Editing Fallout shelter (section)

=== Shielding ===
A basic fallout shelter consists of shields that reduce gamma ray exposure by a factor of 1000. The required shielding can be accomplished with 10 times the [[Radiation protection#Shielding design|thickness]] of any quantity of material capable of cutting gamma ray exposure in half. Shields that reduce gamma ray intensity by 50% (1/2) include {{convert|1|cm|in|1}} of lead, {{convert|6|cm|in|1|abbr=on}} of concrete, {{convert|9|cm|in|1|abbr=on}} of packed earth or {{convert|150|m|ft|sigfig=1}} of air. When multiple thicknesses are built, the shielding multiplies. Thus, a practical fallout shield is ten halving-thicknesses of packed earth, reducing gamma rays by approximately 1024 times (2<sup>10</sup>).<ref>{{cite web|url=http://www.derose.net/steve/guides/emergency/hardened.html|title=Halving-thickness for various materials|work=The Compass DeRose Guide to Emergency Preparedness&nbsp;– Hardened Shelters|access-date=August 15, 2012|archive-date=January 22, 2018|archive-url=https://web.archive.org/web/20180122235733/http://www.derose.net/steve/guides/emergency/hardened.html|url-status=dead}}</ref>

Usually, an expedient purpose-built fallout shelter is a trench; with a strong roof buried by 1&nbsp;m (3&nbsp;ft) of earth. The two ends of the trench have ramps or entrances at right angles to the trench, so that gamma rays cannot enter (they can travel only in straight lines). To make the overburden waterproof (in case of rain), a plastic sheet may be buried a few inches below the surface and held down with rocks or bricks.<ref name=NWSS6>{{cite book|last=Kearny|first=Cresson H|title=Nuclear War Survival Skills|year=1986|publisher=Oak Ridge National Laboratory|location=Oak Ridge, TN|isbn=0-942487-01-X|pages=37–45|url=http://www.oism.org/nwss/s73p916.htm|quote="The 3-foot thickness of earth shown (or a 2-foot thickness of concrete) will provide an effective barrier, attenuating (absorbing) about 99.9%, of all gamma rays from fallout." "A right-angle turn, either from a vertical or horizontal entry, causes a reduction of about 90%." "...a large piece of 4-mil-thick polyethylene was placed over the mound. This waterproof material served as a "buried roof" after it was covered with more earth."}}</ref>

Blast doors are designed to absorb the shock wave of a nuclear blast, bending and then returning to their original shape.<ref name=lostworlds>{{cite episode|title= Secret U.S. Bunkers|series=[[Lost Worlds (TV series)|Lost Worlds]]|network=The History Channel|date=August 29, 2007|number=18}}</ref>