The best place to shelter from nuclear fallout
The best place to shelter from nuclear fallout is underground, or in the centre of a large multi-storey brick or concrete building, away from the roof and outside walls. If you can't reach either within about 10 minutes, go into any building: even a poor shelter is far better than staying outside.
This page is general information, not official advice; instructions from your local authorities always come first.
Why do some places protect better than others?
Fallout settles on the ground, on roofs and on window ledges, and gives off radiation, mainly gamma rays. That radiation is reduced by mass, such as brick, concrete, earth and water, and by distance from where the particles have settled.
Experts measure this with a protection factor: the radiation dose outside divided by the dose inside. A protection factor of 10 means you receive one-tenth of the outdoor dose.
How much does each place protect you?
These figures come from Lawrence Livermore National Laboratory research used in US federal planning.
| Location | Protection factor | Verdict |
|---|---|---|
| Car or other vehicle | 1.7 to 2 | Inadequate |
| Wood-frame house, ground floor, no basement | 2 to 3 | Inadequate, but far better than outside |
| Basement of a house | 10 to 20 | Adequate |
| Multi-storey apartment building, lower floors | about 10 | Adequate |
| Multi-storey building, middle floors, centre | up to 100 | Good |
| Core of a large office building, or basement of a multi-storey building | about 100 | Good |
| Underground with 3 ft (1 m) of earth above, subway, deep parking garage | hundreds to thousands | Best |
Which shelter should I choose in the moment?
Go down this list and take the first option you can reach within about 10 minutes, before fallout is likely to arrive:
- An underground space, such as a subway station, underground parking garage or building basement.
- The centre of a large, multi-storey brick or concrete building, away from the roof and ground-floor windows.
- The basement of a house.
- The innermost room on the lowest floor of any building, such as a bathroom, closet or hallway with no outside walls.
- Any building at all.
- Only if no building can be reached, a ditch, culvert or the lowest ground available, with your face covered. Move to a building as soon as you can.
Don't hunt for the perfect shelter. In the first minutes, time outside matters more than shelter quality.
Where should I sit inside the building?
Get as far as you can from both the roof and the ground outside, with as many walls as possible between you and the open air.
- Basement: the corner or area most below ground level, away from windows and window wells.
- Tall building: the centre of the building on a middle floor. Avoid the top two floors and the ground floor. Stairwells and interior corridors are often good.
- House with no basement: the most central ground-floor room, away from outside walls. Stay low.
How can I make a shelter better?
Once you are inside and safe, add mass between you and the outside. Dense materials work best. This tip comes from the civil-defence manual Nuclear War Survival Skills.
- Push heavy furniture, bookcases or full filing cabinets against the walls that face outside.
- Stack books, filled water containers or boxes of soil around your spot and, if possible, above it.
- Sit or lie on the floor, which puts more of the building between you and fallout on the ground.
Use only what is already in the building. Don't go outside to collect materials.
Then close windows, doors and fireplace dampers, and turn off fans, air conditioning and heating that draws in outside air.
Should I move to a better shelter?
Official guidance is to stay where you are for at least 24 hours, unless there is an immediate danger or officials tell you to move.
The Livermore research notes one exception. If you are in a very poor shelter, such as a car, a mobile home or a single-storey wooden building with no basement, and a much better one is only a few minutes away, moving can reduce your total dose. The best time is before fallout arrives. After that, move only if officials advise it or there is an immediate hazard.
For what comes next, see how long to stay inside after nuclear fallout and the full timeline for surviving a nuclear attack.
Sources
- Lawrence Livermore National Laboratory: Key Response Planning Factors for the Aftermath of Nuclear Terrorism
- Ready.gov: Radiation Emergencies
- CDC: What to Do - Get Inside
- FEMA: Planning Guidance for Response to a Nuclear Detonation, 3rd edition
Questions
Is a basement safe from nuclear fallout?
A house basement gives a protection factor of about 10 to 20, meaning you receive roughly a tenth to a twentieth of the outdoor dose. Researchers class that as adequate shelter. The basement of a multi-storey building is better still, at about 100.
Is a car a safe place to shelter from fallout?
No. A vehicle has a protection factor of only 1.7 to 2, so it halves your radiation dose at best. Official guidance is to get out and into a building. Stay in a car only as a last resort when no building can be reached.
Which floor of a tall building is safest from fallout?
A middle floor, in the centre of the building. Fallout settles on the roof and on the ground, so avoid the top two floors and the ground floor. A basement or underground parking level is also a good choice.
Do broken windows make a building useless as a shelter?
No. FEMA's planning guidance says buildings with broken windows can still give adequate protection from the radiation coming from fallout on the ground.
