The 30-30 rule for thunderstorm safety is simple: when you hear thunder within 30 seconds of a lightning flash, seek shelter and stay there at least 30 minutes after the last lightning flash.
Start counting as soon as you see a lightning flash and keep counting until you hear the thunder associated with the flash.
Since sound travels at about 5 seconds per mile, a 30-second count means lightning has struck within 6 miles of you. That's within the striking distance of lightning.
If less than 30 seconds elapses between the lightning flash and the sound of its thunder, seek shelter immediately.
The Best Shelter
The best shelter is a sturdy building. A hardtop car is a fair second choice. But small sheds, picnic shelters, baseball dugouts and bleachers don't offer adequate protection from lightning.
Once you've found shelter, remain there until the threat of lightning has passed -- generally 30 minutes. More than half of all lightning deaths occur after the storm has passed.
An important part of lightning safety is to remain aware of weather conditions. While outside, be aware of dark and threatening clouds that may be forming thunderstorms. Being aware will give you more time to seek shelter.
Danger Before the Storm
You may not hear thunder before the storm is close enough to cause damage. Lightning can exit a thunderstorm cloud directly to the ground, or can strike to the side of the cloud long distances away.
Besides the 30-30 rule, there are other lightning safety rules everyone should follow during thunderstorms.
If you're inside, stay away from doors, windows and metal indoor plumbing fixtures and electrical devices.
Electricity from lightning can enter a building along telephone or power lines, television cables or water lines. Avoid taking baths or showers, washing clothes or dishes or using wired telephones or electrical devices such as computers, televisions or stereos.
If You're Outside...
If you're outside, avoid water, open high ground and isolated large trees. Lightning often, but not always, strikes the highest point in the area, so don't let yourself be the highest object around.
If caught on the water, get to shore as quickly as you can. If the watercraft can't make it to shore fast enough, make yourself as low as possible without touching metal.
Swimming or wading in the water during a thunderstorm is very dangerous.
If caught outside, it's best not to huddle together in groups. Individuals should squat several feet apart in low places away from trees and other tall objects.
Shun Lightning Conductor
Don't stand near a tall and isolated lightning conductor, either, since the lightning current can travel through the ground and through water for some distance. Avoid metal, including tractors, fences, golf clubs, towers and antennas.
Don't lean against metal objects such as fences, cars or bicycles, either.
If you see someone hit by lightning, summon emergency aid as soon as possible and go to that person's help as soon as you can.
Help Lightning Victims
Many lightning victims are only stunned or have their hearts temporarily stopped. They can often be saved by the timely application of rescue breathing, CPR or defibrillators. As many as 90 percent of lightning strike victims survive with prompt emergency care.
Following simple lightning safety rules can help ensure that your outdoor activities are safe and worry-free.
More lightning safety guidelines may be found at the National Oceanic and Atmospheric Administration's Lightning Safety Web page (www.lightningsafety.noaa.gov/outdoors.htm).
A web page for lightning safety for children is at www.azstarnet.com/~anubis/sabintro.htm. And the National Lightning Safety Institute Web page is www.lightningsafety.com/ .
(David Emory Stooksbury is associate professor of Biological and Agricultural Engineering at University of Georgia's College of Agricultural and Environmental Sciences.)
(Pam Knox serves as University of Georgia Agricultural Climatologist with UGA Department of Crop and Soil Science.)