Editing Effects of nuclear explosions (section)

== Direct effects ==

=== 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).

=== Thermal radiation ===
[[File:342-usaf-11034 Medical Aspects-Hiroshima.webm|thumb|left|Silent USSBS ([[United States Strategic Bombing Survey]]) footage which is primarily an analysis of flash burn injuries to those at Hiroshima. At 2:00, as is typical of the shapes of sunburns, the protection afforded by clothing, in this case, pants, with the nurse pointing to the line of demarcation where the pants begin to completely protect the lower body from burns. At 4:27 it can be deduced from the burning shape that the man was facing the fireball and was wearing a vest at the time of the explosion etc. Many of the burn injuries exhibit raised [[keloid]] healing patterns. 25 female survivors required extensive post-war surgeries and were termed the [[Hiroshima maidens]].]]
Nuclear weapons emit large amounts of [[thermal radiation]] as visible, infrared, and ultraviolet light, to which the atmosphere is largely transparent. This is known as "flash".<ref name="Nuclear Bomb Effects">{{cite web|title=Nuclear Bomb Effects|url=http://www.solcomhouse.com/nuclearholocaust.htm|work=The Atomic Archive|publisher=solcomhouse.com|access-date=12 September 2011|archive-url=https://web.archive.org/web/20110827052819/http://www.solcomhouse.com/nuclearholocaust.htm|archive-date=27 August 2011|url-status=dead}}</ref> The chief hazards are burns and eye injuries. On clear days, these injuries can occur well beyond blast ranges, depending on weapon yield.<ref name="remm.nlm.gov"/> Fires may also be started by the initial thermal radiation, but the following high winds due to the blast wave may put out almost all such fires, unless the yield is very high where the range of thermal effects vastly outranges blast effects, as observed from explosions in the multi-megaton range.<ref name="remm.nlm.gov"/> This is because the intensity of the blast effects drops off with the third power of distance from the explosion, while the intensity of radiation effects drops off with the second power of distance. This results in the range of thermal effects increasing markedly more than blast range as higher and higher device yields are detonated.<ref name="remm.nlm.gov"/>

Thermal radiation accounts for between 35 and 45% of the energy released in the explosion, depending on the yield of the device. In urban areas, the extinguishing of fires ignited by thermal radiation may matter little, as in a surprise attack fires may also be started by blast-effect-induced electrical shorts, gas pilot lights, overturned stoves, and other ignition sources, as was the case in the breakfast-time bombing of Hiroshima.<ref name="osti.gov">{{cite journal|url=http://www.osti.gov/bridge/product.biblio.jsp?osti_id=4421057|title=Medical Effects Of Atomic Bombs The Report Of The Joint Commission For The Investigation Of The Effects Of The Atomic Bomb In Japan Volume 1|first1=A. W.|last1=Oughterson|first2=G. V.|last2=LeRoy|first3=A. A.|last3=Liebow|first4=E. C.|last4=Hammond|first5=H. L.|last5=Barnett|first6=J. D.|last6=Rosenbaum|first7=B. A.|last7=Schneider|date=19 April 1951|website=osti.gov|access-date=30 March 2018|doi=10.2172/4421057|doi-access=free|osti=4421057 }}</ref> Whether or not these secondary fires will in turn be snuffed out as modern noncombustible brick and concrete buildings collapse in on themselves from the same blast wave is uncertain, not least of which, because of the masking effect of modern city landscapes on thermal and blast transmission are continually examined.<ref>{{cite web |url=http://www.usuhs.mil/afrrianniversary/events/rcsymposium/pdf/Millage.pdf |title=Modeling the Effects of Nuclear Weapons in an Urban Setting |archive-url=https://web.archive.org/web/20110706161001/http://www.usuhs.mil/afrrianniversary/events/rcsymposium/pdf/Millage.pdf |archive-date=6 July 2011 | date=6 July 2011 }}</ref> When combustible frame buildings were blown down in Hiroshima and Nagasaki, they did not burn as rapidly as they would have done had they remained standing. The noncombustible debris produced by the blast frequently covered and prevented the burning of combustible material.<ref>[https://www.fourmilab.ch/etexts/www/effects/eonw_7.pdf Glasstone & Dolan (1977) Thermal effects Chapter] p. 26</ref>[[File: The patient's skin is burned in a pattern corresponding to the dark portions of a kimono - NARA - 519686.jpg|right|thumb|upright|Burns visible on a woman in Hiroshima during the blast. Darker colors of her [[kimono]] at the time of detonation correspond to clearly visible burns on the skin which touched parts of the garment exposed to thermal radiation. Since kimono are not form-fitting attire, some parts not directly touching her skin are visible as breaks in the pattern, and the tighter-fitting areas approaching the waistline have a much more well-defined pattern.]]

There are two types of eye injuries from thermal radiation: [[flash blindness]] and [[Retina|retinal burn]]. Flash blindness  is caused by the initial brilliant flash of light produced by the nuclear detonation. More light energy is received on the retina than can be tolerated but less than is required for irreversible injury. The retina is particularly susceptible to visible and short wavelength infrared light since this part of the [[electromagnetic spectrum]] is focused by the lens on the retina. The result is bleaching of the visual pigments and temporary blindness for up to 40 minutes. A retinal burn resulting in permanent damage from scarring is also caused by the concentration of direct thermal energy on the retina by the lens. It will occur only when the fireball is actually in the individual's field of vision and would be a relatively uncommon injury. Retinal burns may be sustained at considerable distances from the explosion. The height of burst and apparent size of the fireball, a function of yield and range will determine the degree and extent of retinal scarring. A scar in the central visual field would be more debilitating. Generally, a limited visual field defect, which will be barely noticeable, is all that is likely to occur.

When thermal radiation strikes an object, part will be reflected, part transmitted, and the rest absorbed. The fraction that is absorbed depends on the nature and color of the material. A thin material may transmit most of the radiation. A light-colored object may reflect much of the incident radiation and thus escape damage, like [[anti-flash white]] paint. The absorbed thermal radiation raises the temperature of the surface and results in scorching, charring, and burning of wood, paper, fabrics, etc. If the material is a poor thermal conductor, the heat is confined to the surface of the material.

The actual ignition of materials depends on how long the thermal pulse lasts and the thickness and moisture content of the target. Near ground zero where the energy flux exceeds 125 [[joule|J]]/cm<sup>2</sup>, what can burn, will. Farther away, only the most easily ignited materials will flame. Incendiary effects are compounded by secondary fires started by the blast wave effects such as from upset stoves and furnaces.[[File:Atomic_blast_Nevada_Yucca_1951_(better_quality).png|right|thumb|200px|The 19 kiloton [[nuclear testing|test shot]] Dog of [[Operation Tumbler-Snapper]] at the [[Nevada Proving Grounds]] on 1 May 1952. The red/orange color seen here in the cap of the [[mushroom cloud]] is largely due to the  [[nuclear fireball|fireball]]'s intense heat in combination with the [[oxygen]] and [[nitrogen]] gases ({{chem|O|2}} and {{chem|N|2}}) naturally found in air. These two atmospheric gases, though generally unreactive toward each other, form [[NOx]] species when heated to excess, specifically [[nitrogen dioxide]], which is largely responsible for the color. There was concern in the 1970s and 1980s, later proven unfounded, regarding [[Nuclear winter#Early work|fireball NOx and ozone loss]].]]
As thermal radiation travels more or less in a straight line from the fireball (unless scattered), any opaque object will produce a protective shadow that provides protection from the flash burn. Depending on the properties of the underlying surface material, the exposed area outside the protective shadow will be either burnt to a darker color, such as charring wood,<ref>{{cite web|url=http://www.pcf.city.hiroshima.jp/virtual/VirtualMuseum_e/visit_e/subcon/he113c.html|title=Damage by the Heat Rays/Shadow Imprinted on an Electric Pole|website=www.pcf.city.hiroshima.jp|access-date=30 March 2018|archive-date=12 September 2019|archive-url=https://web.archive.org/web/20190912204915/http://www.pcf.city.hiroshima.jp/virtual/VirtualMuseum_e/visit_e/subcon/he113c.html|url-status=dead}}</ref> or a brighter color, such as asphalt.<ref>"Various other effects of the radiated heat were noted, including the lightening of asphalt road surfaces in spots that had not been protected from the radiated heat by any object such as that of a person walking along the road. Various other surfaces were discolored in different ways by the radiated heat." From the [http://www.cddc.vt.edu/host/atomic/hiroshim/hiro_med.html#FLASH_BURN Flash Burn] {{Webarchive|url=https://web.archive.org/web/20140224094011/http://www.cddc.vt.edu/host/atomic/hiroshim/hiro_med.html#FLASH_BURN |date=24 February 2014 }} section of [http://www.cddc.vt.edu/host/atomic/hiroshim/hiro_med.html "The Atomic Bombings of Hiroshima and Nagasaki"] , a report by the Manhattan Engineering District, 29 June 1946,</ref> If such a weather phenomenon as fog or haze is present at the point of the nuclear explosion, it [[Mie scattering|scatters the flash]], with [[radiant energy]] then reaching burn-sensitive substances from all directions. Under these conditions, opaque objects are therefore less effective than they would otherwise be without scattering, as they demonstrate maximum shadowing effect in an environment of perfect visibility and therefore zero scatterings. Similar to a foggy or overcast day, although there are few if any, shadows produced by the sun on such a day, the solar energy that reaches the ground from the sun's [[infrared]] rays is nevertheless considerably diminished, due to it being absorbed by the water of the clouds and the energy also being scattered back into space. Analogously, so too is the intensity at a range of burning flash energy attenuated, in units of J/cm<sup>2</sup>, along with the slant/horizontal range of a nuclear explosion, during fog or haze conditions. So despite any object that casts a shadow being rendered ineffective as a shield from the flash by fog or haze, due to scattering, the fog fills the same protective role, but generally only at the ranges that survival in the open is just a matter of being protected from the explosion's flash energy.<ref>{{cite web|url=https://www.fourmilab.ch/etexts/www/effects/eonw_7.pdf#zoom=100|title=Glasstone & Dolan 1977 Thermal effects Chapter|website=fourmilab.ch|access-date=30 March 2018}}</ref>

The thermal pulse also is responsible for warming the atmospheric nitrogen close to the bomb and causing the creation of atmospheric [[NOx]] smog components. This, as part of the [[mushroom cloud]], is shot into the [[stratosphere]] where it is responsible for [[ozone depletion|dissociating]] [[ozone]] [[ozone layer|there]], in the same way combustion NOx compounds do. The amount created depends on the yield of the explosion and the blast's environment. Studies done on the total effect of nuclear blasts on the ozone layer have been at least tentatively exonerating after initial discouraging findings.<ref>{{cite journal|first=J.D.|last=Christie|date=20 May 1976|title=Atmospheric ozone depletion by nuclear weapons testing|journal=Journal of Geophysical Research|issue=15|volume=81|pages=2583–2594|doi=10.1029/JC081i015p02583|bibcode=1976JGR....81.2583C}} This link is to the abstract; the whole paper is behind a paywall.</ref>

=== Firestorm ===
In [[Hiroshima]] on 6 August 1945, a tremendous [[firestorm]] developed within 20 minutes after detonation and destroyed many more buildings and homes, built out of predominantly 'flimsy' wooden materials.<ref name="osti.gov" /> A firestorm has gale-force winds blowing in towards the center of the fire from all directions. It is not peculiar to nuclear explosions, having been observed frequently in large forest fires and following incendiary raids during World War II. Despite fires destroying a large area of [[Nagasaki]], no true firestorm occurred in the city even though a higher yielding weapon was used. Many factors explain this seeming contradiction, including a different time of bombing than Hiroshima, terrain, and crucially, a lower fuel loading/fuel density than that of Hiroshima.
{{blockquote| 
''Nagasaki probably did not furnish sufficient fuel for the development of a firestorm as compared to the many buildings on the flat terrain at Hiroshima.''<ref>[https://www.fourmilab.ch/etexts/www/effects/eonw_7.pdf Glasstone & Dolan (1977) Thermal effects Chapter] p. 304</ref>}}
Scientists have consistently highlighted a lack of accounting for large urban firestorms in civilian and military nuclear response planning.<ref name="v270">{{cite book |last=Eden |first=L. |url=https://books.google.com/books?id=yDk5hfkyISUC&pg=PR9 |title=Whole World on Fire: Organizations, Knowledge, and Nuclear Weapons Devastation |publisher=Cornell University Press |year=2004 |isbn=978-0-8014-3578-2 |series=Cornell paperbacks |page=9 |access-date=2025-04-22}}</ref><ref name="b841">{{cite journal |last=Cotton |first=William R. |year=1985 |title=Atmospheric Convection and Nuclear Winter: A new simulation of a large urban firestorm shows how smoke and soot might enter the stratosphere and alter the earth's climate |url=http://www.jstor.org/stable/27853239 |journal=American Scientist |publisher=Sigma Xi, The Scientific Research Society |volume=73 |issue=3 |pages=275–280 |issn=0003-0996 |jstor=27853239 |access-date=2025-04-22}}</ref> Other sources state that modern&nbsp;city design and construction makes large firestorms unlikely and adequate shelter can provide protection, using the example of the conventional [[Bombing of Hamburg in World War II|bombing of Hamburg]].<ref name="e442">{{cite journal |last1=LUCAS |first1=KENNETH A. |last2=ORIENT |first2=JANE M. |last3=ROBINSON |first3=ARTHUR |last4=MACCABEE |first4=HOWARD |last5=MORRIS |first5=PAUL |last6=LOONEY |first6=GERALD |last7=KLINGHOFFER |first7=MAX |year=1990 |title=Efficacy of Bomb Shelters: With Lessons From the Hamburg Firestorm |journal=Southern Medical Journal |publisher=Southern Medical Association |volume=83 |issue=7 |pages=812–820 |doi=10.1097/00007611-199007000-00022 |pmid=2196693 |issn=0038-4348}}</ref><ref name="hps.org">{{cite Q|Q63152882}}, p. 24.  Note:  No citation is provided to support the claim that "a firestorm in modern times is unlikely".</ref>{{Dead link|date=April 2025}}{{Clear}}