Lightning is a rapid, powerful natural electrical discharge that occurs between a cloud and the ground or within a cloud itself. This atmospheric event generates immense heat, often reaching temperatures up to 50,000 degrees Fahrenheit, alongside currents that can peak at tens of thousands of amperes. The intensity of a strike makes it an immediate and severe threat to life and property. Understanding the warning signs and taking decisive, protective action is the most effective way to protect yourself during a thunderstorm.
Recognizing the Warning Signs
The sound of thunder confirms that you are within striking distance of a lightning discharge, making immediate action necessary. Lightning can strike as far as 10 miles away from where rain is falling, meaning the absence of precipitation does not indicate safety. The most practical metric for judging proximity and when to seek shelter is the “30/30 Rule.”
The first “30” in this rule refers to the seconds counted between seeing a flash of lightning and hearing the resulting thunder. Since sound travels significantly slower than light, this time interval can be used to estimate the storm’s distance; every five seconds indicates roughly one mile of separation. If that count is 30 seconds or less, the storm is close enough that you must seek a safe, enclosed structure immediately.
The second “30” dictates the time you should remain in that safe location after the storm appears to have passed. Wait 30 minutes after the last clap of thunder is heard before resuming any outdoor activity. This waiting period is necessary because thunderstorms can produce trailing strikes or distant discharges that still pose a threat.
Identifying Primary Safe Locations
The highest level of protection is found inside a fully enclosed, substantial building that contains plumbing and electrical wiring. These elements provide a dedicated, grounded pathway for the electrical charge to travel safely into the earth, preventing the charge from passing through occupants. Structures like sheds, carports, tents, or open-air gazebos are unsafe because they lack the necessary grounding and enclosure to divert the electrical energy.
A hard-topped, fully enclosed vehicle with a metal body also offers a high degree of safety. The metal shell of the car functions similarly to a partial Faraday cage, a structure that channels electrical current around the exterior of the enclosure. If the vehicle is struck, the electrical current flows over the metal surface and is directed to the ground, leaving the interior largely unaffected.
It is a misunderstanding that rubber tires protect the occupants; the immense voltage of a lightning strike easily jumps the gap between the wheel and the ground. To maintain safety within a vehicle, all windows must be closed. Occupants should also avoid touching any metal components, such as door handles, the steering wheel, or the radio. Vehicles with fiberglass bodies or open tops, such as convertibles, do not provide this protective channeling effect.
Mitigation When Shelter Is Impossible
When a safe building or metal vehicle cannot be reached, such as when hiking or boating, risk reduction strategies become the only option. The first step is to quickly move away from high ground, isolated tall objects like trees or utility poles, and bodies of water. These locations and objects are far more likely to be struck and can create dangerous side flashes or ground current pathways.
If you are caught in an open area, you must assume the “lightning crouch” position as a last resort to minimize your contact with the ground. This posture involves crouching low to the ground with your feet together, placing your hands over your ears, and tucking your head down. The goal is to make yourself the lowest possible target and to reduce the area of contact with the ground.
Keeping your feet close together limits the danger of ground current, which spreads outward from the strike point. If current enters your body, having your feet together allows it to travel up one leg and down the other, bypassing the heart and vital organs. Lying flat on the ground is dangerous because it maximizes your body’s contact with the earth, increasing the risk of severe injury from ground current.
Avoiding Risks Inside a Building
Being inside a house or structure significantly lowers the risk of injury, but it does not remove the danger entirely. Lightning that strikes a building can travel along conductive pathways, including the electrical wiring, phone lines, and plumbing system. It is important to stay away from anything that provides a direct path for the electrical current to enter your space.
Avoid contact with water sources, as lightning can travel through metal plumbing pipes. Activities like showering, bathing, or washing dishes should be avoided until the storm has passed. Do not use corded electronic equipment, such as landline phones or plugged-in computers, as the charge can travel through the electrical system.
Even concrete floors and walls can pose a risk because they often contain metal reinforcement, known as rebar, which acts as a conductor. Do not lie down on concrete floors or lean against concrete walls during a storm. Staying away from doors and windows is also recommended, as metal components in these openings can conduct the electrical charge indoors.