Chapter 15 · Nuclear and radiological emergency

15.6 Protection factor: which building protects you and where

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The protection factor (PF) tells you how many times less radiation you receive inside than outside. A PF of 10 means you receive 1/10 (10%) of the outdoor dose; a PF of 100, 1/100 (1%). FEMA considers a shelter adequate if it reduces the dose by a factor of 10 or more.

Two things provide protection: mass (concrete, brick, earth, water) and distance from where the fallout settles (roof, surrounding ground, exterior walls). That is why the basement and the center of a large building are the best places, and a middle floor of a tall building is better than the top floor or a ground floor next to the street.

Figure 15.2. Approximate protection factors by building type and location within it. Values from Lawrence Livermore National Laboratory (Buddemeier and Dillon, technical basis of the FEMA guidance). Actual values vary with each building. — **Figure 15.2.** Approximate protection factors by building type and location within it. Values from Lawrence Livermore National Laboratory (Buddemeier and Dillon, technical basis of the FEMA guidance). Actual values vary with each building.

Protection factor: which building protects you and where
Location	Approximate protection factor	Quality
Outdoors, car, mobile home	1 to 3	Inadequate
Wood-frame house, above ground; light one-story building without a basement	2 to 3	Inadequate
House basement	10 to 20	Adequate
Multistory brick or concrete building; edges or top floor of an office building; shallow basement	≈ 10	Adequate
Core of a large office building; basement of a multistory building	≈ 100	Good
Underground with 3 feet (90 cm) of earth on top	Thousands	Excellent

Source of values: Lawrence Livermore National Laboratory, Key Response Planning Factors for the Aftermath of Nuclear Terrorism. These are typical ranges; a specific building can give more or less protection.

How much mass is needed

Each material has a "half-value thickness": the layer that lets through only half of the fallout radiation (PF 2). Two layers give PF 4; three, PF 8; four, PF 16. Values from civil defense material (TACDA/FEMA); other sources give somewhat different figures:

How much mass is needed
Material	Cuts radiation in half with about
Concrete	2.4 in (6 cm)
Packed earth	3.6 in (9 cm)
Water	6 in (15 cm)
Wood	11 in (28 cm)

Bottom line: the wood and drywall of a typical apartment barely slow radiation. Concrete, earth, stored water, and dense objects (tightly packed books, full water jugs) do help, if there is enough of them.