The last several posts have been about EM radiation hazards (RADHAZ), but there are other electromagnetic hazards. If you’ve ever been shocked by an ESD jumping from your finger to a doorknob after walking across the carpet on a cold dry winters day just imagine that incident being magnified by multiple orders of magnitude. I live in Florida and we are now winding up the season the natives call the 90-90-90 period. That’s 90 days at 90°F, and 90 percent humidity. It rains a lot down here during that time. In fact, in June and July, from about 3:00 p.m., to 5:00 p.m., there is a greater than 20 percent chance that we are having a thunderstorm, whereas prior to 11:00 a.m. any day of the year there will be less than a 1 percent chance of rain. September and October bring the most hurricanes.
The mornings may start out beautiful, but the weather can change quickly. It can go from golf weather to a thunderstorm in 15 – 20 minutes . . . and let me tell you, when we are having a thunderstorm, we are having lightning! There are places around the world with more lightning than Florida, but we are the lightning capital of the US, with more than 100 thunderstorm days per year.
The problem is: the people enjoying the theme parks, and the anglers, the boaters, the roofers, the golfers, the gardeners, and everyone else enjoying the beautiful weather just don’t want to quit. They wait until the very last minute to give up what they are doing and seek shelter. Often that’s too late. Florida has the most lightning injuries and deaths in the US and it can sneak up on you. The storm doesn’t have to be overhead, hammering you with hail, and drowning you with rain at two or three inches per hour. Lightning can strike 25 miles away from the leading edge of the storm.
The good thing about hearing the thunder is that means you are still alive, since the lightning flash creates the thunder. Plus, the thunder produced by the strike generally provides adequate warning to prompt us to seek shelter, if we follow the NOAA 30/30 flash-bang rule. This rule is based on the fact that sound travels about 1100 feet/second and, if the time between seeing a flash of lightning and hearing the associated thunder is less than 30 seconds, you are within about a six mile strike zone and need to find shelter.
If you are outside and the flash-bang is nearly simultaneous, run for shelter while the cloud is recharging. You don’t have much time. If there’s no shelter, find a low spot or depression, keep your feet together, keep your head lowered, hunker down as low as possible, and don’t touch the ground with your hands. This position reduces the chance of being struck and the severity of lightning injury if you are. With luck, you may live through being struck, but if at all possible do plan for and find shelter fast. Don’t lie down on the ground! Lightning ground current spreading away from the strike location can kill you. Once in a sheltered location, remain there for at least 30 minutes after the last sound of thunder, just to be on the safe side.
Your car—or anyone else’s for that matter—makes a reasonably good lightning shelter provided the car body is metal and the windows are closed. Just be sure you aren’t in contact with any metal surfaces. The metal envelope of the car acts as a leaky RF shielded enclosure and also provides a lightning path around you to ground. There is a mistaken belief that the rubber tires protect the occupants. Not so! Lightning just jumped thousands of feet from the cloud to the car. A few inches of rubber won’t even slow it down.
If you are in Florida, or anywhere there is lightning, here’s a brief reminder list of safety recommendations.
If you are outside:
• Seek immediate shelter
• Get out of—or off of—the water. This also includes indoor pools.
• Get off the beach
• Don’t stand near isolated tall structures such as light poles or trees
• Keep away from metal objects such as bicycles, golf carts, umbrellas, fences, etc.
• Don’t use open pavilions or huts for shelter. Get in a car, or go inside a substantial structure. Open pavilions or other small open shelters work OK for rain but not for lightning.
If you are inside:
• Stay away from doors, windows, and fireplaces. Most fireplaces have chimneys that extend above the roof.
• Shut down and unplug your computer and other sensitive electronic devices well ahead of the storm. Don’t touch the electric cords during the storm. Consider installing transient suppressors even though they may not always protect the devices.
• Stay away from bathroom/kitchen sinks and fixtures. These things often have roof vents and metal plumbing.
• If you need to make a phone call, use your cell or wireless phone, not a land line.
Although lightning often strikes the same place multiple times, especially if it’s tall/high, I want to end this post with the following lightning quote by Willie Tyler. He indicates that lightning makes major changes in the things it strikes and we don’t want it to be us.
The reason lightning doesn’t strike twice in the same place is that the same place isn’t there the second time. ~Willie Tyler, comedian