A clap of thunder and a blinding flash of lightning jolted my back deck early this morning. The sound and light were so close I expected to see charred grass in the backyard.
With a scheduled morning run, I considered whether running outdoors in a thunderstorm was safe.
The answer is clearly no, but not for the reason you might think.
Running or being outdoors during a thunderstorm brings the risk of being struck by lightning. The elementary school adage, “When Thunder Roars, Go Indoors,” applies well to our adult selves. The clever logic in this phrase is synching action to thunder, not lightning. If you can hear thunder, then lightning is in the area.
The odds of being struck directly by lightning are very low, about one in a million , with about 30 reported deaths yearly. Most people have the sense to stay in indoors during lightning storms. Farm animals are a different story. A University of Wisconsin study found that 100,000 farm animals are killed by lightning each year. The real danger is not from a direct lightning strike but from the ground current.
When lightning strikes the ground, it fuses dirt and clay into silicas called glass rock in the shape of a twisted tube. This process dissipates the electric current from lightning but is not instantaneous or localized. Lightning that strikes the ground has been shown to travel up to 60 feet from the point of impact. If a person or farm animal is near a ground strike of lightning, you can be shocked. The electric current will travel up one leg through the body, possibly affecting the heart and breathing, and then out the other leg back into the ground.
Farm and wild animals unknowingly increase their risk for lightning by gathering under trees during a storm. Trees are tall and are filled with water, which can attract lightning. Lightning traveling down a tree trunk turns this water into steam. The rapidly expanding team can explode the bark and limbs clear off the tree trunk. The charge carried by the lightning flows into the earth, where it is eventually dissipated, but not before affecting objects in its path.
Get indoors or back in a car immediately if you are caught outside running during a thunderstorm. Avoid sheltering under trees or near metal and water, as these all attract lightning. If there is no shelter available, get low. You want to be the lowest thing around. A ditch or depression is a good place to hunker down. You want to minimize your contact with the ground—crouch low on the balls of your feet. Allow your heel to touch. You are minimizing your ground contact to reduce the probability of ground current reaching you. If it does reach you, touching your heels together increases the chance that lightning will enter one foot and leave the other instead of traveling through your body.
When thunder roars, get indoors! Other than that, let’s chase those running goals.