30-30 Rule

When you see lightning, count the time until you hear its thunder. If this time is 30 seconds or less, lightning is already a threat and you should be inside. Be sure to allow enough time to find a safe location from lightning. If you can't see the lightning, just hearing the thunder is a good back-up rule. Wait 30 minutes or more after hearing the last thunder before going outside. Safer Locations: while no place offers 100% guaranteed safety against lightning, some places are definitely safer than others. Seek a safer location when required. Don't hesitate, seek shelter immediately! The lightning casualty stories are full of events where people were about to make it to safety when they were struck; if they'd just started a minute earlier, they'd have been safe. The best shelter commonly available against lightning is a large fully enclosed building with wiring and plumbing, e.g. a typical house. Once inside, stay away from any conducting path to the outside. Stay off corded telephones. Stay away from electrical appliances, lighting, and electric sockets. Stay away from plumbing. Don't watch lightning from windows or doorways. In large buildings, inner rooms are generally better. If you can't get to a house, a vehicle with a solid metal roof and metal sides is a reasonable second choice. As with a house, avoid contact with conducting paths going outside: close the windows, lean away from the door, put your hands in your lap, don't touch the steering wheel, ignition, gear shifter, or radio. Convertibles, cars with fiberglass or plastic shells, and open framed vehicles don't count as lightning shelters.