Static Shocks Are a Seasonal Occurrence, but Science Can Help Us Avoid Them

5 minute read
Originally posted here: https://mcgill.ca/oss/article/environment-general-science/how-can-i-stop-getting-static-shocks

If you live in Canada, you know what a nightmare winter can be for your hair. No, not because of hat hair, (or at least not entirely because of hat hair), but because of static electricity! All those big scarves and wool hats really do a number on the frizziness of our hair. But even if you’re bald you’ve probably noticed that the number of times you get shocked when reaching for everyday items, like keys, doorknobs and shopping carts, increases in the winter too. There’s some interesting science behind these seasonal shocking scenes, and how you can stop them. 

The number one factor influencing how many zaps you get is humidity. But to understand why we need to review a bit about electricity.  When two objects made of different materials come in contact with each other, like your hair and a hat, for example, electrons can transfer between them. The more prolonged contact, the more electrons move, creating an imbalance of charges between your hair and the hat.

Whether the electrons move from your hair to the hat, or vice-versa, depends on something called the triboelectric series. It’s basically a ranking of different materials based on their tendency to lose or gain electrons. Some things, like rubber or acrylic, are very likely to gain electrons and become negatively charged. Whereas other things, like hair, glass or wool, are more likely to lose electrons and become positively charged. In the case of your hair and a wool hat, since human hair is higher on the triboelectric series, the electrons flow from your hair to the toque.

The problem is that same charges repel each other, so now that your hair is full of positive charge, it’s rather unstable. That’s why, when you get near something conductive, like a metal doorknob, electrons from the knob will “jump” to your hair to neutralize the charge, shocking you in the process. It’s also why your hair stands on end when statically charged. The strands are repelling each other!

Why do charges build up in our hair or clothes, but not in other materials? Because insulating materials, like plastic, fabric or glass, will hold charges quite well, while conducting materials, like metals, will not.

Water happens to be an excellent conductor, so in the spring, summer and fall, when the air in Canada holds a lot of moisture, any negative charges built up on your body can jump to the air (or from the air to your body, either way results in a shock) whenever they want. We don’t even notice these numerous small jumps. But in the winter the air is drier, so the charges simply sit on your skin, waiting for you to approach another conductor (like your car or your girlfriend) to leap to freedom.

Read this to hear about why winter air, especially indoors, is so dry!

When thinking of how wet or dry the air is, we tend to only consider humidity. But there’s another metric that’s important: dew point. The dew point is the temperature at which the air is totally saturated with water. When temperatures fall below the dew point, water condenses on solid surfaces, forming dew in the summer, or frost in the winter (hence why the dew point can also be called the frost point). Warmer air can hold more moisture, meaning that when temperatures are low, the dew point and the actual temperature are quite close. Conversely, when temperatures are high, the dew point and actual temperature are far apart.

Why does dew point matter? Because temperature, dew point, and relative humidity (that % you see on your weather app) are closely linked.

As an example, as I’m writing this, the temperature outside is -9 ˚C, and the relative humidity is 57%. Using the chart below, or less confusingly, this online calculator, we can find that the dew point is -16 ˚C. This tells us that if we go outside it won’t feel muggy because the temperature is significantly above the dew point and the air isn’t saturated with water.

However, our furnaces bring that air into our homes and heat it. This doesn’t change the dew point, but it does change the temperature and the relative humidity. What was a relative humidity of 57% at -16 ˚C becomes a relative humidity of only 7% at 20 ˚C. That’s some really dry air.

Now importantly, the only thing changing here is the relative humidity. The absolute humidity is the same since the furnace doesn’t add or remove any moisture when it heats the air. So even though the air inside and outside is equally dry, it feels much dryer inside due to the relative nature of relative humidity. 

Source: https://www.ncbi.nlm.nih.gov/books/NBK143947/

One of the easiest ways to counteract the shocks that come with these Saharan conditions is to run a humidifier. Increasing the relative humidity of your home will allow more charges to dissipate into the air and avoid the shocks that come with letting them build up.  Side note: If you think desert-like is a bit too harsh to describe the indoor conditions in the Canadian winter, think again. The average relative humidity of the Mojave Desert is 28%, a full 21% higher than my house right now. No wonder I have chapped lips. 

If a humidifier isn’t cutting it for you, you could also try swapping out your rubber-soled slippers for ones with leather soles. Since leather is a better conductor than rubber, this will prevent charges from building up to the same degree. Similarly, try to surround yourself with more cotton. As it falls in the middle of the triboelectric series, it doesn’t have much of a tendency to gain or lose electrons, so won’t build charges like wool or fur.  

Still really worried about static shocks? You could always purposefully discharge yourself every once in a while. If you carry a metal object like a coin, key or paper clip around with you, and touch it to something metal in your house, any electrons stuck to your body will flow through the metal and away, preventing the “jumping” effect that causes a shock. 

Last, but not least, you can always rely on anti-static products to take the charge out of your hair and clothes. Dryer sheets contain chemicals like dipalmitoylethyl hydroxyethylmonium methosulfate that release positively charged ions when heated to neutralize the negatively charged electrons on your clothes. You can even rub your hair gently with one to remove static! Anti-static sprays and anti-static guns can also be used to keep static to a minimum wherever you need to, from your favourite dress to your Rubber Soul vinyl. 

Source: http://www.saapedia.org/en/saa/?type=detail&id=4070

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