We’ve all probably experienced it. The loud POP that goes off when you reach in to touch a metal doorknob on a dry day. There’s a tiny flash of light where your hand had been as you quickly recoil it in reaction to the tingling sensation this zap induces in your hand. It’s all caused by a small spark of the annoying phenomenon known as static electricity.
The spark itself is something you’re likely familiar with. However, what you may not know is that a tiny spark between your hand and a door knob has the potential to release a thousand volts through the air. That’s an extremely high number, and not only because it has three zeroes. It’s also extremely high in comparison with other power sources you may be more acquainted with. Below is a chart that shows the voltage of a number of varying power sources.
You’ve probably learned by now that sticking your finger in a standard outlet isn’t a good idea. If that’s the case, then why isn’t more damage caused by static that creates voltage that is nearly 10x as much? It’s because voltage is not the only consideration when discussing electricity. There are three things that one must consider when looking at the dangers of electric shock.
Voltage (volts) is a quantitative expression of the potential difference in charge between two points in an electrical field.
Resistance (ohms) is the opposition that a substance offers to the flow of electric current. The thicker a substance is that the power is traveling through then the less resistance that exists.
Current (amps) is a flow of electric charge that’s carried by moving electrons.
When talking about electrocution, the voltage necessary is dependent on the current through the body and the duration of the current. Ohm’s Law (Current = the voltage/resistance) states that the current drawn depends on the resistance of the body. Below is a list that discusses how to determine the lethality of electric shock.
- The higher the current, the more likely it is lethal because it has the ability to cause the heart to fibrillate. Since current is proportional to voltage when resistance is fixed (what we just learned about in Ohm’s Law), high voltage does not necessarily mean there is a high current.
- The longer the duration, the more likely it is lethal.
- If the current flows through the heart muscle, it is more likely to be lethal.
- A high voltage level can increase the chances of lethality.
- For high voltage think in terms of 600 or more volts. At this level, the skin can become damage thus reducing the resistance it has. According to the National Institute for Occupational Safety and Health (NIOSH) the resistance of the human body may be as high as 100,000 Ohms. However, wet or broken skin may drop the body’s resistance to only 1,000 Ohms, a remarkable difference. The flow of electricity then becomes much more likely to reach the heart once the skin is damaged depending on the current and the duration.
Based on the above list, the most dangerous part of electricity to the human body is the current. As little as 0.2 Amps can be fatal depending on the person because of its effect on the heart. This is the reason why the much lower voltage of a wall outlet can kill you. The average socket you’d see in a home puts out somewhere between 10 and 20 Amps to power your electronic devices. The typical static electricity you’d encounter when touching a doorknob contains a current that it negligible. That’s why the 1,000 volts caused by the pop when you touch a doorknob doesn’t kill you.
Does that mean that static is harmless?
Not exactly. Mother nature has the ability to create a form of static electricity that can kill you instantly: Lightning. While scientists are still working to confirm their theories regarding lightning’s connection to static electricity, they have a working theory in place as to how clouds become positively charged.
Clouds are made up of billions of tiny particle like ice crystals. These particles rub against one another in the cloud because the clouds are full of big air currents. As these crystals collide with one another, electrons are transferred leading to a positive charge. Often, these charges move from cloud to cloud as the positives and negatives are attracted to one another.
Where as a standard spark of static that escapes your hand onto a household doorknob can contain 1,000 volts, a single bolt of lightning can contain as many as a billion. Even with that much charge, a direct lightning strike doesn’t necessarily guarantee death. In fact, according to LiveScience, approximately 90 percent of those struck by lightning survive the encounter; however, those who survive often suffer from long-lasting neurological damage.
According to the Washington Post, only 3-5% of all deaths and injuries are caused by a direct lightening strike. 50-55% involve ground strikes where the current spreads as far as 60 feet out from contact, and another 30-35% are caused by side splash, an occurrence that causes the bolt to jump from an object or a person to another person.
I recognize static from when I touch a doorknob, but how is lightning the same thing?
To answer that question we need to understand how static electricity is created, and to understand that we need to understand the atom. All physical objects are made up of atoms. Inside an atom are protons, electrons and neutrons. The protons are positively charged, the electrons are negatively charged, and the neutrons are neutral.
In the above example of a Chlorine atom, you can see that its nucleus, the center clump of the image, is made up of protons (+ charge) and neutrons (neutral charge) and is surrounded by a number of electrons (- charge). Electrons and protons attract each other in the atom in order to hold it together. That’s why we say, ‘opposites attract.’ It’s also the reason why atoms are typically balanced with the same number of protons as there are electrons. However, there are times when an atom will actually lose some of its electrons to another atom creating one that is positively charged and one that’s negatively charged. Static exists when there is a build-up of such opposite charges on objects that are separated by something called an insulator. Below is a great video to help explain the process.
These insulators are items that restrict the transference of heat or electricity. Air, itself, is a natural electrical insulator which makes sense when discussing static shock and its transfer between the human body and a door knob. Teflon, paper and glass are also examples of this kind of insulation.
In order to build up charge, a variety of items need to be rubbed together so that they can share electrons between each other. Here are a couple of examples where such charge can is created.
- Your hair and a plastic or rubber comb - Human hair becomes positively (+) charged while the comb becomes negatively (-) charged when used. Since similar charges repel, the hair strands push away from each other, especially if they are very dry. Because the hair and comb now have opposite charges the hair will try to stick onto the comb.
- Skin and polyester clothing - Skin can become positively charged (+) especially when in clothing made of polyester material. That material then becomes negatively charged. When a charged object nears contact with a conductor the charges will jump from a positively charged location until they are able to neutralize the atoms. The drier the skin, the bigger the transfer.
- Clouds and the ground - Cloud to ground lightning occurs when the bottom of the cloud becomes full of negative charge and those charges are attracted to the positively charged ground.
Are there other dangers involved with Static?
There are, because we aren’t the only ones affected by it. Static has the ability to ignite gases and liquids and has been the cause (or in some cases, expected cause) of many fires and explosions across the country and around the world. From gas station fires to chemical plant explosions, it is a real danger with the potential for deadly consequences. Below are some examples of static related accidents.
- A post-earthquake explosion in Alaska is believed to have been caused when a static spark ignited gas from a leaky main that caused a roof to shoot 40-50 feet in the air.
- Static is believed to have ignited a fire in southeast Missouri that ended with ‘nearly 100 explosions’ causing significant damage at an oil distribution company.
- A man filled a propane tank from the bed of his truck causing a static spark that ignited the gas, creating an explosion that caused damage to the business, a pickup truck and its trailer, and injured the business' employees in Redding, CA.
- Static buildup is now credited with the 1937 explosion of the Hindenburg airship. It is believed that water built up over the skin of the vehicle and picked up electric charge during flight. The connection of the landing ropes at the airship’s final destination created a sudden spark as the built up charge sought to escape. It is believed that this spark ignited a small gas leak in the vehicle.
Are there things I can do to reduce the potential risk of these types of rare catastrophes?
Luckily, static is something that you can combat in a number of ways.
- Dry skin can cause the buildup of static, especially in the winter when the air is the driest. Moisturizers can help, but, in many cases, it would require moisturizing all of your body to keep the skin from drying out.
- The type of clothing that’s worn can increase static. As we learned above, Polyester has a tendency to build up charge. Clothing that is 100% cotton can limit your risk.
- There are a number of devices that you can wear in order to reduce the buildup of charge within the body. These devices work to slow the discharge of electrons to help avoid sparks from developing.
- Risk factors can be limited by monitoring the humidity of your home or work space. Static electricity is more active when the air and surrounding materials are dry. As we’ve learned in previous months, humidity is normally much lower in the winter, and using a furnace to stay warm can burn additional moisture out of the air. By using a humidifier you can better control the air moisture levels.
Whichever approach you take, it’s important to remember that these only help reduce the likeliness that an issue will arise. Combining the above list can help you remain even safer than you otherwise may be. Rare as explosions may be, if left unchecked you, your home and your workplace are at risk for serious damage. In the end, that’s the result that could end up being the most shocking.
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