A nuclear detonation produces effects that are overwhelmingly more significant than those produced by a conventional explosive, even if the nuclear yield is relatively low. A nuclear detonation differs from a conventional explosion in several ways. A typical nuclear detonation:
produces energy which, weight for weight, is millions of times more powerful than that produced by a conventional explosion;
instantaneously produces a very large and very hot nuclear fireball;
instantaneously generates an electromagnetic pulse (EMP) that can destroy or disrupt electronic equipment;
transmits a large percentage of energy in the form of heat and light within a few seconds that can produce burns and ignite fires at great distances;
emits, within the first minute, highly penetrating prompt nuclear radiation that can be harmful to life and damaging to electronic equipment;
creates, if it occurs in the lower atmosphere, an air blast wave that can cause casualties and damage at significant distances;
creates, if it is a surface or near-surface burst, a shock wave that can destroy underground structures;
emits residual nuclear radiation over an extended period of time; and
- can provide extended interference with communications signals.
Figure F.1 is a photograph of the nuclear fireball and “mushroom” cloud produced by the 21 kiloton (kt) test device “Dog” on November 1, 1951; the device was detonated at the Nevada Test Site as part of Operation Buster-Jangle.
It is important to understand the effects of nuclear weapons for two reasons. First, the United States must have trained specialists who are knowledgeable and capable of advising senior leaders about the predictable results and the uncertainties associated with the employment of U.S. nuclear weapons. Second, given that adversary nations have nuclear weapons capabilities and terrorists are known to be seeking nuclear capability, the United States must have an understanding of how much and what types of damage might be inflicted on a populated area or military unit by an enemy use of one or more nuclear weapons.
Nuclear detonations can occur on, below, or above the Earth’s surface. Ground zero (GZ) is the point on the Earth’s surface closest to the detonation. The effects of a nuclear weapon detonation can destroy unprotected or unhardened structures and systems and can harm or kill exposed personnel at great distances from the point of detonation, thereby affecting the successful outcome of a military mission or producing a large number of casualties in a populated area. Figure F.2 depicts Hiroshima after being attacked with a nuclear weapon on August 6, 1945.
This appendix describes the effects of various nuclear detonations and the impacts of these effects on people, equipment, and structures. See Appendix G: Nuclear Survivability, for a discussion of the programs established to increase the overall survivability of U.S. nuclear deterrent forces and to harden other military systems and equipment against the effects of nuclear weapons.
The effects of a nuclear weapon for people or objects close to ground zero are devastating. The survival of humans and objects at various distance from ground zero will depend on several factors. One factor that is especially significant for survival is the nuclear weapon’s yield. If properly employed, any one nuclear weapon should defeat any one military target. However, a few nuclear weapons with relatively low-yields (such as the yields of any nation’s first generation of nuclear weapons) will not defeat a large military force (such as the allied force that operated in the first Gulf War). A single, low-yield nuclear weapon employed in a major metropolitan area will produce total devastation in an area large enough to produce tens of thousands of fatalities. It will not “wipe-out” the entire major metropolitan area. The survival of thousands of people who are seriously injured or exposed to a moderate level of nuclear radiation will depend on the response of various federal, state, and local government agencies.
The yield of the nuclear detonation significantly affects the distances of the damage zones; specifically, larger detonations can produce more casualties and damage. This concept is illustrated in Figures F.3, F.4, and F.5.
F.2 General Concepts and Terms
An explosion of any kind generates tremendous force through the release of a large amount of energy into a limited amount of space in a short period of time. This sudden release of energy increases the temperature and pressure of the immediate area to such a degree that all materials present are transformed into hot compressed gases. As these gases seek equilibrium, they expand rapidly outward in all directions, creating a shock wave or blast wave that has tremendous destructive potential. In a conventional explosion, almost all of the energy goes into producing the blast wave; only a small percentage of the energy produces a visible thermal radiation flash.
A typical nuclear detonation will produce blast, thermal, and nuclear radiation. The distribution of energy is primarily a function of weapon design, yield, and height of burst (HOB). A nuclear weapon’s output can be tailored to increase its ability to destroy specific types of targets, but a detonation of a typical fission-design weapon at or near the ground will result in approximately 50 percent of the energy producing air blast, ground shock, or both, 35 percent of the energy producing thermal radiation (intense light and heat), and 15 percent of the energy producing nuclear radiation. Figure F.6 depicts this energy distribution.
The yield of a nuclear detonation is normally expressed in terms of an equivalent amount of energy released by a conventional explosive. A one kiloton nuclear detonation releases the same amount of total energy as 1,000 tons (approximately 2.2 million pounds) of the conventional explosive trinitrotoluene (TNT), or approximately 1012 calories of energy. A one megaton (MT) nuclear detonation releases the same amount of energy as one million tons of TNT.
A typical nuclear weapon detonation will produce a huge number of X-rays, which heat the air around the detonation to extremely high temperatures, causing the heated air to expand and form a large fireball within a small fraction of a second. The size of the immediate fireball is a function of yield and the surrounding environment. Figure F.7 shows the size of the immediate fireball for selected yields and environments.
The immediate fireball reaches temperatures in the range of tens of millions of degrees, i.e., as hot as the interior temperatures of the sun. Inside the fireball, the temperature and pressure cause a complete disintegration of molecules and atoms. While current targeting procedures do not consider the fireball to be one of the primary effects of a weapon, a nuclear fireball could be used to defeat special types of target elements; for example, a nuclear fireball could incinerate chemical or biological agents.
In a typical nuclear detonation, because the fireball is so hot, it immediately begins to rise in altitude. As it rises, a vacuum effect is created under the fireball, and air that had been pushed away from the detonation rushes back toward the fireball, causing an upward flow of air and dust that follows it. This forms the stem of a mushroom-shaped cloud.
As the fireball rises, it will also be blown downwind. Most of the dust and other material that was in the stem of the mushroom-shaped cloud will drop back to the ground around ground zero. If there is a strong wind, some of this material may be blown downwind. After several minutes the cloud will reach an altitude at which its vertical movement slows, and after approximately ten minutes, it will reach its stabilized cloud height, usually tens of thousands of feet in altitude. After reaching its stabilized cloud height, the cloud will gradually laterally expand over a period of hours to days, thereby becoming much larger but also much less dense. Some of the material from the top of the cloud could be drawn to higher altitudes. After a period of weeks to months, the cloud will have dispersed to the extent that it covers a very large area; at this point, it will have very little radioactivity remaining.
Thermal radiation is electromagnetic radiation in the visible light spectrum that can be sensed as heat and light. A typical nuclear detonation will release thermal radiation in two pulses. During low-yield detonations, the two pulses occur too quickly to be noticeable without special sensor equipment. For very large yield detonations (one megaton or more) on clear days, the two pulses could be sensed by people at great distances from the detonation (a few tens of kilometers), and the second pulse would remain intense for ten seconds or longer. Thermal radiation is maximized with a low-air burst; the optimum height of burst to maximize the thermal effect increases with yield.
Thermal radiation can ignite wood frame buildings and other combustible materials at significant distances from the detonation. It can also cause burns to exposed skin directly or indirectly if clothing ignites or the individual is caught in a fire ignited by the radiation. Anything that casts a shadow or reduces light, including buildings, trees, dust from the blast wave, heavy rain, and dense fog, provides some protection against thermal burns or the ignition of objects. Transparent materials, such as glass or plastic, will slightly attenuate thermal radiation. Figure F.8 identifies the different types of burns and their approximate maximum distances at selected nuclear yields.
Flash blindness, or “dazzle,” is a temporary loss of vision caused when eyes are overwhelmed with intense thermal light. On a clear night, dazzle may last for up to thirty minutes and may affect people at distances of tens of kilometers. On a clear day, dazzle can affect people at distances beyond those for first degree burns; however, it lasts for a shorter period of time. Because thermal radiation can be scattered and reflected in the air, flash blindness can occur regardless of whether an individual is looking toward the detonation. At distances at which it can produce a first degree burn, thermal radiation is intense enough to penetrate through the back of the skull to overwhelm the eyes.
Retinal burns can occur at great distances for individuals looking directly at the fireball at the moment of the nuclear detonation. Further, if the yield is large enough and the duration of the second thermal pulse is longer than one second, some people might look toward the detonation and suffer retinal burns. Normally, retinal burns cause a permanent blindness to a small portion of the eye in the center of the normal field of vision.
A surface burst would reduce the incidence of both temporary blindness and retinal burns.
In order for thermal radiation to cause burns or ignition, the individual or object must be in direct line of sight from the detonation. Thermal radiation is thus maximized with a low-air burst (rather than a surface burst) because the higher height of detonation provides direct line of sight to much greater distances.
Because thermal radiation can start fires and cause burns at such great distances, if a nuclear weapon were employed against a populated area, on a clear day, with an air burst at approximately the optimum height of burst, it is likely that the thermal effects would account for more casualties than any other effect. With a surface burst or if rain or fog were in the area, the thermal radiation effects would be reduced.
The effects of thermal radiation can be reduced with protective enclosures, thermal protective coatings, and the use of non-flammable clothing, tools, and equipment. Thermal protective coatings include materials that swell when exposed to flame (thus absorbing the heat rather than allowing it to penetrate through the material) and ablative paints, which act like a melting heat shield. Materials like stainless steel, as opposed to temperature-sensitive metals like aluminum, are used to protect against thermal radiation. Similarly, higher-temperature resins are used in forming fiberglass structures. In order to reduce the amount of absorbed energy, light colors and reflective paints are also used. For effective thermal hardening, the use of combustible materials is minimized. Finally, to mitigate the effects of thermal radiation, it is important to protect items prone to melting—such as rubber gaskets, O-rings, and seals—from direct exposure.F.5 Air Blast
In the case of surface and low-air bursts, the fireball expands, pushing air or ground soil/rock/water immediately away from the point of the detonation. Above the ground, a dense wall of air traveling at great speed breaks away from the immediate fireball. Initially, this blast wave moves at several times the speed of sound, but it quickly slows to a point at which the leading edge of the blast wave is traveling at the speed of sound, and it continues at this speed as it moves farther away from ground zero. Shortly after breaking away from the fireball, the wall of air reaches its maximum density of overpressure (over the nominal air pressure). As the blast wave travels away from this point, the wall of air becomes wider and loses density, and the overpressure continues to decrease.
At significant distances from ground zero, overpressure can have a crushing effect on objects as they are engulfed by the blast wave. In addition to overpressure, the blast wave has an associated wind speed as it passes any object; this can be quantified as dynamic pressure that can move, rather than crush, objects. The blast wave has a positive phase and a negative phase for both overpressure and dynamic pressure.
As the blast wave hits a target object, the positive overpressure initially produces a crushing effect. If the overpressure is great enough, it can cause instant fatality. Less overpressure can collapse the lungs, and at lower levels, it can rupture the ear drums. Overpressure can implode a building. Immediately after the positive overpressure has begun to affect the object, dynamic pressure exerts a force that can move people or objects laterally very rapidly, causing injury or damage. Dynamic pressure can also strip a building from its foundation, blowing it to pieces.
As the positive phase of the blast wave passes an object, it is followed by a vacuum effect (i.e., the negative pressure caused by the lack of air in the space behind the blast wave). This is the beginning of the negative phase of dynamic pressure. The vacuum effect (negative overpressure) can cause a wood frame building to explode, especially if the positive phase has increased the air pressure inside the building by forcing air in through broken windows. The vacuum effect then causes the winds in the trailing portion of the blast wave to be pulled back into the vacuum. This produces a strong wind moving back toward ground zero. While the negative phase of the blast wave is not as strong as the positive phase, it may move objects back toward ground zero, especially if trees or buildings are severely weakened by the positive phase. Figure F.9 shows the overpressure in pounds per square inch (psi) and the approximate distances associated with various types of structural damage.
F.5.2 Air Blast Employment Factors
If the detonation occurs at ground level, the expanding fireball will push into the air in all directions, creating an ever-expanding hemispherical blast wave, called the incident wave. As the blast wave travels away, its density continues to decrease; after some significant distance, it loses its destructive potential and becomes a mere gust of wind. However, if the detonation is a low-air burst, a portion of the blast wave travels toward the ground and is then reflected off the ground. This reflected wave travels up and out in all directions, reinforcing the incident wave traveling along the ground. Because of this, air blast is maximized with a low-air burst rather than a surface burst.
If the terrain is composed of a surface that absorbs more thermal radiation than grass or soil, the thermal radiation will lead to a greater than normal heating of that surface. The surface will then give off heat before the arrival of the blast wave. This creates a “non-ideal” condition that causes the blast wave to become distorted when it reaches the heated surface, resulting in an abnormal reduction in the blast wave density and psi. Extremely cold weather (-50o Fahrenheit or colder) can lead to increased air blast damage distances. If a surface burst occurs in populated area or if there is rain and fog at the time of burst, the blast effect would probably account for more casualties than any other effect.
Structures and equipment can be reinforced to make them less vulnerable to air blast; however, any structure or piece of equipment will be destroyed if it is very close to the detonation. High priority facilities that must survive a close nuclear strike are usually constructed underground, making them much harder to defeat.
Individuals who sense a blinding white flash and intense heat coming from one direction should immediately fall to the ground and cover their heads with their arms. This provides the highest probability that the air blast will pass overhead without moving them laterally and that debris in the blast wave will not cause impact or puncture injuries. Exposed individuals who are very close to the detonation have no chance of survival. At distances at which a wood frame building can survive, however, exposed individuals significantly increase their chance of survival if they are on the ground when the blast wave arrives and if they remain on the ground until after the negative phase blast wave has moved back toward ground zero.
For surface or near-surface detonations, the fireball’s expansion and interaction with the ground causes a significant shock wave to move into the ground in all directions. This causes an underground fracture or “rupture” zone. The intensity and significance of the shock wave and the fracture zone decrease with distance from the detonation. A surface burst will produce significantly more ground shock than a near-surface burst in which the fireball barely touches the ground.
Underground structures, especially ones that are very deep underground, are not vulnerable to the direct primary effects of a low-air burst. The shock produced by a surface burst, however, may damage or destroy an underground target depending on the yield of the detonation, the soil or rock type, the depth of the target, and its structure. It is possible for a surface detonation to fail to crush a deep underground structure but to have an effective shock wave that crushes or buries entrance/exit routes and destroys connecting communications lines. This could cause the target to be “cut-off” and render it, at least temporarily, incapable of performing its intended function.
Normally, a surface burst or shallow sub-surface burst is used to attack deeply buried targets. As a rule of thumb, a one kiloton surface detonation can destroy an underground facility as deep as a few tens of meters. A one megaton surface detonation can destroy the same target as deep as a few hundreds of meters.
Deeply buried underground targets can be attacked through the employment of an earth-penetrating warhead to produce a shallow sub-surface burst. Only a few meters of penetration into the earth is required to achieve a “coupling” effect, in which most of the energy that would have gone up into the air with a surface burst is trapped by the material near the surface and reflected downward to reinforce the original shock wave. This reinforced shock wave is significantly stronger and can destroy deep underground targets to distances that are usually between two and five times deeper than those destroyed through the employment of a surface burst. Ground shock is the governing effect for damage estimation against any underground target.
Underground facilities and structures can be buried deeper to reduce their vulnerability to damage or collapse from a surface or shallow sub-surface detonation. Facilities and equipment can be built with structural reinforcement or other unique designs to decrease their vulnerability to ground shock. To ensure functional survivability, entrance and exit route requirements and communications lines connected to ground-level equipment must be considered.
In the case of near-surface, surface, and shallow sub-surface bursts, the fireball’s interaction with the ground causes it to engulf much of the soil and rock within its radius and remove that material as it moves upward. This removal of material results in the formation of a crater. A near-surface burst would produce a small, shallow crater. The crater from a surface burst with the same yield would be larger and deeper; crater size is maximized with a shallow sub-surface burst at the optimum depth. The size of the crater is a function of the yield of the detonation, the depth of burial, and the type of soil or rock.
For deeply buried detonations, such as those created with underground nuclear testing, the expanding fireball creates a spherical volume of hot radioactive gases. As the radioactive gas cools and contracts, the spherical volume of space becomes an empty cavity with a vacuum effect. The weight of the heavy earth above the cavity and the vacuum effect within the cavity cause a downward pressure for the earth to fall in on the cavity. This can occur unpredictably at any time from minutes to months after the detonation. When it occurs, the cylindrical mass of earth collapsing down into the cavity will form a crater on the surface, called a subsidence crater. Figure F.10 shows the Sedan Crater formed when a 104 kiloton explosive buried under 635 feet of desert alluvium was fired at the Nevada Test Site on July 6, 1962, displacing 12 million tons of earth. The crater is 320 feet deep and 1,280 feet in diameter.
If a crater has been produced by a recent detonation near the surface, it will probably be radioactive. Individuals required to enter or cross such a crater could be exposed to significant levels of ionizing radiation, possibly enough to cause casualties or fatalities.
If a deep underground detonation has not yet formed the subsidence crater, it would be very dangerous to enter the area on the surface directly above the detonation.
Normally, the wartime employment of nuclear weapons does not use crater formation to attack targets. At the height of the Cold War, however, North Atlantic Treaty Organization (NATO) forces had contingency plans to use craters from nuclear detonations to channel, contain, or block enemy ground forces. The size of the crater and its radioactivity for the first several days would produce an obstacle that would be extremely difficult, if not impossible, for a military unit to cross.
A crater by itself does not present a hazard to people or equipment, unless an individual tries to drive or climb into the crater. In the case of deep underground detonations, the rule is to keep away from the area where the subsidence crater will be formed until after the collapse occurs.
An underwater nuclear detonation generates a shock wave in a manner similar to that in which a blast wave is formed in the air. The expanding fireball pushes water away from the point of detonation, creating a rapidly moving dense wall of water. In the deep ocean, this underwater shock wave moves out in all directions, gradually losing its intensity. In shallow water, it can be distorted by surface and bottom reflections. Shallow bottom interactions may reinforce the shock effect, but surface interaction will generally mitigate the shock effect.
If the yield is large enough and the depth of detonation is shallow enough, the shock wave will rupture the water’s surface. This can produce a large surface wave that will move away in all directions. It may also produce a “spray dome” of radioactive water above the surface.
If a submarine is close enough to the detonation, the underwater shock wave will be strong enough to rapidly move the vessel. This near-instantaneous movement could force the ship against the surrounding water with a force beyond its design capability, causing a structural rupture of the vessel. The damage to the submarine is a function of weapon yield, depth of detonation, depth of the water under the detonation, bottom conditions, and the distance and orientation of the submarine. People inside the submarine are at risk if the boat’s structure fails. Even if the submarine structure remains intact, the lateral movement may cause injuries or fatalities to those inside the submarine.
Surface ships may be vulnerable to the underwater shock wave striking their hull. If the detonation produces a significant surface wave, it can damage surface ships at greater distances. If ships move into the radioactive spray dome, the dome could present a radioactive hazard to people on the ship.
Both surface ships and submarines can be designed to be less vulnerable to the effects of underwater nuclear detonations. However, any ship or submarine will be damaged or destroyed if it is close enough to a nuclear detonation.
Nuclear radiation is ionizing radiation emitted by nuclear activity. It consists of neutrons, alpha and beta particles, and electromagnetic energy in the form of gamma rays. Gamma rays are high-energy photons of electromagnetic radiation with frequencies higher than visible light or ultraviolet rays. Gamma rays and neutrons are produced from fission events. Alpha and beta particles and gamma rays are produced by the radioactive decay of fission fragments. Alpha and beta particles are absorbed by atoms and molecules in the air at short distances and are insignificant compared with other effects. Gamma rays and neutrons travel great distances through the air in a general direction away from ground zero.
Because neutrons are produced almost exclusively by fission events, they are produced in a fraction of a second, and there are no significant number of neutrons produced after that. Conversely, gamma rays are produced by the decay of radioactive materials; they will be produced for years after the detonation. Most of these radioactive materials are initially in the fireball. For surface and low-air bursts, the fireball will rise quickly, and within approximately one minute, it will be at an altitude high enough that none of the gamma radiation produced inside the fireball will have any impact to people or equipment on the ground. For this reason, initial nuclear radiation is defined as the nuclear radiation produced within one minute post-detonation. Initial nuclear radiation is also called prompt nuclear radiation.
The huge number of gamma rays and neutrons produced by a surface, near-surface, or low-air burst may cause casualties or fatalities to people at significant distances. For a description of the biological damage mechanisms, see the section on the biological effects of ionizing radiation. The unit of measurement for radiation exposure is the centi-Gray (cGy). Figure F.11 shows selected levels of exposure, the associated near-term effects on humans, and the distances by yield. The 450 cGy exposure dose level is considered to be the lethal dose for 50 percent of the population (LD50), with medical assistance. People who survive at this dose level would have a significantly increased risk of contracting mid-term and long-term cancers.
Low levels of exposure can increase an individual’s risk for contracting long-term cancers. For example, in healthy male adults ages 20 to 40, an exposure of 100 cGy will increase the risk of contracting any long-term cancer by approximately ten to fifteen percent and lethal cancer by approximately six to eight percent.
Initial nuclear radiation can also damage the electrical components in certain equipment. See the section on transient radiation effects on electronics (TREE) below.
The ground absorbs more gamma rays and neutrons than the air. Almost half of the initial nuclear radiation resulting from a surface burst will be quickly absorbed by the earth. In the aftermath of a low-air burst, half of the nuclear radiation will travel in a downward direction, but much of that radiation will be scattered and reflected by atoms in the air. This will add to the amount of radiation traveling away from ground zero. Because of this, initial nuclear radiation is maximized with a low-air burst.
Initial nuclear radiation effects can be predicted with reasonable accuracy. Some non-strategic or terrorist targets may include people as a primary target element. In this case, initial nuclear radiation is considered with air blast to determine the governing effect. Initial nuclear radiation is always considered for safety (if safety of populated areas or friendly troop personnel is a factor), and safety distances are calculated based on a “worst-case” assumption, i.e., that there will be maximum initial radiation effect and that objects in the target area will not shield or attenuate the radiation.
Individuals can do very little to protect themselves against initial nuclear radiation after a detonation has occurred because initial radiation is emitted and absorbed in less than one minute. The Department of Defense has developed an oral chemical prophylactic to reduce the effects of ionizing radiation exposure, but the drug does not reduce the hazard to zero. Just as with most of the other effects, if an individual is very close to the detonation, it will be fatal.
Generally, structures are not vulnerable to initial nuclear radiation. Equipment can be hardened to make electronic components less vulnerable to initial nuclear radiation.
Residual nuclear radiation consists of alpha and beta particles and gamma rays emitted from nuclei during radioactive material decay. There are two primary categories of residual nuclear radiation that result from a typical detonation: induced radiation and fallout. These categories of residual radiation also result from a deep underground detonation, but the radiation remains underground unless radioactive gases vent from the fireball or residual radiation escapes by another means, for example, through an underground water flow. An exo-atmospheric detonation creates a cloud in orbit that could remain significantly radioactive for many months.
For typical surface or low-air burst detonations, there are two types of induced radiation. The first type is neutron-induced soil on the ground, called an “induced pattern.” Neutrons emitted from the detonation are captured by light metals in the soil or rock near the ground surface. These atoms become radioactive isotopes capable of emitting, among other things, gamma radiation. The induced radiation is generally created in a circular pattern around the ground zero. It is most intense at ground zero immediately after the detonation. The intensity decreases over time and with distance from ground zero. In normal soil, it takes approximately five to seven days for induced radiation to decay to a safe level.
The second type of induced radiation is the production of carbon-14 by the absorption of fission neutrons in nitrogen in the air. Carbon-14 atoms can remain suspended in the air, are beta particle emitters, and have a long half-life (5,715 years).
Fallout is the release of small radioactive particles that drop from the fireball to the ground. In most technical jargon, fallout is defined as the fission fragments from the nuclear detonation. However, the fireball will contain other types of radioactive particles that will also fall to the ground and contribute to the total radioactive hazard. These include the radioactive fissile material that did not undergo fission (no weapon fissions 100 percent of the fissile material) and material from warhead components that have been induced with neutrons and become radioactive.
Residual gamma radiation is colorless, odorless, and tasteless. Unless there is an extremely high level of radiation, it cannot be detected with the five senses.
Usually a deep underground detonation presents no residual radiation hazard to people or objects on the surface. If there is an accidental venting or some other unintended escape of radioactivity, however, it could become a radioactive hazard to people in the affected area. The residual nuclear cloud from an exo-atmospheric detonation could damage electronic components in some satellites over a period of time (usually months or years) depending on how close a satellite gets to the radioactive cloud, the frequency of the satellite passing near the cloud, and its exposure time.
If a nuclear device is detonated in a populated area, it is possible that the induced radiation could extend to distances beyond building collapse. This is especially true with the employment of a low-yield device such as would likely be the case with a terrorist nuclear device. This could cause first responders who are not trained to understand induced radiation to accidentally move into an area that is still radioactively hot. Without radiation detectors, the first responders would not be aware of the radioactive hazard.
Between the early-1950s and 1962, when the four nuclear nations were conducting above ground nuclear testing, there was a two to three percent increase in total carbon-14 levels worldwide. Gradually, the amount of carbon-14 is returning to pre-testing levels. While there are no known casualties attributed to the increase, it is logical that any increase in carbon-14 levels over the natural background level could be an additional risk.
Normally, fallout should not be a hazardous problem for a detonation that is a true air burst. However, if rain or snow is falling in the target area, radioactive particles could be “washed-out” of the fireball, creating a hazardous area of early fallout. If a detonation is a surface or near-surface burst, early fallout would be a significant radiation hazard around ground zero and downwind.
If the detonation is a true air burst in which the fireball does not interact with the ground or any significant structure, the size and heat of the fireball will cause it to retain almost all of the weapon debris (usually one or at most a few tons of material) as it moves upward in altitude and downwind. In this case, very few particles fall to the ground at any moment, and there is no significant radioactive hot-spot on the ground caused by the fallout. The fireball will rise to become a long-term radioactive cloud. The cloud will travel with the upper atmospheric winds, and it will circle the hemisphere several times over a period of months before it dissipates completely. Most of the radioactive particles will decay to stable isotopes before falling to the ground. The particles that reach the ground will be distributed around the hemisphere at the latitudes of the cloud travel route. Even though there would be no location receiving a hazardous amount of fallout radiation, certain locations on the other side of the hemisphere could receive more fallout (measurable with radiation detectors) than the area near the detonation. This phenomenon is called worldwide fallout.
If the fireball interacts with the ground or any significant structure (for example, a large bridge or a building), the fireball would have different properties. In addition to the three types of radioactive material mentioned above, the fireball would also include radioactive material from the ground (or from the structure) that was induced with neutrons. The amount of material in the fireball would be much greater than the amount with an air burst. For a true surface burst, a one kiloton detonation would extract thousands of tons of earth up into the fireball (although only a small portion would be radioactive). This material would disintegrate and mix with the radioactive particles. As large and hot as the fireball is (for a one kiloton detonation, almost 200 feet in diameter and tens of millions of degrees), it has no potential to carry thousands of tons of material. Thus, as the fireball rises, it would begin to release a significant amount of radioactive dust, which would fall to the ground and produce a radioactive fallout pattern around ground zero and in areas downwind. The intensity of radioactivity in this fallout area would be hazardous for weeks. This is called early fallout, and it is caused primarily by a surface burst detonation regardless of the weapon design. Early fallout would be a concern in the case of the employment of a nuclear threat device during a terrorist attack.
There are four actions that provide protection against residual radiation. First, personnel with a response mission should enter the area with at least one radiation detector, and all personnel should employ personal protective equipment (PPE). While the PPE will not stop the penetration of gamma rays, it will prevent the responder personnel from breathing in any airborne radioactive particles. Second, personnel should only be exposed to radioactivity for the minimum time possible to accomplish a given task. Third, personnel should remain at a safe distance from radioactive areas. Finally, personnel should use shielding when possible to further reduce the amount of radiation received. It is essential for first-responder personnel to follow the principles of PPE: time, distance, and shielding.
Equipment may be designed to be “rad-hard” if required. See Appendix G: Nuclear Survivability, for a discussion of the U.S. nuclear survivability program.
Ionizing radiation is any particle or photon that can produce an ionizing event, i.e., strip one or more electrons away from their parent atom. It includes alpha particles, beta particles, gamma rays, cosmic rays (all produced by nuclear actions), and X-rays (not produced by nuclear actions).
Ionizing events cause biological damage to humans and other mammals. Figure F.12 lists the types of biological damage associated with select ionizing events. Generally, the greater the exposure dose, the greater the biological problems caused by the ionizing radiation.
At medium and high levels of exposure, there are near-term consequences, including impaired performance, that lead to casualties and death. See Figure F.11 for a description of these problems at selected dose levels. Individuals who survive at these dose levels have a significantly higher probability of contracting mid-term and long-term cancers.
At low levels of exposure, ionizing radiation does not cause any near-term medical problems. However, at the 75 cGy level, approximately five percent of healthy adults would experience mild threshold symptoms, i.e., transient mild headaches and mild nausea. At the 100 cGy level, approximately ten to fifteen percent of healthy adults would experience threshold symptoms, and a smaller percentage would experience some vomiting. Low levels of ionizing radiation exposure also result in a higher probability of contracting mid-term and long-term cancers. Figure F.13 shows healthy adults’ increased risk of contracting cancer after ionizing radiation exposure, by gender.
F.11.2 Ionizing Radiation Protection
Protection from ionizing radiation can be achieved through shielding. Most materials will shield from radiation; however, some materials need to be present in significant amounts to reduce the penetrating radiation by half. Figure F.14 illustrates the widths required for selected types of material to stop half the gamma radiation (called “half-thickness”) and to stop 90 percent of the radiation (called “tenth-value thickness”).F.12 Electromagnetic Pulse
Electromagnetic pulse (EMP) is a very short duration pulse of low-frequency (long-wavelength) electromagnetic radiation (EMR). EMP is produced when a nuclear detonation occurs in a non-symmetrical environment, especially at or near the Earth’s surface or at high altitudes. The interaction of gamma rays, X-rays, and neutrons with the atoms and molecules in the air generates an instantaneous flow of electrons, generally in a direction away from the detonation. These electrons immediately change direction (primarily because of the Earth’s magnetic field) and velocity, emitting low frequency EMR photons. This entire process occurs almost instantaneously and produces a huge number of photons.
Any unprotected equipment with electronic components could be vulnerable to EMP. A large number of low-frequency photons can be absorbed by any antenna or any component that acts as an antenna. This energy moves within the equipment to unprotected electrical wires or electronic components and generates a flow of electrons. The electron flow becomes voltage within the electronic component or system. Modern electronic equipment using low voltage components can be overloaded with a voltage beyond its designed capacity. At low levels of EMP, this can cause a processing disruption or a loss of data. At increased EMP levels, certain electronic components will be destroyed. EMP can damage unprotected electronic equipment, including computers, vehicles, aircraft, communications equipment, and radars. EMP will not result in structural damage to buildings, bridges, etc.
EMP is not a direct hazard to humans. It is possible, however, that the indirect effects of electronics failing instantaneously in items such as vehicles, aircraft, and life-sustaining equipment in hospitals could cause injuries or fatalities.
A high-altitude detonation, or an exo-atmospheric detonation within a certain altitude range, will generate an EMP that could cover a very large region of the Earth’s surface, as large as 1,000 kilometers across. A surface or low-air burst would produce local EMP with severe intensity, traveling through the air out to distances of hundreds of meters. Generally, the lower the yield, the more significant is the EMP compared with air blast. Unprotected electronic components would be vulnerable. Electrical lines and telephone wires would carry the pulse to much greater distances, possibly 10 kilometers, and could destroy any electronic device connected to the power lines.
Because electronic equipment can be hardened against the effects of EMP, it is not considered in traditional approaches for damage estimation.
Electronic equipment can be EMP-hardened. The primary objective of EMP hardening is to reduce the electrical pulse entering a system or piece of equipment to a level that will not cause component burnout or operational upset. It is always cheaper and more effective to design EMP protection into the system during design development. Potential hardening techniques include the use of certain materials as radio frequency shielding filters, internal enclosed protective “cages” around essential electronic components, and enhanced electrical grounding and shielded cables. Additionally, equipment can be hardened if it is kept in closed protective cases or in EMP-protected rooms or facilities. Normally, the hardening that permits equipment to operate in intense radar fields (e.g., helicopters that operate in front of a ship’s radars) also provides a significant degree of EMP protection.
Because the EMP is of such short duration, home circuit-breakers, typical surge-protectors, and power strips are useless against EMP. These devices are designed to protect equipment from electrical surges caused by lightning, but EMP is thousands of times faster than the pulse of lightning.
Transient radiation effects on electronics refers to the damage to electronic components exposed to initial nuclear radiation gamma rays and neutrons.
The gamma rays and neutrons produced by a nuclear detonation are transient initial nuclear radiation that can affect electronic components and associated circuitry by penetrating deep into materials and electronic devices. Gamma rays can induce stray currents of electrons that generate harmful electromagnetic fields similar to EMP. Neutrons can collide with atoms in key electronic materials causing damage to the crystal (chemical) structure and changing electrical properties. While all electronics are susceptible to the effects of TREE, smaller, solid-state electronics such as transistors and integrated circuits are most vulnerable to these effects.
Although initial nuclear radiation may pass through material and equipment in a matter of seconds, the damage is usually permanent.
In the case of a high-altitude or exo-atmospheric burst, prompt gamma rays and neutrons can reach satellites or other space systems. If these systems receive large doses of this initial nuclear radiation, their electrical components can be damaged or destroyed. If a nuclear detonation is a low-yield surface or low-air burst, the prompt gamma rays and neutrons could be intense enough to damage or destroy electronic components at distances beyond those affected by air blast. Because electronic equipment can be hardened against the effects of TREE, it is not considered in traditional approaches to damage estimation.
Equipment that is designed to be protected against TREE is called “rad-hardened.” The objective of TREE hardening is to reduce the effect of the gamma and neutron radiation from damaging electronic components. Generally, special shielding designs can be effective, but TREE protection may include using shielded containers with a mix of heavy shielding for gamma rays and certain light materials to absorb neutrons. Just as with EMP hardening, it is always cheaper and more effective to design the EMP protection into the system during design development.F.14 Blackout
Blackout is the interference with radio and radar waves resulting from an ionized region of the atmosphere. Nuclear detonations, other than those underground or far away in outer space, generate the flow of a huge number of gamma rays and X-rays that move in a general direction away from the detonation. These photons produce a large number of ionizing events in the atoms and molecules in the air, creating a very large region of ions. A large number of electrons are stripped away from their atoms, and move in a direction away from the detonation. This leaves a large number of positively charged atoms closer to the detonation, creating an ionized region with positively charged atoms close to the detonation and negatively charged particles farther from the detonation.
Blackout cannot cause damage or injuries directly. The interference with communications or radar operations could cause accidents indirectly, for example, the loss of air traffic control—due to either loss of radar capability or the loss of communications—could affect several aircraft simultaneously.
A high-altitude or exo-atmospheric detonation would produce a very large ionized region of the upper atmosphere that could be as large as thousands of kilometers in diameter. This ionized region could interfere with communications signals to and from satellites and with AM radio transmissions relying on atmospheric reflection if those signals travel through or near the ionized region. Under normal circumstances, this ionized region interference would continue for a period of time up to several hours after the detonation. The ionized region can affect different frequencies out to different distances and for different periods of time.
A surface or low-air burst would produce a smaller ionized region of the lower atmosphere that could be as large as tens of kilometers in diameter. This ionized region could interfere with Very High Frequency (VHF) and Ultra High Frequency (UHF) communications signals and radar waves that rely on pin-point line-of-sight transmissions if those signals travel through or near the ionized region. Under normal circumstances, this low altitude ionized region interference would continue for a period of time up to a few tens of minutes after the detonation. Again, the ionized region can affect different frequencies out to different distances and for different periods of time.
There is no direct protection against the blackout effect.F.15 Nuclear Weapons Targeting Process
Nuclear weapons targeting is a direct function of nuclear weapons effects. Nuclear weapons targeting accounts for the capability of U.S. nuclear weapons, the predictable effects of those weapons, and the damage expectancy that results. It is a process by which damage requirements to adversary targets are calculated to determine which weapons to use to defeat them. The nuclear weapons targeting process is cyclical. It begins with guidance and priorities issued by the president, the secretary of defense, and the chairman of the Joint Chiefs of Staff (CJCS) in conjunction with appropriate allied command guidance and priorities. These objectives direct joint force and component commanders and the targeting process continues through the combat assessment phase. Figure F.15 illustrates the nuclear targeting cycle and is followed by a brief description of each phase.
Objectives and Guidance: Guidance and objectives are issued by the president and the CJCS while joint force and component commanders initiate the targeting cycle.
Target Development: Development of a target focuses on identifying and nominating critical elements of enemy military forces and their means of support for attack.
Weaponeering Assessment: Planners analyze each target nominated for a nuclear strike to determine the optimal means of nuclear attack. During this process, planners consider the employment characteristics of available weapons, including yields, delivery accuracy, and fuzing. Damage prediction, consequences of execution, and collateral damage preclusion are additional factors considered in this analysis. Target analysts use target information including location, size, shape, target hardness, and damage criteria (moderate or severe) as inputs to nuclear targeting methodologies.
Force Application: This phase integrates information concerning the target, the weapon system, and munitions types in addition to non-lethal force options to select specific weapons to attack specific targets.
Execution Planning and Force Execution: This phase involves final tasking order preparation and transmission; specific mission planning and material preparation at the unit level; and presidential authorization for use.
Combat Assessment: The final phase is a joint effort designed to determine if the required target effects are consistent with the military campaign objectives. Nuclear combat assessment is composed of two segments, battle damage assessment and a re-attack recommendation.
Damage criteria are standards identifying specific levels of destruction or material damage required for a particular target category. These criteria vary by the intensity of the damage and by the particular target category, class, or type.
Damage criteria are based on the nature of the target including its size, hardness, and mobility as well as the target’s proximity to military or non-military assets. These criteria provide a means by which to determine how best to strike particular targets and, following the attack, they provide a means by which to evaluate whether the target or target sets were sufficiently damaged to meet operational objectives.
Radius of damage (RD) is that distance from the nuclear weapon burst at which the target elements have a fifty percent probability of receiving at least the specified (severe/moderate) degree of damage. In strategic targeting, this has been called the weapon radius. Because some target elements inside the RD will escape the specified degree of damage while some outside the RD will be damaged, response variability results. The RD depends on the type of target, the yield of the weapon, the damage criteria, and the height of burst of the nuclear weapon.
Circular error probable (CEP) is an indicator of the delivery accuracy of a weapon system and is used as a factor in determining probable damage to a target. CEP is the radius within which fifty percent of the weapons aimed at one point are expected to land. A weapon is expected to land within one CEP of an aimpoint for desired ground zero (DGZ) fifty percent of the time.
Probability of damage (PD) is the probability of achieving at least the specified level of damage assuming the weapon arrives and detonates on target. It is expressed as fractional coverage for an area target and probability of damage for a point target. The PD is a function of nuclear weapons effects and weapons system delivery data including: yield, RD, CEP, and HOB.
Probability of arrival (PA) is the probability that the weapon will arrive and detonate in the target area as planned. The PA is calculated as a product of weapon system reliability (WSR), pre-launch survivability (PLS), and probability to penetrate (PTP).
PA = (WSR) x (PLS) x (PTP)
- WSR is the compounded reliability based on test data provided by the National Nuclear Security Administration (NNSA) for the warhead and the Military Services for the delivery system.
- PLS is the probability that the selected weapon system will survive a first strike by the enemy.
- PTP is the probability that the weapon system will survive enemy air defense measures and reach the target.
Damage expectancy (DE) is calculated as the product of the PD and the PA. DE accounts for both weapons effects and the probability of arrival in determining the probability of achieving at least the specified level of damage.
DE = (PA) x (PD)
Nuclear collateral damage is undesired damage or casualties produced by the effects of nuclear weapons. Such damage includes danger to friendly forces, civilians, and non-military-related facilities as well as the creation of obstacles and residual nuclear radiation contamination. Since the avoidance of casualties among friendly forces and non-combatants is a prime consideration when planning either strategic or theater nuclear operations, preclusion analyses must be performed to identify and limit the proximity of a nuclear strike to civilians and friendly forces. Following are specific techniques for reducing collateral damage.
- Reducing weapon yield: The size of the weapon needed to achieve the desired damage is weighed against the associated danger to areas surrounding the target.
- Improving accuracy: Accurate delivery systems are more likely to strike the desired aimpoint, thereby reducing both the required yield and the potential collateral damage.
- Employing multiple weapons: Collateral damage can be reduced by dividing one large target into two or more smaller targets and by using more than one lower-yield weapon rather than one high-yield weapon.
- Adjusting the height of burst: HOB adjustments, including the use of higher heights of burst to preclude any significant fallout, are a principal means of controlling or minimizing collateral damage.
- Offsetting the desired ground zero: Moving the DGZ away from target center may still achieve the desired weapon effects while avoiding or minimizing collateral damage.
Counter-value targeting directs the destruction or neutralization of selected enemy military and military-related targets such as industries, resources, and or/institutions that contribute to the ability of the enemy to wage war. In general, weapons required to implement this strategy need not be as numerous nor as accurate as those required to implement a counter-force targeting strategy because counter-value targets tend to be softer and less protected than counter-force targets.
Counter-force targeting is a strategy that employs forces to destroy the military capabilities of an enemy force or render them impotent. Typical counter-force targets include: bomber bases, ballistic missile submarine bases, intercontinental ballistic missile (ICBM) silos, antiballistic and air defense installations, command and control centers, and weapons of mass destruction storage facilities. Generally, the nuclear forces required to implement a counter-force targeting strategy are larger and more accurate than those required to implement a counter-value strategy. Counter-force targets generally tend to be harder, more protected, more difficult to find, and more mobile than counter-value targets.
Layering is a targeting methodology that employs more than one weapon against a target. This method is used to either increase the probability of target destruction or improve the probability that a weapon will arrive and detonate on target to achieve a specific level of damage.
Cross-targeting incorporates the concept of “layering,” and also uses different delivery platforms for employment against one target to increase the probability of at least one weapon arriving at that target. Using different delivery platforms such as ICBMs, submarine-launched ballistic missiles, or aircraft-delivered weapons increases the probability of achieving the desired damage or target coverage.
 For the purposes of this appendix, a “typical” nuclear detonation is one that occurs on the Earth’s surface, or at a height of burst low enough for the primary effects to cause damage to surface targets. Detonations that are exo-atmospheric, high altitude, or deeply buried underground have different effects.
 A near-surface burst is a detonation in the air that is low enough for the immediate fireball to touch the ground.
 Residual nuclear radiation may be harmful to humans if the detonation is close to the ground; if the detonation is exo-atmospheric, residual radiation may damage electronic components in satellites.
 This appendix is written to be technically correct but also to be comprehensible through the use of terms and descriptions that can be understood by people without an academic education in the sciences. A greater level of technical detail can be found in the more definitive documents on the subject such as the Defense Nuclear Agency Effects Manual Number 1 (DNA EM-1) published by the forerunner organization to the current Defense Threat Reduction Agency (DTRA), or The Effects of Nuclear Weapons, 1977, by Samuel Glasstone and Philip Dolan.
 Proper employment includes using the required yield at the required location with an effective height of burst (e.g., a high-altitude detonation will not destroy a building or a bridge). Examples of single military targets include: one or a group of structures in a relatively small area; special contents (e.g., biological agents) within a structure; a missile silo or launcher position; a military unit (e.g., a single military ship, an air squadron, or even a ground-force battalion); a command post; or a communications site.
 A large-yield detonation would have a hotter fireball, and it would rise to a higher altitude than a low-yield detonation. A fireball from a one megaton detonation would rise to an altitude of between 60,000 and 70,000 feet.
 The distances in Figure F.8 are based on scenarios in which the weather is clear, there are no obstacles to attenuate thermal radiation, and the weapon is detonated as a low-air burst at the optimum HOB to maximize the thermal effect.
 For a one kiloton, low-air burst nuclear detonation, the immediate fireball would be approximately 30 meters (almost 100 feet) in radius and approximately 60 meters (almost 200 feet) in diameter.
 At a short distance beyond the radius of the immediate fireball, the blast wave would reach a density of thousands of pounds per square inch.
 The distances in Figure F.9 are based on an optimum height of burst to maximize the blast effect, and the existence of no significant terrain that would stop the blast wave (e.g., the side of a mountain). For surface bursts, the distances shown are reduced by approximately 30 to 35 percent for the higher overpressures, and by 40 to 50 percent for one psi.
 The amount of increased depth of damage is primarily a function of the yield and the soil or rock type.
 For a one kiloton detonation, the maximum crater size would have a burial depth between 32 and 52 meters, depending on the type of soil or rock.
 Ionizing radiation is defined as electromagnetic radiation (gamma rays or X-rays) or particulate radiation (alpha particles, beta particles, neutrons, etc.) capable of producing ions (electrically charged particles) directly or indirectly in its passage through, or interaction with, matter.
 A photon is a unit of electromagnetic radiation consisting of pure energy and zero mass; the spectrum of photons include AM radio waves, FM radio waves, radar- and micro-waves, infrared waves, visible light, ultraviolet waves, X-rays, and gamma/cosmic rays.
 Both gamma rays and neutrons will be scattered and reflected by atoms in the air, causing each gamma photon and each neutron to travel a “zig-zag” path moving generally away from the detonation. Some neutrons and photons may be reflected so many times that, at a significant distance from the ground zero, they will be traveling back toward the ground zero.
 One cGy is an absorbed dose of radiation equivalent to 100 ergs of ionizing energy per gram of absorbing material or tissue. The term centi-Gray replaced the older term radiation absorbed dose (RAD).
 For the purposes of this appendix, all radiation doses are assumed to be acute (total radiation received within approximately 24 hours) and whole-body exposure. Exposures over a longer period of time (chronic), or exposures to an extremity (rather than to the whole body) could have less effect on a person’s health.
 Calculated from data in Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII - Phase 2, National Academy of Sciences, Committee to Assess Health Risks from Exposure to Low Levels of Ionizing Radiation, 2006.
 Neutrons induced into typical soil are captured primarily by sodium, manganese, silicon, and aluminum atoms.
 PPE for first-responders includes a sealed suit and self-contained breathing equipment with a supply of oxygen.
 EMP can also be produced by using conventional methods.