Editing Bunker (section)

==Design==
<gallery mode="packed">
File:Hill 60 illowra battery port kembla.jpg|Inside the [[Illowra Battery|Hill 60 Bunker]], Port Kembla, New South Wales, Australia. One of many [[Template:Barracks Batteries Bunkers and Forts in Sydney|bunkers south of Sydney]]
File:Project-131-tunnel-door-9791.jpg|In a [[Underground Project 131|Project 131]] tunnel under the hills of [[Hubei]]
File:Objekt 17 5001 toegangsdeur 02.JPG|Object 17/5001 Prenden, Germany
File:Harparskog Line Bunker 2.jpg|Bunker of the Harparskog Line in [[Raseborg]], Finland
File:Used_Bunker_in_Singapore.jpg|Bunker in [[Singapore]]
File:Maginot line 1.jpg|The entrance to [[Ouvrage Schoenenbourg]] along the [[Maginot Line]] in France.
File:Albania bunkers.jpg|[[Bunkers in Albania]]
File:German single person bunker.JPG|German single person bunker for reconnaissance personnel in the field
File:Brandenburg_Kirchmoeser_bunker.jpg|Bunker of type Winkel in [[Brandenburg an der Havel]]
File:Possum_Park_Bunker_8a.jpeg|Munitions bunker at [[Possum Park]], Queensland, Australia.
File:Gravel_Gertie_-_PANTEX_Plant_-_1981.jpg|[[Gravel Gertie]] at the [[Pantex]] nuclear weapons plant, Amarillo, Texas. 
File:Bunker 2.jpg|[[Austria-Hungary|Austrian]] bunker from World War I in [[West Ukraine]]
</gallery>

===Blast protection===
Bunkers deflect the blast wave from nearby [[explosion]]s to prevent ear and internal injuries to people sheltering in the bunker. While frame buildings collapse from as little as {{cvt|3|psi|kPa psi bar|lk=on|order=out}} of [[overpressure]], bunkers are regularly constructed to survive over {{cvt|10|bar|kPa psi bar|order=out}}. This substantially decreases the likelihood that a [[bomb]] (other than a [[bunker buster]]) can harm the structure.

The basic plan is to provide a structure that is very strong in [[compression (physical)|physical compression]]. The most common purpose-built structure is a buried, steel [[reinforced concrete]] [[Vault (architecture)|vault]] or [[arch]]. Most expedient blast shelters are civil engineering structures that contain large, buried tubes or pipes such as sewage or rapid transit tunnels. Improvised purpose-built blast shelters normally use earthen arches or vaults. To form these, a narrow, {{convert|1|-|2|m|ft|round=0.5|adj=on}}, flexible tent of thin wood is placed in a deep trench, and then covered with cloth or plastic, and then covered with {{convert|1|-|2|m|ft|round=0.5|abbr=in}} of tamped earth.

A large ground shock can move the walls of a bunker several centimeters in a few milliseconds. Bunkers designed for large ground shocks must have sprung internal buildings to protect inhabitants from the walls and floors.<ref>{{cite web|url=http://prepare-and-protect.net/2014/01/bunker-thoughts/|title=Bunker Thoughts|date=25 January 2014|website=prepare-and-protect.net|access-date=2 May 2018|url-status=live|archive-url=https://web.archive.org/web/20170930193410/http://prepare-and-protect.net/2014/01/bunker-thoughts/|archive-date=30 September 2017}}</ref>

===Nuclear protection===
{{See also|Fallout shelter}}

Nuclear bunkers must also cope with the underpressure that lasts for several seconds after the [[shock wave]] passes, and block [[radiation]]. Usually, these features are easy to provide. The overburden ([[soil]]) and structure provide substantial radiation shielding, and the negative pressure is usually only {{frac|1|3}} of the overpressure.<ref>The Survival Option: Guide to Living Through Nuclear War, Ivan Tyrrell. Publisher: Jonathan Cape Ltd; 1st Edition (1982), Language: English, Hardcover: 256 pages, {{ISBN|0224020595}}</ref>

===General features===
[[File:PanoBunker.jpg|thumb|250px|right|A bunker on the island of [[Texel]], in the Netherlands.]]
The doors must be at least as strong as the walls. The usual design is now starting to incorporate [[vault door]]s. To reduce the weight, the door is normally constructed of steel, with a fitted steel lintel and frame. Very thick wood also serves and is more resistant to heat because it chars rather than melts.{{Citation needed|date=December 2008}} If the door is on the surface and will be exposed to the blast wave, the edge of the door is normally counter-sunk in the frame so that the blast wave or a reflection cannot lift the edge. A bunker should have two doors. Door shafts may double as ventilation shafts to reduce digging.

In bunkers inhabited for prolonged periods, large amounts of [[ventilation (architecture)|ventilation]] or [[air conditioning]] must be provided in order to prevent ill effects of heat. In bunkers designed for war-time use, manually operated ventilators must be provided because supplies of electricity or gas are unreliable. One of the most efficient manual ventilator designs is the [[Kearny Air Pump]]. Ventilation openings in a bunker must be protected by [[blast valve]]s. A blast valve is closed by a shock wave, but otherwise remains open. One form of expedient blast valve is worn flat rubber [[tire]] treads nailed or bolted to frames strong enough to resist the maximum overpressure.<ref>{{cite web |url=http://www.oism.org/nwss/s73p939.htm |title=App. D: Expedient Blast Shelters |publisher=Arnold Jagt |access-date=2010-06-10 |url-status=live |archive-url=https://web.archive.org/web/20110525040356/http://www.oism.org/nwss/s73p939.htm |archive-date=25 May 2011}}</ref>