All About Lightning

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Wildfires in the American West continue to rage, with September and October expected to be no better. Although most wildfires are caused by humans, lightning strikes have been identified as the culprits for some of this year’s biggest conflagrations.  In the San Francisco Bay area alone, three “lightning complex” fires have burned over 800,000 acres of woodland. More than 13,000 lighting strikes have been recorded since mid-August in California alone.

Many of us associate lightning with rainstorms, but “dry” lightning appears to be involved in causing the latest fires. Certain storms produce thunder and lightning without any appreciable rain as moisture evaporates before reaching the ground. These are not uncommon in drier areas of the country.


A Lightning “bolt” is a discharge of a large amount of electricity in the atmosphere or between the atmosphere and the ground. Air normally acts to insulate the positive and negative charges in clouds. At one point, however, the difference between the two is so great that electricity is generated and released.

Most lightning events occur high in the atmosphere within a cloud or from cloud-to-cloud. Cloud-to-ground strikes are more responsible for injuries to humans. In recent years, the National Oceanic and Atmospheric Administration (NOAA) has reported dozens of annual lightning strike fatalities. Although the death rate from a lightning strike hovers around 10 percent, the grand majority of survivors suffer some form of lasting ill effect.

(Aside: Why doesn’t lightning strike airplanes? Actually, it does. Commercial aircraft are designed so that electricity travels through them without any interruption. They are usually struck without experiencing damage.)


Thunder is the sound caused by nearby lightning as it passes through the air. The discharge heats the air to as high as 50,000 degrees Fahrenheit for a fraction of second, causing air to rapidly expand and then contract. This produces a sound wave that we hear as thunder.

(Aside: The temperature of a bolt of lightning reaches several times that of the surface of the sun!)

When you listen to thunder, the first rumble is created by the part of the lightning channel closest to you. Continued rumbling comes from portions of the lightning that are farther away.

Can you tell how far away a lightning strike is? If you hear a cracking or a very loud booming sound, that means the lightning was very close. More of a rumble, it’s probably several miles away. To hear thunder at all, the flash should be within 10 miles.

As the speed of sound is about 343 meters per second, a space of 5 seconds between a flash and associated thunder equals about a mile. Count the number of seconds and divide by 5 to calculate the distance to the strike.

(Aside: Two of Santa’s reindeer, Donner and Blitzen, are named after the German words for thunder and lightning.)


There are a number of ways in which a person may be “struck by lightning”:

Direct Strikes: A person struck directly by a lightning bolt is usually out in the open. The electricity moves along the skin and also through the body’s cardiovascular or nervous systems. Burns occur on the skin, but cardiac arrest from the current in the body is more likely to cause death.

Ground Strike: When lightning strikes, say, a tree, energy travels outward along the ground. This is known as “ground current”. Anyone near a lightning strike could be a victim. Indeed, this form of lightning strike causes the most injuries and deaths.

Side Strike: More commonly known as a “side flash”, it occurs when lightning strikes a taller object (again, say, a tree) near the victim. Some of the current jumps from the original target of the strike to the victim, who is usually a very short distance away. This is why you shouldn’t take cover under a tree.

Conduction Strike: Lightning can travel (or be “conducted”) along long distances in wires or other metal surfaces that help provide a path for it to travel. If you’re in contact with a wire fence and lightning strikes some distance away, you might be affected. Inside, anything (or anyone) connected to wiring, plumbing, or other metal surface may serve as a conductor.

Streamer Strike: “Streamers” aren’t as common a cause of a lightning injury but are still dangerous. As the downward-moving electrical charge (called the “step leader”) approaches the ground, electrical streamers are produced that rise from ground-based objects (even a person). If a person is involved, they could be killed or injured even if the streamer didn’t connect with the step leader itself.


Being struck by lightning can be lethal, but effects vary based on the amount of current traveling through the body. You may see:

  • Cardiac Arrest or Irregular Beat Patterns (arrythmias)
  • Respiratory Arrest/Lung Inflammation
  • Ruptured Eardrums/Deafness
  • Eye Damage/Blindness
  • Burns
  • Mental Changes (memory, sleep disorders)
  • Nerve Damage (numbness, pain)
  • Broken Bones
  • Internal Bleeding
  • Chronic Vertigo
  • Coma

Distinctive branching scars caused by blood vessel damage known as “Lichtenberg figures” can form as a result of blood vessel damage.


When thunder roars, go indoors! It’s important to realize that being outside is dangerous when a thunderstorm is in progress. If you can hear thunder, you are in danger of being hit by lightning for up to 30 minutes after the last rumble.

Get inside a sturdy building or a metal-topped vehicle (windows up) as quickly as possible. Strive to avoid being the tallest object in the area. Even when there are taller objects, like trees or utility poles, stay away from them. Lightning will likely target them, especially if they are isolated. Avoid touching metal: It doesn’t attract lightning, but conducts it for 100 feet or more.

Once inside, stay off computers and other electrical equipment. Avoid touching plumbing like sinks and faucets. Stay away from doors, windows, and porches. Don’t lean again anything metal or concrete. Lightning can travel through any metal wiring or bars that may be inside concrete walls or flooring.

Cardiac arrest is the most common immediate cause of death.  The victim needs first aid immediately. Call for help and begin CPR. If an Automatic External Defibrillator is available, use it. Get the victim into a building if possible; lightning can strike twice in the same place.


If thunderstorms are in the forecast, postpone your outside activities. There are circumstances, however, where you may be caught outside and unprepared for a lightning storm. In these cases:

  • Leave high ground like ridges or hills.
  • Don’t take cover under isolated trees. If you’re in the middle of the forest, stay near lower trees.
  • Avoid rocky overhangs or cave entrances as shelters. someone at the entrance may form a conduit between the cave roof and floor. The same thing goes for the covered porch of a house.
  • Stay away from lakes, streams, or other bodies of water.
  • Avoid lying flat on the ground, but stay low with as little of your body touching the ground as possible (see below).
  • Don’t touch barbed wire fences, power lines, or anything else that conducts electricity.

If you’re in a group, some say to stay 10 feet apart. This actually may make an individual more prone to being struck, but lessens the likelihood of multiple casualties and increases the chance of having uninjured rescuers at hand.

Hearing about a person struck by lightning may be shocking, but not as much as if you were the victim. Be prepared and make wise choices whenever there’s electrical activity in your area.


Joe Alton MD

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