Lightning is a powerful electrical discharge that forms inside thunderstorms and can travel between clouds or from a cloud to the ground. It matters because lightning can strike miles away from heavy rain and can injure people who are outdoors in open areas, near tall objects, or in water. Knowing what to do before, during, and after a storm helps students protect themselves at sports fields, parks, bus stops, and school events.
Lightning safety is part earth science and part emergency preparedness.
Key Facts
- If thunder is heard, lightning is close enough to be dangerous.
- 30-30 rule: seek shelter if the time between lightning and thunder is 30 s or less, and wait 30 min after the last thunder before going outside.
- Distance to lightning in miles ≈ seconds between flash and thunder ÷ 5.
- Distance to lightning in kilometers ≈ seconds between flash and thunder ÷ 3.
- Safe shelters include fully enclosed buildings and hard-topped vehicles with windows closed.
- Avoid open fields, isolated trees, metal fences, water, and high ground during a thunderstorm.
Vocabulary
- Lightning
- Lightning is a sudden electrical discharge caused by the buildup of electric charge in a storm cloud or between a cloud and the ground.
- Thunder
- Thunder is the sound made when lightning rapidly heats the air and causes it to expand explosively.
- Storm cell
- A storm cell is a region of a thunderstorm where strong rising air, clouds, precipitation, and lightning can develop.
- Ground current
- Ground current is electrical energy that spreads through the ground after lightning strikes nearby and can injure people standing in the area.
- Shelter
- Shelter is a safe enclosed place, such as a building or hard-topped vehicle, that helps protect people from lightning.
Common Mistakes to Avoid
- Staying outside until rain begins is wrong because lightning can strike before rain reaches your location.
- Standing under a lone tree is wrong because tall isolated objects are more likely to be struck and can send current through the ground or side flash to a person.
- Thinking a picnic shelter or dugout is safe is wrong because open-sided structures do not fully protect you from lightning current.
- Returning to the field right after the last visible flash is wrong because lightning can still occur after a storm seems to be moving away, so wait 30 minutes after the last thunder.
Practice Questions
- 1 You see lightning and hear thunder 15 seconds later. Estimate the distance to the lightning in miles and decide whether you should seek shelter.
- 2 At a soccer practice, the last thunder was heard at 4:12 p.m. Using the 30-minute rule, what is the earliest time students should return to the field?
- 3 A group is in a park when thunder is heard, and the closest options are a tall tree, an open picnic shelter, a metal fence, and a school building 2 minutes away. Explain which option is safest and why.