Where to shelter from fallout, and for how long

An ordinary building protects you enormously from fallout. That is not a hunch: protection is measured as a dose reduction factor, and the difference between standing in the street and sitting in the centre of a concrete basement is counted in factors of tens or hundreds. The question is which building, which part, and for how long.

The two factors that decide

Mass. The more material between you and the particles — concrete, brick, earth — the less radiation reaches you. That is why the basement wins: it has earth around it and a floor slab above.

Distance. Material falls on horizontal surfaces: roofs, streets, terraces, yards. The further you are from those, the better. That is why the middle floors of a tall building are excellent: they are far from the roof and far from the ground at the same time.

Place	Protection	Why
Centre of a concrete basement	Maximum	Earth around and a slab above
Underground car park, metro	Maximum	Buried and high mass
Middle floors of a tall building	Very high	Far from the roof and the street
Interior room of a masonry house	Medium	Walls all round, no windows
Ground floor next to the street	Low	The street is covered in material
Top floor or under the roof	Very low	The roof is the most contaminated part
Prefab home, caravan, car	Almost none	Very little mass

Inside the building: position yourself well

1. Go down or find the centre. Move away from external walls, windows and the roof.
2. Put things between you and the outside. Bookshelves full of books, wardrobes, mattresses propped against the street-facing wall: it all adds mass.
3. Close doors and windows and turn off mechanical ventilation, same as in a nuclear accident.
4. Keep the sleeping area away from the bag of contaminated clothing and from the front door.
5. If the building has a shared basement, tell the neighbours: a shared basement protects ten people as well as it protects one.

The 24 hours: what you do in them

• Check the radio at intervals. Coming out is staggered by zone, and that is the only way you will hear it.
• Eat and drink what was sealed. Fridge, tins, bottled water.
• Send text messages, never calls: they get through when the network is saturated.
• Do not burn anything. No candles, no camping stoves, no gas heaters, no generator in an attached garage.
• Organise waste from the start: a lidded bucket and bags. Within 24 hours with no running water, this stops being a detail.
• Keep children occupied. Boredom and fear push people to look out of windows, and that is the behaviour to avoid.

When and how you come out

Coming out is ordered by the authorities and is usually zone by zone and in phases. When it comes:

1. Cover your skin the first time out: long sleeves, a hat, a mask if you have one.
2. Do not raise dust. No dry sweeping, no shaking out rugs, no leaf blowers.
3. Go to the agreed meeting point, not house to house looking for people.
4. Go through decontamination checks if there are any: that is where it is actually measured whether you are carrying material.
5. Follow the instructions on water and food even if everything looks normal.

What to do in the minutes before all of this is in the first 15 minutes, and how to clean up on the way in is in radiological decontamination. To work out how much water and food to keep stored, the kit calculator gives quantities by people and days.