Editing Effects of nuclear explosions (section)

=== Blast damage ===
[[File: Blastcurves psi.svg|thumb|right|Overpressure ranges from 1 to 50 [[Pounds per square inch|psi]] (6.9 to 345 kilopascals) of a 1 kiloton of TNT air burst as a function of burst height. The thin black curve indicates the optimum burst height for a given ground range. Military planners prefer to maximize the range at which 10 psi, or more, is extended over when attacking civilian targets, thus a 220 m height of burst would be preferred for a 1 kiloton blast. To find the optimum height of burst for any weapon yield, the cube root of the yield in kilotons is multiplied by the ideal H.O.B for a 1&nbsp;kt blast, e.g. the optimum height of burst for a 500&nbsp;kt weapon is ~1745 m.<ref>{{cite book |editor1-first=Samuel |editor1-last=Glasstone |editor2-first=Philip J. |editor2-last=Dolan |title=The Effects of Nuclear Weapons |date=1977 |publisher=U.S. Department of Defense |isbn=978-0-318-20369-0 |doi=10.2172/6852629 |osti=6852629 |url=https://digital.library.unt.edu/ark:/67531/metadc1197666/ }}{{page needed|date=August 2023}}</ref>]]
[[File: Abombdamage1945.svg|thumb|left|An estimate of the size of the damage caused by the 16&nbsp;kt and 21&nbsp;kt [[atomic bombings of Hiroshima and Nagasaki]].]]

The high temperatures and radiation cause gas to move outward radially in a thin, dense shell called "the hydrodynamic front". The front acts like a piston that pushes against and compresses the surrounding medium to make a spherically expanding [[shock wave]]. At first, this shock wave is inside the surface of the developing fireball, which is created in a volume of air heated by the explosion's "soft" X-rays. Within a fraction of a second, the dense shock front obscures the fireball and continues to move past it, expanding outwards and free from the fireball, causing a reduction of light emanating from a nuclear [[detonation]]. Eventually the shock wave dissipates to the point where the light becomes visible again giving rise to the characteristic '''double flash''' caused by the shock wave–fireball interaction.<ref>{{cite web|url=http://www.nuclearweaponarchive.org/Russia/TsarBomba.html|title=The Soviet Weapons Program – The Tsar Bomba|website=www.nuclearweaponarchive.org|access-date=30 March 2018}}</ref> It is this unique feature of nuclear explosions that is exploited when verifying that an atmospheric nuclear explosion has occurred and not simply a large conventional explosion, with [[radiometer]] instruments known as [[Bhangmeter]]s capable of determining the nature of explosions.

For [[air burst]]s at or near sea level, 50–60% of the explosion's energy goes into the [[blast wave]], depending on the size and the [[Nuclear weapon yield|yield of the bomb]]. As a general rule, the blast fraction is higher for low yield weapons. Furthermore, it decreases at high altitudes because there is less air mass to absorb radiation energy and convert it into a blast. This effect is most important for altitudes above 30&nbsp;km, corresponding to less than 1 percent of sea-level air density.

The effects of a moderate rain storm during an [[Operation Castle]] nuclear explosion were found to dampen, or reduce, peak pressure levels by approximately 15% at all ranges.<ref name="afswp1">{{cite web|url=https://archive.org/details/MilitaryEffectsStudiesonOperationCastle1954|title=Military Effects Studies on Operation CASTLE|last=AFSWP|date=30 March 2018|access-date=30 March 2018|via=Internet Archive}}</ref>

[[File: General Effects of Atomic Bomb on Hiroshima and Nagasaki.ogv|thumb|left|"The General Effects of the Atomic Bombs on Hiroshima and Nagasaki." Describes effects, particularly blast effects, and the response of various types of structures to the weapons' effects]]

Much of the destruction caused by a nuclear explosion is from blast effects. Most buildings, except reinforced or blast-resistant structures, will suffer moderate damage when subjected to overpressures of only 35.5 [[kilopascals]] (kPa) (5.15 [[pounds-force per square inch]] or 0.35 atm). Data obtained from Japanese surveys following the [[atomic bombings of Hiroshima and Nagasaki]] found that {{convert|8|psi|kPa|abbr=on}} was sufficient to destroy all wooden and brick residential structures. This can reasonably be defined as the pressure capable of producing severe damage.<ref name="afswp1"/>

The blast wind at sea level may exceed {{cvt|1000|km/h|mph m/s|sigfig=1}}, approaching the [[speed of sound]] in air. The range for blast effects increases with the explosive yield of the weapon and also depends on the burst altitude. Contrary to what might be expected from geometry, the blast range is not maximal for surface or low altitude blasts but increases with altitude up to an "optimum burst altitude" and then decreases rapidly for higher altitudes. This is caused by the nonlinear behavior of shock waves. When the blast wave from an air burst reaches the ground it is reflected. Below a certain reflection angle, the reflected wave and the direct wave merge and form a reinforced horizontal wave, known as the '"[[Mach stem]]" and is a form of [[constructive interference]].<ref>{{cite web|url=http://www.atomicarchive.com/Effects/effects6.shtml|title=The Mach Stem – Effects of Nuclear Weapons |website=www.atomicarchive.com|access-date=30 March 2018}}</ref><ref>{{cite web | url=https://www.fas.org/nuke/intro/nuke/blast.htm | title=Striving for a Safer World Since 1945}}</ref><ref>http://www.atomicarchive.com/Movies/machstem.shtml video of the Mach 'Y' stem, it is not a phenomenon unique to nuclear explosions, conventional explosions also produce it.</ref> This phenomenon is responsible for the bumps or 'knees' in the above overpressure range graph.

For each goal overpressure, there is a certain optimum burst height at which the blast range is maximized over ground targets. In a typical air burst, where the blast range is maximized to produce the greatest range of severe damage, i.e. the greatest range that ~{{convert|10|psi|kPa|abbr=on}} of pressure is extended over, is a GR/ground range of 0.4&nbsp;km for 1&nbsp;[[kiloton]] (kt) of TNT yield; 1.9&nbsp;km for 100&nbsp;kt; and 8.6&nbsp;km for 10 [[megatons]] (Mt) of TNT. The optimum height of burst to maximize this desired severe ground range destruction for a 1&nbsp;kt bomb is 0.22&nbsp;km; for 100&nbsp;kt, 1&nbsp;km; and for 10&nbsp;Mt, 4.7&nbsp;km.

Two distinct, simultaneous phenomena are associated with the [[blast wave]] in the air:

* '''Static [[overpressure]]''', i.e., the sharp increase in pressure exerted by the shock wave. The overpressure at any given point is directly proportional to the density of the air in the wave.
* '''[[Dynamic pressure]]s''', i.e., drag exerted by the blast winds required to form the blast wave. These winds push, tumble and tear objects.

Most of the material damage caused by a nuclear air burst is caused by a combination of the high static overpressures and the blast winds. The long compression of the blast wave weakens structures, which are then torn apart by the blast winds. The compression, vacuum and drag phases together may last several seconds or longer, and exert forces many times greater than the strongest [[hurricane]].

Acting on the human body, the shock waves cause pressure waves through the tissues. These waves mostly damage junctions between tissues of different densities (bone and muscle) or the interface between tissue and air. Lungs and the [[abdominal cavity]], which contain air, are particularly injured. The damage causes severe [[hemorrhaging]] or [[air embolism]]s, either of which can be rapidly fatal. The overpressure estimated to damage lungs is about 70 kPa. Some [[eardrum]]s would probably rupture around 22 kPa (0.2 atm) and half would rupture between 90 and 130 kPa (0.9 to 1.2 atm).