Lightning: When to Go Inside and When It Is Safe to Come Out

Direct answer: if you can hear thunder, you are close enough to be struck. Go inside a substantial building or a hard-topped vehicle. Stay there until 30 minutes after the last thunder you hear — not after the rain stops, not after the sky clears. Most lightning deaths happen to people who went out too early or waited too long to go in.

Why thunder is the whole rule

Lightning and thunder leave at the same moment; light arrives instantly and sound takes about three seconds per kilometre. Hearing thunder at all means the discharge was within roughly 15 kilometres, and that is inside the range at which a storm can put a strike on the ground near you.

This is why the advice is not “go in when the storm arrives”. Strikes reach well ahead of the rain, and out of a sky that from where you stand still looks acceptable. People describe being hit “out of nowhere”; from the storm's point of view they were always within reach.

There is no useful counting rule for deciding to stay out. Counting the gap between flash and bang tells you how far away that strike was. It tells you nothing about where the next one will be.

What actually counts as shelter

Only two things reliably protect you, and both work for the same reason — they give the current a path that is not through your body.

• A substantial, enclosed building with wiring and plumbing. The metal in the walls carries the current to ground around you.
• A fully enclosed, hard-topped vehicle, with the windows up and your hands off metal. The shell does the work, not the tyres.

These do not protect you, and each one has a death record behind it:

• Open-sided picnic shelters, bus stops, dugouts, verandas and carports.
• Tents and any temporary structure, whatever it is made of.
• Trees. Sheltering under one is one of the most consistently fatal choices in this subject, because current that strikes a tree spreads outward through the ground.
• Convertibles, open cabs, motorbikes and bicycles.

Inside is safer, not automatically safe

Roughly a third of lightning injuries happen indoors, because the current that a building conducts to ground travels along the things you may be touching.

• Do not use a corded phone or plug-in device. Mobile phones and battery devices are fine.
• Stay off plumbing — no showers, no washing up, no baths.
• Keep away from windows, doors and any exterior wall.
• Do not lean on concrete walls or lie on a concrete floor; both usually contain metal reinforcement.

The 30 minutes after are the dangerous part

The last strike of a storm is frequently a long way from its rain, and it can come from the anvil cloud spreading ahead of or behind the core — a strike out of a sky that has already begun to clear. This is why the rule is counted from the last thunder, not from the last raindrop.

The count restarts every time you hear thunder again. Thirty minutes with no thunder is the end; twenty-five minutes and one distant rumble is not.

Sports bodies and outdoor employers build their rules on exactly this, and it is the part people skip, because by then the weather looks finished and the match, the shift or the walk home is waiting.

If you are caught outside with nowhere to go

Be honest about this: there is no safe position outdoors. What follows reduces risk and does not remove it, and the only real answer is to have gone in earlier.

• Keep moving toward a real building or vehicle. Do not stop to wait it out under something.
• Get off high ground and away from isolated tall objects. Leave open water immediately.
• Put down anything long and conductive — poles, umbrellas, tools.
• If you are in a group, spread out so a single strike cannot injure everyone.
• The old advice to crouch in a ball is no longer recommended by major agencies: it does not meaningfully protect you, and it keeps you outside longer.

Someone has been struck

They carry no charge. It is safe to touch them immediately, and the belief that it is not has cost lives during the minutes that matter most.

Call emergency services. Lightning most often kills by stopping the heart, so start CPR if there is no breathing or pulse and continue until help arrives. People do survive lightning strikes, and survival is closely tied to how quickly resuscitation begins.

Why no warning tells you this

A severe thunderstorm warning is issued on measured criteria — hail size and wind speed — and lightning is not one of them. Every thunderstorm produces lightning, which means an ordinary storm carrying no warning at all can kill you, and a severe warning tells you nothing extra about that specific risk.

That is not a flaw in the warning. It is a limit of what it was built to say, and it is exactly why the thunder rule exists: it does not depend on anyone having issued anything.

How this site fits

Thunderstorm warnings shown here come from the national agencies that issue them, published with their own severity and a link to the original. We do not detect lightning and we do not issue warnings. For the guidance above, the source is your own national weather service and the safety agencies linked below.

Related reading: what a severe thunderstorm warning actually measures, and why an app and an official warning are not the same thing.

Frequently asked questions

How far away is lightning if I can hear thunder?

Within roughly 15 kilometres, which is close enough to be struck. Thunder is audible only from a strike near enough to reach you, so hearing it at all is the signal to go inside. Counting the gap between flash and bang tells you where that strike was, not where the next one will be.

How long should I wait before going back outside?

Thirty minutes after the last thunder you hear, not after the rain stops. The count restarts every time thunder returns. Strikes come from the spreading anvil cloud well after the rain has passed, out of a sky that already looks clear.

Is a car safe in a thunderstorm?

A fully enclosed hard-topped vehicle is reasonably safe, with the windows up and your hands off metal surfaces. The metal shell carries the current around you - the tyres have nothing to do with it. Convertibles, open cabs and motorbikes offer no protection.

Is it safe to touch someone who has been struck by lightning?

Yes, immediately. A person struck by lightning carries no electrical charge. Call emergency services and begin CPR if they are not breathing - lightning most often kills by stopping the heart, and survival depends heavily on how quickly resuscitation starts.

Sources

• US National Weather Service - Lightning Safety
• NWS - Lightning Safety When Working Outdoors
• US CDC - Lightning Safety Tips and Resources

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