Nuclear detonation and the first protective actions

A nuclear detonation can cause a flash, intense heat, blast, debris and radiation. Radioactive fallout can affect areas away from the explosion. No household action can guarantee survival close to a detonation, but taking shelter promptly can reduce exposure for people who survive the immediate effects.

If a warning arrives before any explosion: Follow its instructions immediately. Seek the nearest substantial, safe building or the shelter identified by authorities. Do not spend warning time driving across town to collect relatives or searching for an ideal bunker. Move away from windows. Keep essentials only if they are immediately at hand.

If you see a sudden intense flash: Do not look towards it. Turn away, protect your eyes and get low behind available protection. The US CDC's supplementary blast guidance advises lying face down until the heat and blast waves have passed. If indoors, stay away from glass and protect yourself from falling objects. Move to safer shelter when you can do so without entering fire or collapse hazards.

After the immediate blast danger

1. Get indoors promptly. A brick or concrete building provides more protection than a car or tent.
2. Use a basement or central part of a substantial building where it is safe, away from external walls and windows.
3. Close external doors, windows and vents where possible and switch off fans and air conditioning as described by UKHSA. Do not disable safety-critical ventilation or essential life-support equipment.
4. If you have been outside in affected conditions, follow radiation decontamination advice in Removing radioactive contamination from clothing and skin. Do not postpone entering shelter to shower outside.
5. Listen for UK and local official instructions. Keep children, dependants and pets with you where they already are.

A building on fire, collapsing or filling with dangerous fumes is not a safe place to remain. Move to safer nearby shelter by the safest available route and request help. Otherwise, avoid unnecessary movement outside. Do not travel to collect children during a sheltering instruction; their school or nursery should follow its emergency arrangements.

Authority note: UKHSA provides the core UK radiation response. The immediate flash and blast details above are supplementary US CDC guidance, not a claim that the UK has issued a bespoke instruction for this event.