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

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.

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.

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


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.


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.


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)

Yield Crater
5 Kt 0.068 0.084 0.469 0.678 1.042 1.303
10 Kt 0.085 0.111 0.591 0.919 1.313 1.642
20 Kt 0.108 0.146 0.745 1.158 1.655 2.608
50 Kt 0.146 0.211 1.011 1.572 2.246 2.807
100 Kt 0.184 0.278 1.273 1.981 2.830 3.537
200 Kt 0.232 0.368 1.604 2.495 3.565 4.456
300 Kt 0.265 0.433 1.836 2.857 4.081 5.101
500 Kt 0.315 0.531 2.177 3.387 4.838 6.048
1 Mt 0.396 0.700 2.743 4.267 6.096 7.620
2 Mt 0.499 0.924 3.456 5.376 7.680 9.601
3 Mt 0.572 1.087 3.956 6.154 8.792 10.980
4 Mt 0.629 1.219 4.355 6.774 9.677 12.096
5 Mt 0.678 1.333 4.691 7.297 10.424 13.030
8 Mt 0.792 1.609 5.486 8.534 12.192 15.240
10 Mt 0.854 1.759 5.910 9.193 13.133 16.417
20 Mt 1.076 2.322 7.466 11.583 16.547 20.684
25 Mt 1.159 2.538 8.021 12.477 17.825 22.281
30 Mt 1.231 2.730 8.524 13.259 18.942 23.677
40 Mt 1.355 3.063 9.382 14.594 20.848 26.060
50 Mt 1.460 3.349 10.106 15.720 22.458 28.072
100 Mt 1.839 4.420 12.733 19.807 28.295 35.369
150 Mt 2.105 5.198 14.575 22.673 32.390 40.487
Kt = kiloton (1 Kt = 1000 tons = 2 million lb.)
Mt = megaton (1 Mt = 1000 kilotons = 2 billion lb.)
Note: All measurements are in kilometers.

Damage Radius Modification Factors for Various Bursts Heights

Subsurface Explosion (-100 meters) x0.80   x0.80 x0.80 x0.80 x0.80
Extra Low Air burst (600 meters)   x3.00 x3.00 x3.00 x3.00 x3.00
Low Air burst (2.5 kilometers)   x3.50 x3.50 x3.50 x3.50 x3.50
Medium Air burst (5.3 kilometers)     x4.00 x4.00 x4.00 x4.00
High Air burst (10 kilometers)     x4.50 x4.50 x4.50 x4.50
Extra High Air Burst (25 - 30 kilometers)     x0.75 x1.00 x3.00 x6.00
Outer Atmosphere Burst (Above 30 kilometers).
No significant damage done, EMP is the most destructive effect of this type of detonation.

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

surface explosions and low air bursts
1 mt 36.576 meters
10 Mt 60.960 meters
100 Mt 100.584 meters

Subsurface Explosions

Subsurface Explosions
1 Mt 88.392 meters
10 Mt 131.064 meters
100 Mt 192.024 meters

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

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.

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

Breakdown of the Blast Zones

                       .                           .

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

     .                  .                         .                  .

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

     .                  .                         .                  .

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

                       .                           .
Diagram Outline
[1] Vaporization Point (Crater) Everything is vaporized by the blast.
[2] Total Destruction All structures above ground are destroyed.
[3] Severe Blast Damage Factories and other large-scale buildings collapse. Severe damage to highway bridges. Rivers sometimes flow counter-current.
[4] Severe Heat Damage Everything flammable burns. People in the area suffocate due to the fact that most available oxygen is consumed by the fires.
[5] Severe Fire & Wind Damage Residency structures are severely damaged. People are blown around. 2nd and 3rd-degree burns suffered by most survivors.

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

Class Exposure (in RADS) Risk
RC-0 0 Exposure May take normal risks
RC-1 0< RADS <=70 Should avoid further exposure
RC-2 70< RADS <=150 Should not risk any further exposure
RC-3 150 + Only in absolute emergency should any further exposure be risked

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"

Dosage in RADS Incidence of Vomiting Convalescent Period Effects
0-25 0% N/A Practically no "short-term" effects. May be some blood cell damage.
26-100 5% 7 Days A small amount of nausea and sickness for highest dose level. Blood changes noticeable.
101-200 100% Up to 40 Days Definite identifiable changes in blood cells. Highest dose causes hair loss, livid skin spots, nausea, vomiting, diarrhea, fevers, hemorrhages and great fatigue. Heart failure in some.
201-400 100% Several weeks Symptoms as above but more to months, severe Fatal to 25% in low range, 50% in high range.
401-600 100% Death Symptoms as above but now very and occurring soon after exposure. Death will occur within 1D6 days.
601-800 100% Death Symptoms as above but circulatory system and parts of the central nervous system malfunction rapidly. Death will occur in 1D6 hours.
801-5000+ 100% Death Outcome very rapid. Vomiting, falling blood count, diarrhea, great fatigue, internal bleeding, organ failure, nervous system collapse heart failure, coma, and then death.

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

RAD Level Penalty
0-25 None
26-100 P.S. -1, P.P. -1, P.E. -1
101-200 P.S. -2, P.P. -2, P.E. -2, P.B. -2, P.P.E. -10
201-400 P.S. -3, P.P. -3, P.E. -3, P.B. -3, P.P.E. -20
401-600 P.S. -5, P.P. -5, P.E. -5, P.B. -5, P.P.E. -40
601-800 P.S. -7, P.P. -7, P.E. -7, P.B. -7, P.P.E. -50
801-5000+ P.S. -15, P.P. -15, P.E. -15, P.B. -15, P.P.E. -100
The above effects are permanent and cannot be modified by normal means.

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.

Subsurface Burst Surface Burst Air Burst High Air Burst
Zone 1 8000 RADS/Hr 6000 4000 2000
Zone 2 4000 RADS/Hr 3000 N/A N/A

Dose Rates

10000 42
9000 37
8000 33
7000 29
6000 25
5000 21
4000 17
3000 12.5
2000 8
1000 4
500 2
100 0.4
50 0.2
25 0.1

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


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.

Time RADS/Hr Death Percentage in population
An area 16 Km wide by 48 Km downwind from a single 1 MT ground burst
1 Hr. 1,000 100% dead at 1 hour of exposure
7 Hours 100 50% dead within 7-8 hours of continuous exposure
2 Days 10 50% dead for 5 days of continuous exposure
2 Week 1 50% dead for 1 month continuous exposure
14 Weeks 0.1 0% dead from radiation hereafter
An area 19 Km by 152 Km downwind for a single 1 MT ground burst
1 Hr. 0 Radiation has not arrived yet
7 Hrs. 50 50% dead for 18 hours of continuous exposure
2 Days 5 5% dead for 2 weeks of continuous exposure
2 Weeks 0.5 0% dead from radiation hereafter
14 Weeks 0.05 0% dead from radiation hereafter

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.

Distance from Blast Fallout Will Begin After
8 Km 20 Minutes
40 km 1 Hour
160 Km 3-5 Hours

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.

Distance from Blast Radiation Level
8-24 km 10000-1000
24-120 Km 1000-100
120-193 km 100-0

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.

Time Interval Interval Dose Cumulative Dose
1st-2nd hour 2000 2000
2nd-3rd hour 1000 3000
3rd-4th hour 640 3640
4th-5th hour 440 4080
5th-10th hour 1200 5280
10th-24th hour 1200 6480
2nd day 760 7240
3rd day 400 7640
4th day 240 7880
5th day 180 8060
6th day 140 8200
7th day 96 8296
2nd week 430 8726
3rd week 230 8956
4th week 110 9066
2nd month 175 9241
3rd month 80 9321
4th month 50 9371
5th month 30 9401
6th month 20 9421
6th-12th month 50 9471
2nd year 16 9487
3rd year 5 9492
4th year 3 9495

Areas covered by a given accumulated doses from fallout

Upper Limit of Accumulated Dose Area (Km2)
RADs 1 Mt 10 Mt
1000 900 11000
800 1200 14000
600 1700 18000
400 2600 27000
200 5500 52000
100 10500 89000
50 18600 148000
25 32700 234000
10 56000 414000

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


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.

Visibility (km) Size of bomb (Mt)
1 5 10 20 50 100
16 10 18 21 24 26 28
48 11 22.5 26.5 29 35 42
80 14 27 33 42 52 61

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

Visibility (km) Size of bomb (Mt)
1 5 10 20 50 100
19 14 29 40 51 76 98
4 10.5 22.5 29 39 61 80
1.9 4.5 10 13 19 26 30.5
0.96 0.5 3 4 6.5 11 18

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.

Distance (km) Surface Burst (kph) Optimum Air Burst (kph)
3.2 2333 3138
4.8 1046 2253
8 483 684
16 177 321
24 88.5 185
32 56 121
48 30.5 72.5
80 14.5 32

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.