Lightning Safety

Lightning kills on average about 20 people a year in the United States and injures hundreds more, many with lifelong nerve damage, memory problems, and chronic pain. Deaths have fallen sharply, from well over 100 a year in the mid-twentieth century, because more people work indoors and because public education works. The single most important message: no place outdoors is safe when a thunderstorm is nearby.

How Close Does Lightning Have to Be to Be Dangerous?

If you can hear Thunder, you are close enough to be struck. Lightning can reach 10 miles or more from the storm that produced it, sometimes striking out of clear blue sky ahead of the rain. These "bolts from the blue" are one reason victims are often caught off guard.

The 30-minute rule exists because the back side of a storm can still produce strikes as it moves away, and a significant share of lightning deaths happen before the rain starts or after it ends.

Is the 30-30 Lightning Rule Still Used?

For years people were taught the "30-30 rule": seek shelter if the time between flash and thunder is 30 seconds or less (about 6 miles). The National Weather Service no longer promotes the first half of that rule. Counting requires you to see the flash and match it to the right thunder, which is hard with multiple strikes, and it encourages people to wait until a storm is already close. The simpler rule is better: if you can hear thunder at all, go indoors. The second "30," waiting 30 minutes after the last thunder, is still recommended.

Where Is Safe During a Lightning Storm?

• A substantial building: one with plumbing and electrical wiring, such as a home, school, office, or store. The wiring and pipes carry current into the ground around you if the building is struck.
• A hard-topped metal vehicle with the windows closed: a car, truck, or bus. The metal body conducts current around the occupants and into the ground. The tires offer no protection; the metal shell does the work.

These are not safe:

• Picnic shelters, dugouts, tents, bus stops, porches, and open garages.
• Convertibles, golf carts, motorcycles, and bicycles.
• Under trees of any size.

Is It Safe to Shower During a Thunderstorm?

Lightning can still hurt you inside a building through the wiring and plumbing:

• Avoid corded phones and plugged-in electronics such as desktop computers and gaming consoles. Cell phones and cordless phones are safe to use.
• Stay out of the shower and bath, and avoid washing dishes.
• Stay away from windows, doors, and porches.
• Do not lie on concrete floors or lean on concrete walls, which may contain metal reinforcement.

How Does Lightning Hurt People?

Only a small fraction of victims receive a direct strike. Most are hurt in other ways:

• Ground Current: current spreading through the ground from a nearby strike. It causes the most injuries and kills many livestock.
• Side Flash: current jumps from a struck tree or object to a person nearby.
• Conduction: current travels through wires, fences, or metal pipes to someone touching them. It is the main cause of indoor lightning injuries.
• Upward streamers: the person is part of a streamer that did not connect to the main channel but still carried current.
• Direct strike: the person is the path of the Cloud-To-Ground Lightning flash. It is the least common but most often fatal.

Myths

• "Lightning never strikes the same place twice." It often does. The Empire State Building is struck about 20 to 25 times a year.
• "Rubber tires protect you in a car." It is the metal body, not the tires.
• "If it is not raining, you are safe." Lightning can strike 10 miles or more from the rain.
• "Lightning victims are electrified and should not be touched." The human body does not store charge. Touch them and help immediately.
• "Crouching makes you safe." The old "lightning crouch" is a last resort that only slightly reduces risk. There is no safe place outdoors.

What to Do If You Are Caught Outside in a Lightning Storm

If you truly cannot reach shelter, lower your risk (it will never be zero):

• Get off elevated areas such as hills, ridges, and peaks.
• Never lie flat on the ground; that increases exposure to ground current.
• Never shelter under an isolated tree.
• Stay away from water, wet items, and metal objects such as fences and power lines.
• If in a group, spread out so one strike does not injure everyone.

Outdoor activities such as fishing, camping, boating, beach trips, and sports account for a large share of deaths. Check the forecast before you go, and plan how you will reach shelter.