A nuclear explosion nearby: what to do in the first hour

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Checked against official guidance (NHS, St John Ambulance, the Drinking Water Inspectorate and the UK Chief Medical Officers) on 2 November 2026. Not a substitute for a first-aid course.

Do this now

1. Don't look at the flash. Turn away and close your eyes.
2. Outside? Get down. Take cover behind something solid, or lie face down with skin covered, until the blast wave has passed.
3. Get inside within about 10 minutes. Nearest solid building. Basement or middle of the building, away from windows.
4. Shut it up. Close windows and doors. Turn off fans, extractor fans and anything that pulls in outside air.
5. Clean off. If you were outside: outer clothes off, into a bag, then wash with soap and water. No hair conditioner.
6. Stay in for at least 24 hours. Leave only for a fire, collapse or medical emergency, or if officials tell you to.
7. Tune in. Battery or wind-up radio, Emergency Alerts, GOV.UK.

First, what official advice exists

The UK's public advice for radiation is UKHSA's "go in, stay in, tune in". It is written for radiation emergencies such as accidents. There is no separate public UK leaflet for a nuclear explosion, and the UKHSA page does not describe a flash or a blast wave.

The most detailed official advice on a nuclear explosion comes from the US: Ready.gov, and FEMA's Planning Guidance for Response to a Nuclear Detonation (third edition, 2022). FEMA's guide is written for emergency planners, not households, but its public message is the same as the UK's: get inside, stay inside, stay tuned. We use UKHSA first and the US and Swedish guides only where the UK says nothing. Where we quote FEMA's figures, they come from US planning studies, not a promise of what would happen here.

Second 0: the flash

• Don't look. FEMA's guidance says the flash can cause temporary flash blindness more than 10 miles away. It lasts several seconds in daylight and can last 5 to 10 minutes at night. Looking straight at the fireball can cause permanent eye damage, though this is much rarer.
• If you're driving, expect to be dazzled and expect crashes ahead. Stop as soon as it's safe. FEMA warns flash blindness is likely to cause road accidents and blocked roads far from the damage.

The first minute: the blast wave

• Get down. Ready.gov says take cover behind anything that offers protection, or lie face down to protect bare skin. Sweden's brochure says lie down, preferably in a small pit or ditch.
• Indoors? Get away from windows straight away and drop behind something solid. FEMA's guide lists flying glass and debris among the causes of injury.
• Stay down until the blast wave has passed, then move.

Minutes 1 to 10: get into the best shelter you can reach

Ready.gov says you should have 10 minutes or more before fallout arrives. FEMA's guidance gives the same figure. Fallout is radioactive dust and sand-like particles that fall from the cloud. Being under thick walls and floors cuts how much radiation reaches you.

Best to worst (FEMA pages 65 to 67, Ready.gov):

Brick, stone, concrete and earth block radiation well. Wood, plasterboard and thin metal block little, but FEMA says many layers add up, so a room in the middle of the house with several walls around it is better than a room on an outside wall. The building doesn't need to be airtight to protect you from fallout, and FEMA says a building with minor damage can still be used if it's structurally sound.

Don't travel home if you're elsewhere. UKHSA says stay in the nearest building, not your home.

Minutes 10 to 60: shut it up and clean off

Close up the building. UKHSA says close outside doors, windows and vents, including trickle vents, and turn off fans and air conditioning. Ready.gov adds forced-air heating and fireplace dampers. Finland says seal gaps with tape or cling film and switch off mechanical ventilation.

Clean off if you were outside. UKHSA and Ready.gov give the same steps:

1. Take off your outer layer of clothing carefully, without shaking it. UKHSA says this can remove around 90% of contamination. Keep your hands away from your eyes, nose and mouth (Ready.gov).
2. Put the clothes in a bag and leave the bag away from people and pets.
3. Shower or wash with soap or a mild shampoo. Don't use conditioner: UKHSA says it can bind contamination to hair.
4. Can't wash? Wipe bare skin and hair with a clean wet cloth. Ready.gov says don't use household cleaning wipes or hand sanitiser.
5. Pets that were outside: wash with soap or shampoo and water, wearing gloves if you have them (UKHSA).

Why the first hour matters. FEMA's guidance says fallout gives off over half of its energy in the first hour, then keeps decaying fast. Being well inside during that hour is the single most useful thing you can do. Ready.gov sums up the idea as time, distance and shielding.

If you're in a poor shelter

FEMA's planning guidance has one rule for people in poor shelter, such as a car or a small wooden building. If a much better shelter is within about 15 minutes' travel, people in very poor shelter should move to it within 30 minutes of the explosion. People in slightly better shelter can wait an hour or two before moving. This is US planning advice. Follow any instructions you get from the authorities first.

Injuries

• Bleeding: the NHS says press on the wound with a clean pad or folded cloth and raise it if you can. If something such as glass is stuck in it, don't pull it out and don't press on it: press firmly on either side. Add more pads on top if blood soaks through. Call 999 if it won't stop, if blood spurts, or if something is stuck in the wound.
• Burns: the NHS says cool the burn under cool running water for 20 minutes. If there's no running water, use cool bottled water or a wet towel. Then cover it loosely with cling film. Call 999 or go to A&E for a very large or deep burn, a burn on the face, genitals or bottom, or a burn from chemicals or electricity. Don't use creams, butter or plasters.

Hour 1 onwards: stay in and tune in

• How long: Ready.gov says at least 24 hours. FEMA says at least 12 to 24 hours. UKHSA, for radiation emergencies, says one to two days, possibly longer. To be cautious, plan for the longest of these unless officials say otherwise.
• When to leave early: only for a fire, the building collapsing, a medical emergency or another immediate danger, or if officials tell you to go (Ready.gov, FEMA).
• Don't collect children. UKHSA says schools and nurseries will keep children inside until it's safe.
• Food and water: UKHSA says food and drink that were indoors, including tap water, are safe. Wipe sealed containers from outside with a damp cloth before opening (Ready.gov). See food and water after fallout.
• Iodine tablets: only if officials tell you to, and only tablets they provide (UKHSA).

Printable checklist: the first hour

Flash and blast

• Don't look. Turn away, eyes shut
• Outside: take cover or lie face down, skin covered
• Indoors: away from windows, down behind something solid
• Driving: stop when safe; expect dazzle and crashes

Within about 10 minutes

• Nearest solid building, not home
• Basement or middle of the building, most walls between you and outside
• Not a car

Within the hour

• Windows, doors, trickle vents shut. Fans and extractors off
• Outer clothes off, into a bag, bag away from people
• Wash with soap or mild shampoo. No conditioner
• Pets in and washed
• Bleeding: press, raise, 999 if it won't stop
• Burns: cool water 20 minutes, cling film

Then

• Radio on. Emergency Alerts on
• Stay in at least 24 hours unless fire, collapse or officials say otherwise
• Don't fetch children from school
• Iodine only if officials say, and only tablets they provide

What official advice doesn't cover

• Distances from a blast. Effects depend on the weapon, the height of the burst and the weather. We don't give distance tables or say which places are at risk.
• A UK-specific nuclear explosion leaflet. There isn't a public one. UKHSA's radiation guidance and the US guides agree on the steps above.
• Older advice. Nuclear War Survival Skills (1979, updated 1987) is a US Cold War civil defence book. It talks about shelter stays of up to two weeks. Today's official advice talks about 24 to 48 hours first, with officials then deciding who should move. Read the old book as history, not today's instructions.

No guide can promise safety. Every official source we checked gives the same order: don't look, get down, get inside fast, get to the middle, clean off, stay in and listen.

Related guides

• Radiation emergency in the UK: what official advice says (go in, stay in, tune in)
• UK Emergency Alerts: a calm guide
• Worried about war? How UK households can prepare — calmly
• Home first aid kit and medicine cabinet: a UK checklist

We're an independent UK site, not the government. We check guides against official sources and link to them. In an emergency call 999.

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