We’ve had two 90-degree days here at the office. There is contention about whether the heat is good or bad. I personally like it. I think riding a bike on a nice hot day is one of the best things ever, especially if you can jump in a river or lake afterwards. This hot weather hopefully signifies that summer is either here or quickly approaching, and that means that we should start experiencing thunderstorms soon. With that in mind, I thought I’d take some time to refresh you all on what lightning is as well as safety precautions for both you and your electronics.
Lightning itself, the bright bolts you actually see, are discharges of static electricity. Technically speaking lightning itself has no temperature because lightning is moving electrical charges, which have no temperature. But flowing charges (also called current) can heat up the medium through which they travel. The more resistance, the more heating. Air is a poor conductor, so current flowing through it generates a lot of heat. The bolts you see are actually air being turned into plasma, and it is very hot. How hot? It’s actually hotter than the sun. The plasma can reach around 30,000 K or 53,000 F. The surface of the sun is “only” 6,000 K. In fact despite the high voltages and current involved with lightning, humans are most at risk from electrical burns. Death from electrical shock usually only occurs when the current through the body is between 0.1 and 0.2 amps. Lightning is going to generate far more current than that. These kinds of shocks aren’t generally fatal because the muscular contractions are so severe that the heart is forcibly clamped shut thereby protecting it from ventricular fibrillation (the mechanism that actually causes death from electricity). However, such current may result in severe burns.
In terms of protecting yourself from lightning, the best thing to do is get indoors if at all possible. You may have heard that a car is also a safe place with respect to lightning. This is true, but there are some caveats. First, why is the car a safe place? If you took the average car, and stripped away all the plastics and materials, you’d basically see a metal shell. It’s this shell that ultimately protects you by acting as a Faraday cage. The current is absorbed and dissipated by the frame of the car. Sometimes, depending on conditions, the lightning will actually jump the rubber tires and go into the ground. This would make your car more like a grounded Faraday cage, but grounding isn’t necessary for it to work. Obviously a car isn’t a perfect Faraday cage, so precautions should still be taken to maximize your protection. You should stop the car, shut it off and roll up all the windows. You should then rest your hands on your lap and not touch anything else in the car.
What about electronics and appliances? When I was a little kid, my dad had a police scanner and my mom got him a big external antenna for it. We mounted the antenna on the roof of our house, and I remember that we then drove a long rod into the ground and connected it to another rod atop the antenna. My dad explained it to me back then that this was so if lightning wanted to strike, it would hit the rod and be directed down into the ground safely, rather than into the house, or into his scanner equipment. We never got struck by lightning there, but I do remember helping him install it.
You’ve likely seen lightning rods on any tall structure, but you’re less likely to have used or installed one yourself. For protection of home electronics, we often use lightning arresters, also called surge protectors. These simple but effective devices are very cool. They’re usually placed where wires enter a structure. Normally the relatively low voltage power flows from the wires outside to the inside through the arrester. There is a secondary channel in the arrester that has a very high resistance, so normal electricity won’t flow through it, but lighting will be high enough voltage to cause that channel to conduct. This channel is typically routed to ground. So the lightning, or surge, will come in on the wires, but then be redirected away from the sensitive equipment inside the structure. The difference between a lightning arrester and a lightning rod is that the rod is meant to absorb, or even attract, a direct strike. The arrester only deals with the high voltage once it has entered the power grid or telecommunication network.
As always though, it’s important to remember that no protection mechanism is 100% failsafe. Especially when dealing with very high energy things like lightning, the strategy is generally deflect and redirect rather than suppress and neutralize. The only failsafe method to protect your electronics from lightning is to unplug them completely.
Bonus tidbit: Now that you know a little bit more about the composition and nature of lightning, I can more easily explain what causes the thunder that follows. The current of the strike so instantaneously superheats the air into plasma that it expands explosively, causing the thunder we hear.