Start here · Nuclear attackWhere to shelter
Start here · Nuclear attack

Where to shelter

1 min read

The protection factor (PF) says how many times less radiation you get inside than outside: PF 10 = you get 10%. What protects is mass (concrete, brick, earth, water) and distance from the roof, the ground outside and the outer walls.

Protection factor by place Ground level 1–32–310–20≈10≈100Thousands
  • 1–3Inadequate · Outside, a car or a mobile home
  • 2–3Inadequate · Wood-frame house or light one-story building, above ground
  • 10–20Adequate · A house basement
  • ≈10Adequate · Edges or top floor of a large building; multi-story brick or concrete building
  • ≈100Good · Core of a large office building, or its basement
  • ThousandsExcellent · Underground with 3 feet (90 cm) of earth on top

Approximate values from Lawrence Livermore National Laboratory, the technical basis for FEMA's guidance; every building differs. More in protection factor and your home as a shelter.