed at the back of the fuselage to concentrate static electricity into a point and discharge it more effectively. They also help to dissipate electric charges if a plane is struck by lightning in flight. There are some good photos of the wicks on a Boeing 737 on this page from aerospaceweb.

Handling a hard drive wearing an anti-static wrist strap

Static warning label on a printed circuit board

Static isn't just a problem for vehicles that move; it can affect moving people as well. If you have floor coverings made from synthetic fibers, you probably get a static charge every time you walk over them. That's not normally anything to worry about, but it can be a problem if you're working in an office with sensitive electronic or computing equipment. That's why, if you're soldering sensitive electronic components into a circuit, it's usually a good idea to wear an electrically conducting wrist-strap to carry any static safely to Earth. Factories and work places often use anti-static flooring (rubber mats or carpets) to save the need for everyone to wear straps. They look just like normal floor coverings, but they're made with a good proportion of electrically conducting carbon fibers dotted among the ordinary rubber or nylon (synthetic plastic) fibers.

Photo: Static electricity and electronics don't mix! Left: Electronic components often come in packets with warning labels like these attached. Take precautions, such as (right) wearing an anti-static wrist strap when you handle them. A wire runs from the strap around my wrist to a ground (Earth) connection.

Chemical methods

These are physical solutions to the problems caused by static electricity, but there are chemical solutions too. Anti-static spray coatings typically consist of a conducting polymer (plastic) and a solvent made from deionized water and alcohol. When the solvent evaporates, it leaves behind an invisibly thin conducting "skin" on the surface of the object that prevents static build-up. Some washing detergents also have additives to reduce static crackling in synthetic fibers (used in clothes made from materials such as polyester). They work by allowing the fibers to retain a little moisture, which makes them more electrically conducting and reduces the chances of static building up. Very simple—and very effective!

A length of anti-static tubular hose pipe.

Pipelines and hoses are another place where static electricity can cause problems. Static is a particular concern in pipes that carry flammable chemicals, but it can also be a nuisance in ventilation or cleaning pipes where a buildup of static can cause a gradual accumulation of dust and blockage. Most pipes are now made of plastics, which only adds to the problem. Anti-static pipes avoid static buildup either with conducting additives added to the plastic or a coil (or line) of highly conducting wire (typically something like copper) running through them. They can usually be connected to ground at intervals as well.

Photo: Anti-static hose is designed to conduct static electricity either using additives in the plastic or a coil (or line) of metal wire running right through.

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If you're interested in the nitty-gritty detail of how chemical anti-static products work, these patents might be worth a look:

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Text copyright © Chris Woodford 2009, 2012. All rights reserved. Full copyright notice and terms of use.

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Woodford, Chris. (2009) Anti-static products and coatings. Retrieved from http://www.explainthatstuff.com/howantistaticcoatingswork.html. [Accessed (Insert date here)]

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