The Multiverse

Ordnance Netbook - Nuclear Weapons

"The splitting of the atom has changed everything save our mode of thinking and thus we drift toward unparalleled catastrophe"
- Albert Einstein

A Nuclear Explosion

When a nuclear weapon explodes, in about a millionth of a second a temperature of up to eighteen million degrees Fahrenheit, comparable to that inside the sun, is produced. About half of this is immediately lost in the close vicinity of the explosion as a luminous white fireball appears, expands and begins to rise.

For up to a minute, energy in the forms of radiation, EMP (electromagnetic pulse), light, heat, sound, and blast is released in all directions. The fireball then ceases to be luminous and begins to cool as its cloud rises many thousands of meters at up to 480 kilometers per hour. As the cloud billows out into its eventual mushroom shape it sucks up after it a column of dust from the earth's surface. This dust mixes with residue of the weapon and becomes radioactive fallout.

Components of the Nuclear Explosion

Light
This is largely ultraviolet and infrared, more intense than it appears to be, and liable to cause blindness, even though sight may return within a few days.

Heat
One third of the energy of a nuclear weapon is emitted in this form. It radiates in straight lines at the velocity of light, but has little penetrating power and is weakened by haze or mist. Its range, however, is greater than that of blast or of initial radiation, and it may cause injury or death to those exposed and damage to property by starting fires.

Blast
A wave of compressed air moves away from the site of a nuclear explosion at about the speed of sound. Lasting several seconds, it maintains pressure upon objects in its path in a manner more usually associated with a very high wind than the shock wave of an explosion. It is the main cause of damage to buildings, and a hazard to those outside or within. A wave of air rushes back in to fill the void seconds after the initial blast wave passes. This wave is not as strong, maybe several hundred kilometers per hour.

Side Affects of the Nuclear Explosion

Radiation

The electromagnetic spectrum consists of cosmic rays, gamma rays, x-rays, ultraviolet rays, visible light rays, infrared rays, and radio rays. Of these, gamma rays are of chief concern to us. Gamma rays, alpha and beta particles, and neutrons result from decay of radioactive substances, and all four are emitted following a nuclear explosion. Their effects are all referred to below as radiation.

When ionizing radiation enters the body, some of it is absorbed. This ionizes molecules in some of the body's cells, producing chemical changes so they cease to function. What is called "radiation sickness" may then occur.

Fallout

With surface explosions, or at altitudes low enough for the fireball to touch the ground, huge quantities of earth and debris, together with the fission products, are sucked into the fireball. As the fireball cools, the radioactivity condenses on the particles that were lifted from the ground; many of these are large particles and they come down by the force of gravity within a day, or, at distances not too far from the burst, some hundreds of kilometers. This constitutes the "local" or "early" fallout. The extent and location of the early fallout depends primarily on the meteorological conditions, e.g. the velocity and direction of the wind. They also depend on precipitation conditions; the particles may come down to earth with the rain or snow, which is referred to as "rainout" or "snowout".

In addition to surface bursts and air bursts, underwater bursts occur at times. Radioactive fission products would mainly be absorbed by the water. However, some would escape to produce radioactive materials carried in a cloud of fog/spray which could drift in over land, adding to the exposure.

It should be noted that all nuclear weapons detonated in the air give rise to fallout, but where and when it occurs depends primarily on the altitude of the explosion. With explosions in the air at altitudes such that the fireball does not touch the ground, the fission products, which are initially in gaseous form, rise with the fireball to great heights into the troposphere or stratosphere. When the temperature of the fireball becomes sufficiently low, the radioactive materials form particles, through condensation and coagulation. These particles are very small, and as a result their descent is very slow; it may take many months before they come down to the ground.

EMP (Electro-magnetic Pulse)

This is a byproduct of the immediate energy release from a detonated nuclear device which, as well as the other effects mentioned above, also has the effect of altering the electrical properties of electrons in the nearby atmosphere. This can produce intense electrical and magnetic fields that can extend for considerable distances from the point of detonation. The resultant electrical current eddies which pass through these disturbed electrical fields give rise to the EMPs that can, by themselves, produce so much energy that they can severely affect electronic-based equipment and electrical and radar transmissions to the point of destroying equipment circuits, components and communications. The effects of EMP diminish sharply with distance from the point of detonation but can still cause damage at ranges greater than those for the other 3 major effects (under certain circumstances). Their main significance will be to communications; the communications networks will probably be rendered inoperative for considerable periods of time by interference from EMPs, and the results of such breakdowns can well be imagined. At the very moment when radio and other links (including land lines) between various command levels are at their most important the EMPs will render them virtually useless over large areas. Even when a nuclear explosion has passed, the reverberations produced by the EMP in the atmosphere may well linger to cause continued interruptions. Heavy concentrations of fallout will produce radiation to create further interference across radio and other communication frequencies.

Mass Fires

There are two types of mass fires - the conflagration and the firestorm. Both are created from the hundreds of individual fires that are started as a result of the nuclear blast.

Conflagration Fire

The conflagration is a large-area fire which is moved by a strong wind, devouring everything in its path. The wind causes a literal wall of flame to form and to move before it. This type of mass fire can be expected to occur in many forests and in dry grassy areas. If you consider the damage done over the last few years by brush and forest fires in California, you can begin to understand the destruction that would be caused by hundreds of such fires massing together.

Firestorm

The firestorm is a mass fire that burns intensely in one area. As the many smaller fires burn, they cause air to be pulled into the area, and smoke and superhot gases then escape upward. Once this airflow pattern begins, it feeds on itself, creating a sort of a chimney effect. Once the phenomenon is fully developed the air flows into the area at between 80 and 115 kilometers per hour. Temperatures reach as high as 1000 to 2000 degrees Fahrenheit, so even things that aren't actually touched by flames are consumed and destroyed. Unlike the conflagration, a firestorm doesn't travel; it moves little, if at all, due the strong winds blowing in from all sides.

A firestorm can form in an area of many smaller fires in about 15 to 20 minuets and may last anywhere from 3 to 8 hours. Many parts of the area may remain too hot to enter for a couple of days after the fires have burned themselves out.

Nuclear Weapon Explosion Data (Surface Burst)

Damage Radius Modification Factors for Various Bursts Heights

Crater depths
crater formation will occur when the height of the burst is less than 1/10th of the maximum radius of the fireball.

Subsurface Explosions

All values can be extrapolated for values in between.

Radius M.D. Factors for Ground and Aerial Targets

The following damage factors take Heat and Blast effect in account.

Note: A nuclear Detonation goes out in all directions - up as well as along the ground.

Surface and Air Burst

• TDR - Totally Destroyed
• HDR - 3D6*1,000 M.D.
• MDR - 2D6*100 M.D.
• LDR - Only S.D.C. Inflicted

Note: For aerial targets roll the following percentage additions against the particular skill used to fly the aerial vehicle only if the vehicle survives the initial blast wave. Roll again for the second return blast wave with the same modifications.

• HDR: -90%
• MDR: -70%
• LDR: -40%

If the roll fails, the pilot loses control of the aircraft/mecha, which results in the aircraft tumbling out of the sky and should be role-played to it's fullest.

Sub-Surface Explosion

• TDR - Totally Destroyed
• HDR - 4d6*1,000 M.D. to structures on/under the ground only
• MDR - 3d6*100 M.D. to structures on/under the ground only
• LDR - Only S.D.C. Inflicted to structures on/under the ground only

Breakdown of the Blast Zones

                                     .
                       .                           .

            .                        .                        .
                           .                   .
             [5]                    [4]                    [5]
                                       .
                    .        .               .        .

     .                  .                         .                  .

               .          [3]        _        [3]          .
                    .           .   [2]   .           .
                              .     _._     .
                             .    .~   ~.    .
  .          . [4] .         .[2].  [1]  .[2].         . [4] .         .
                             .    .     .    .
                              .    ~-.-~    .
                    .           .   [2]   .           .
               .          [3]        -        [3]          .

     .                  .                         .                  .

                    .        .               .        .
                                      .
             [5]           .        [4]        .           [5]
                                      .
             .                                                 .

                       .                           .
                                     .
    

Radiation Damage

Radiation damage is permanent and any further exposure is cumulative and is added to the character's total. The following list is the classes of radiation exposure a character is placed in according to their cumulative total. The classes are to be used to determine which character should allow themselves to be exposed to radiation if they are given the choice.

New stat added for game play: Radiation Exposure Class (RC). All starting characters start out with RC-0.

Exposure Classes

Whole Body Radiation Damage from Craters and Fallout

The following table lists the effects of different whole body radiation dosages on humans. The damage resulting from radiation is listed with the convalescent period being the time required to recover from the damage.

Note: Though the damage resulting from radiation can be healed the radiation absorbed is permanent and cannot be "healed"

These doses are immediate or one hour doses, these are strictly worse case possible results. The same dosage acquired over a longer time span would have significantly less drastic effects.

Gaming Penalization for Radiation Levels

Radioactive Contamination Zones in Crater

The most radioactive area would be the bomb crater itself. This area is referred to as Zone 1, and the radioactive level of this zone varies according to the type of burst (see following table). The size of this is equal to the size of the bomb crater itself. Zone 2 is a secondary area of radiation surrounding the bomb crater. The radiation in this zone is only found in craters resulting from surface and subsurface bursts. The size of Zone 2 is equal to the diameter of the bombs fireball. The contamination levels will be very high for several decades after a ground/subsurface burst.

The residual radiation for Zones 1 and 2 are shown below.

Dose Rates

To find any value in between these just divide RADS/Hr by 240 (4 melees per minute x 60 minutes in one hour).

Fallout/Snowout

Fallout follows the t-1.2 law which states that for every sevenfold increase in time after detonation there is a tenfold drop in radiation output.

Example 1. A reading of X level of radioactivity at Y hours after detonation would indicate a level of radioactivity of .1X at 7Y hours after detonation. This is accurate for 2500 hours (14 weeks) following the explosion, thereafter the dose rate is lower than t-1.2 would predict.

Example 2. If a dose rate of 100 RADS/Hr was found at 1 hour after detonation (this assumes all significant fallout from the bomb has fallen, therefore starting with the seven hour point is probably more realistic) would be 10 RADS/Hr at 7 hours, 1 RAD/Hr at 48 hours (2 days), .1 RAD/Hr at 343 hours (2 weeks), .01 RAD/Hr at 2401 hours (14 weeks).

Fallout blows downwind and will fall out at some distance from the explosion. following are examples of various nuclear levels after Y hours percentage population dead exposure to out.

The above examples indicate conditions and exposures that would only be acceptable in wartime. In the examples the wind is continuous in direction and velocity. A real wind would not make such nice neat patterns.

Examples of levels of fallout from a single 1 Mt ground burst with a 24 kph wind.

As a very general rule of thumb, you can expect fallout to move approximately 48 kph. The fallout from a medium-size bomb will extend for several 100's of with the heaviest concentrations within about 325 km of the blast. Areas farther downwind may not receive any fallout for several hours; those closer may get it within fifteen minutes.

The following table shows approximately how long it will take, under normal atmospheric conditions, for fallout to reach the ground at specified distances downwind from a 5 Mt burst.

Fallout usually drifts down over a period of time; it doesn't just plop down all at once. In areas receiving immediate fallout, the particles may continue to fall for a much as 24 hours. Outside the immediate burst area most of the fallout - about 80% of it - will come down within the first 48 hours. Any rain or snow will bring it down even faster and in greater concentrations. Many of the smaller particles may stay in the atmosphere for months or even years.

The following table lists estimated levels of radiation one hour after the detonation of a 20 Mt bomb.

For all practical purposes, radiation levels in excess of a few thousand rads can be ignored. The areas that receive such heavy fallout also will be hit hard by the initial blast and heat.

The following table shows how a starting radiation level of 2000 rads will decay and the total accumulation one can expect as it does so. An area receiving this amount of fallout is likely to be relatively close to a blast site. Figures such as these are not exact. The actual dosages and rates of decay will be altered by local factors such as weather and terrain, but this table does provide a good example.

Areas covered by a given accumulated doses from fallout

These figures are just rough estimations of the actual areas covered.

EMP (Electro-magnetic Pulse)

EMP damage goes out in all directions, to distances greater than that of the effects of the blast itself.

As a general rule of thumb, the distance an EMP will travel is directly related to the height of the burst, the strength of the blast and any natural features in its path.

Rough rule of thumb for the EMP distance covered.

(Height of burst in km x 1000) x (Megatonnage of bomb / 10) = radius of EMP in km

Example:

A 10 Mt bomb detonated at a height of 50 Km.

(50 x 500) x (10/10) = 25000 Km radius

Damage from Pulse

The damage inflicted from the pulse will be to electrical equipment only i.e. computers, radios, telephones, mecha, aircraft, power distribution networks and any other device not hardened from an EMP. The manifestation of this damage will be burnt out electronic components, circuits fried beyond repair etc.

Miscellaneous Notes on Nuclear Explosions

Visibility Distances

The tables shows the distances at which an exposed person would suffer second-degree burns, or at which exposed dark coloured clothing or paint would catch fire. It further shows how these distances are affected by varying visibilities. Distances are in kilometers.

The next table looks at the same effects from weapons detonated at an altitude to maximize blast effects.

19 km visibility is considered an average clear day.
4 km visibility is considered a medium-hazy day.
1.9 km visibility is considered a day of heavy cloudiness.
0.96 km visibility is considered a day of dense cloudiness.

Wind Speeds

The following table gives examples of wind speeds that could be expected at various distances from a 20 Mt explosion.

These figures are approximation, since variables such as terrain and obstructions affect the speeds. The winds will be highest in areas where the land is flat and smooth; hilly terrain or many large buildings will lower velocity. When I say that the winds will be lowered so much that they are no longer be any danger. Rather, the area of danger will simply be decreased somewhat.

Back to Ordnance Netbook main page.

By Chris Curtis (curtis@thepentagon.com).
With help from Mad Dog
and Kitsune (Kitsune@vabch.com).
Copyright © 1997, 1998, 2002 Chris Curtis. All rights reserved.

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NuclearWeapons.php -- Revised: January 27, 2021.