All thunderstorms produce lightning in varying amounts, either an occasional flash or continuously. Most lightning stays within the clouds, but it becomes a safety problem when CG (Cloud to Ground) flashes occur. It only takes one CG flash to injure, kill or cause a fire.
Lightning is electricity that moves toward ground. The human body contains salty water, which conducts electricity better than air, so the body may present a conduit for the lightning to reach the ground.
At the first sign of lightning, immediately get out and off the water and seek shelter. Swimming pools, both indoor and outdoor, have underground pipes, gas lines and wires that connect to a wide area, so lightning strikes that hit elsewhere can travel to the pool. Seek shelter inside a building or fully enclosed vehicle with the windows up. If possible, avoid seeking shelter under a canopy, picnic or rain shelter.
Pools and beaches should remain cleared for 30 minutes after the last observed lightning strike or audible thunder clap.
If indoors , avoid water, and stay away from doors and windows. Do not use the telephone. Take off headsets. Turn off, unplug, and stay away from appliances, computers, power tools and TV sets. Because water may travel through and on pipes and tubing, lightning may strike exterior electric and phone lines that lead to shocks in indoor equipment.
If caught in the open during a thunderstorm, take steps to minimize your risk:
- Avoid being the tallest object around. Seek the best shelter you can find in clumps of shrubs or trees of uniform height, ditches, trenches or the low ground. Get as low as you can, but squat down -- don't lie prone on the ground. Put your feet together.
- Avoid being less than 15 feet from other people. This will allow the current to go to ground more easily, making it less likely for multiple people to be injured.
- Stay away from the tallest object around, such as an isolated tree. Taking shelter from the rain under an isolated tree is hazardous. At high altitudes, seeking shelter among depressions in the rock or shallow caves will not offer much protection from lightning on a mountaintop. Your best protection is to get down from the peaks as quickly as possible. Leave your gear behind. You can always go back and retrieve your gear after the storm passes.
- Contrary to myth, there is no reliable "warning sign" that lightning is about to strike. For instance, your hair may not stand on end. The first sign of a CG may be the flash itself. Of course, if your hair does stand on end, take steps to protect yourself immediately.
- Plan your evacuation and safety measures in advance . Lightning often precedes rain, so don't wait for the rain to begin before suspending activities.
- "If you can see it (lightning), flee it (take shelter). If you can hear it (thunder), clear it (suspend outdoor activities)." There is no safe distance from a thunderstorm. CG flashes occasionally jump out of a thunderstorm and strike the ground miles away. So if you can see lightning, you are under threat.
- The time from the flash to the thunder roughly equates to the distance the lightning is from you. If you see a flash, count the seconds from the time of the flash to the thunder; Five seconds corresponds to about a mile. Follow the "30-30 Rule": Take shelter if the time from seeing a flash until the time you hear thunder is 30 seconds or less, and do not resume activities until 30 minutes have elapsed from the last lightning and thunder.
- Lightning does not have to hit you directly to injure you. It can travel along the ground and can jump from nearby objects.
- Stay away from fences and power lines that lead into areas where lightning is occurring. An electrical charge can travel along the wires and jump to you or cause an injury if you touch live wires or an energized fence.
- Keep away from metal objects, such as machinery, motors and power tools. They might conduct current.
- Avoid contact with two separate metal or wet objects; your body could serve as an electrical conduit between them.
If someone is struck by lightning, get medical help immediately! Lightning victims do not retain an electric charge and are safe to handle. While waiting for help, administer CPR to any victims if their heart and/or breathing has stopped. Cover the victims and do not move them. If they are conscious, reassure them and try to keep them calm. Eighty percent of victims survive the shock of a non-direct lightning strike. Common lightning after-effects include impaired eyesight and loss of hearing. Electrical burns should be treated in the same way as other burns.