Geoscience Reference
In-Depth Information
en hours and will decay about 90 percent more over the next forty-eight hours (leaving only 1
percent of the original level of radioactivity), making it relatively safe for you to leave your
place of shelter and seek a location outside of the contaminated zone. If you have the good for-
tune to have access to a true fallout shelter with adequate food, water, its own independent
power source, and a HEPA-type air-filtration system, your safest course of action is to stay put
for two weeks, at which point the gamma radiation will have subsided to roughly one-thou-
sandth of what it was originally (Deyo 2006, 389).
Dense materials, such as earth, stone, concrete, and water, will provide the best shielding
from gamma radiation emitted by freshly fallen radioactive fallout. For every 3.6 inches (9 cm)
of packed earth, gamma radiation is cut by a factor of two. According to FEMA, the minimal
recommended makeshift fallout shelter shielding is provided by the following equivalents: 5 to
6 inches (13 to 15 cm) of bricks; 7 inches (18 cm) of earth; 8 inches (20 cm) of hollow concrete
blocks; 10 inches (25 cm) of water; 14 inches (35 cm) of topics or magazines; or 18 inches (45
cm) of wood (Deyo 2006, 401). The more shielding the better.
For quick shelter inside existing buildings, a basement location is usually best, provided
that air circulation is minimized to prevent the circulation of fallout into your shelter from out-
side. In general, the basement locations that will receive the fewest gamma rays will be sitting
crouched against an earth-protected wall to minimize the “angle of incidence” exposure to
gamma rays entering through the more marginal radiation shielding provided by walls and ceil-
ings that don't have an outer layer of packed earth (Kearny 1999). See
figure 17-2
for the best
locations for minimizing your exposure to radiation from fallout, when sheltering inside an ex-
isting building.
