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ASMRB House Rules

Version 1.5
January 9, 2000



17.0 Nuclear Weapons

Nuclear weapons produce three primary immediate damage effects: blast, thermal (flash), and radiation; cratering, radioactive fallout, and firestorms are secondary effects of most nuclear explosions. The following calculations all use these variables:

YExplosive yield equivalent 'Y' expressed in tons of TNT.
RRange from the explosion center, 'R', expressed in meters.
DAtmospheric density 'D' expressed as multiples of standard sea level air density (1.293 kg per cubic meter); if the density is unknown, pressure relative to standard sea level pressure may be used.
AAtmospheric clarity attenuation factor 'A', found on the chart below:
conditions'A' factor
vacuuminfinite
very clear30,000 m
clear10,000 m
haze3,000 m
thin fog1,000 m
fog300 m

Three general types of nuclear weapons are considered here: fission and fission/fusion; pure fusion; and antimatter (CT). All 'real-world' weapons are essentially of the 'fission or fission-fusion' variety. For fission, fission-fusion, and pure fusion bombs a further distinction must be made, based on the yield class of the weapon:

Low Yield:less than 1 kiloton
Medium Yield:greater than 1 kiloton, less than 30 megatons
High Yield:greater than 30 megatons

17.1 Fission or Fission-fusion Devices

The damage classes of various effects are calculated as follows:

damage effect  formula
Blast DCX= 24 + 6/5log2(Y) - 3*log2(R)
Thermal DCT= 22 + 9/10log2(Y) - 2*log2(R) - R/A
Radiation (Hard)[low yield]DCR= 16 + log2(Y) - 2*log2(R) - ((R*D)/200)
 [medium yield] = 16 + 5(Y)0.1 - 2*log2(R) - ((R*D)/200)
 [high yield] = 19 + log2(Y) - 2*log2(R) - ((R*D)/200)
Radiation (Med.) DCR= 18 + log2(Y) - 2*log2(R) - ((R*D)/120)
Radiation (Soft) DCR= 24 + log2(Y) - 2*log2(R) - 2(R*D)

These values can be affected by two further factors: non-standard design or construction, and placement. Total all of the following bonuses which apply:

Design TypeBlastThermHard RadMed RadSoft Rad
neutron enhanced+0 DC+0 DC+3 DC+4 DC+0 DC
radiation enhanced+0 DC+0 DC+2 DC+0 DC+0 DC
fallout enhanced+0 DC+0 DC+1 DC-1 DC+0 + fallout
PlacementBlastThermHard RadMed RadSoft Rad
sub-surface+2 DCnonenonenonenone/fallout
surface+1 DC+0 DC+0 DC+0 DC+0 + fallout
air (<30km)+0 DC+0 DC+0 DC+0 DC+0 DC
high air (<110km)-1 DC-1to10 DC-1 DC+1 DC+0 DC
vacuumnone-10 DC-1 DC+1 DC+0 DC

17.2 Pure Fusion Devices

The damage classes of various effects are calculated as follows:

damage effect  formula
Blast DCX= 24 + 6/5log2(Y) - 3*log2(R)
THermal DCT= 22 + 9/10log2(Y) - 2*log2(R) - R/A
Radiation (Hard)[low yield]DCR= 16 + log2(Y) - 2*log2(R) - ((R*D)/200)
 [medium yield] = 16 + 5(Y)0.1 - 2*log2(R) - ((R*D)/200)
 [high yield] = 19 + log2(Y) - 2*log2(R) - ((R*D)/200)
Radiation (Med.) DCR= 21 + log2(Y) - 2*log2(R) - ((R*D)/120)
Radiation (Soft) DCR= 24 + log2(Y) - 2*log2(R) - 2(R*D)

These values will be affected by placement:

PlacementBlastThermHard RadMed RadSoft Rad
sub-surface+2 DCnonenonenonenone/fallout
surface+1 DC+0 DC+0 DC+0 DC+0 + fallout
air (<30km)+0 DC+0 DC+0 DC+0 DC+0 DC
high air (<110km)-1 DC-1to10 DC-1 DC+1 DC+0 DC
vacuumnone-10 DC-1 DC+1 DC+0 DC

17.3 Antimatter (CT) Devices

The damage classes of various effects are calculated as follows:

damage effect formula
Blast DCX = 23 + 6/5log2(Y) - 3*log2(R)
THermal DCT = 21 + 9/10log2(Y) - 2*log2(R) - R/A
Radiation(Hard)DCR = 23 + log2(Y) - 2*log2(R) - ((R*D)/2000)
 (Med.)DCR = 22 + log2(Y) - 2*log2(R) - ((R*D)/120)
 (Soft)essentially none, as hard and medium radiation is predominant at all ranges

These values will be affected by placement:

PlacementBlastThermHard RadMed RadSoft Rad
sub-surface+2 DCnonenonenonenone/fallout
surface+1 DC+1 DC+0 DC+0 DCnone + fallout
air (<30km)+0 DC+0 DC+0 DC+0 DCnone
high air (<110km)-1 DC-1to10 DC+1 DC-1 DCnone
vacuumnone-10 DC+0 DC+1 DCnone

17.4 Nuclear Weapons - Radiation Effects

The primary, initial emission of radiation from a nuclear explosion consists of gamma rays, neutrons, energetic particles, and X-rays. These are divided into three groups: Hard Radiation: high-energy gamma rays; Medium Radiation: neutrons, low-energy gamma rays; and Soft Radiation: X-rays, beta particles.

All of the radiation damage produced by pure fusion bombs, antimatter bombs, and 'medium' neutron radiation is essentially immediate - the delivery interval is typically measured in milliseconds or microseconds.

For fission and fission-fusion weapons detonated in atmosphere, the 'hard' radiation damage is delivered over a short (but not instantaneous) period of time. Characters exposed for more than 1/2 of the interval in which high-energy gamma rays are being produced will receive the damage listed above. The hard radiation exposure interval is:

exposure interval, seconds = (Y)0.5 / 200

This will be modified by the placement of the bomb:

PlacementTime Factor
sub-surfacen/a
surfacex 1.414
air (<30km)x 1
high air (<110 km)x 0.1
vacuumx 0

Characters who can obtain cover in some fraction of this time will take one less DC for each halving of their exposure time. One suggested game mechanic for determining the delay in obtaining cover is to require the character to make a DEX roll, with the 'Diving for Cover' distance modifiers; making the roll exactly results in the character getting 'under cover' in 1 second, halved for each 2 points the roll is made by. Gamma radiation from fission and CT bombs is 'prompt,' i.e. no significant delay occurs between detonation and full exposure.

Example: Commander Thomas and CPO Michellin are standing in the open at roughly sea level after firing a 'Davy Crockett' M388 nuclear weapon at a surface target 500 meters away. The weapon is a fission device with a yield of 1000 tons; at this range the medium radiation is rated at DC 6; the bomb produces hard radiation with a DC of 6 also. No soft radiation is experienced at this range. The hard radiation exposure interval is essentially instantaneous. The target is subjected to a Damage Class 36 blast, and Damage Class 34 `soft' radiation (obviously, soft is a relative term).

Protection from 'hard' radiation is afforded primarily by mass: every 300 kg per square meter will reduce radiation damage by 1 DC. Protection from 'medium' radiation is gained at -1 DC per 200 kg per square meter. Protection from 'soft' radiation and residual radiation (i.e., fallout: low-energy gamma rays, beta particles and alpha particles) is gained at -1 DC per 100 kg per square meter. Note that this protection increases linearly, and rounds in ordinary fashion.

Example: the turret roof of the T-72 tank weighs about 280 kg per square meter, and thus has protective values of -1 DC vs. hard radiation, -1 DC vs. medium radiation, and -3 DC vs. soft radiation. Note that this does not include the effect of the neutron-absorbent anti-radiation liner.

After all protective conditions have been applied, apply only the radiation damage (either hard, medium, or soft) with the highest remaining damage class; if two classes are equal, apply radiation damage of +1 DC over either one.

Example: as the 'Davy Crockett' bomb produces DC 6 gamma radiation damage and DC 6 neutron damage at 500 meters range, both Commander Thomas and CPO Michellin will take DC 7 radiation damage.

Some sample protection values are:

protection structure hardmediumsoft
Morrow Project 'Mars' vehicle -3 DC -11 DC-9 DC
tank:M60-2 DC -8 DC-5 DC
 M48A2-1 DC-2 DC-4 DC
Commando V-150 -1 DC-1 DC-2 DC
M113A1 armored personnel carrier -0 DC-1 DC-1 DC
multistory building:upper floor-2 DC-3 DC-6 DC
 ground floor-1 DC-2 DC-3 DC
frame building:ground floor-0 DC-0 DC-0 DC
 basement-1 DC-2 DC-3 DC
foxhole -1 DC-2 DC-3 DC
shelter w/1m earth cover -2 DC-12 DC-6 DC

Note that some of these example protection values do not match the results obtained with the above guidelines, due to neutron absorbing liners; the subject of radiation protection will be covered in more detail at some future time, when a more complete coverage of atmospheric transmission, scattering effects, and fallout will be produced by the ASMRB.

It is important to remember that nuclear radiation is scattered by the atmosphere and by contact with objects; therefore, characters must be nearly entirely enclosed by protective structures or devices in order to be protected.

The effect of radiation damage on characters is summarized on the Radiation Effects chart. The direct immediate radiation damage should be rolled as 'normal' dice. The Stun portion of this damage is applied immediately; characters may apply the better of their PD or ED to this portion of the damage. For game purposes, the Body portion of this attack is applied after the period of time listed under 'BOD Delay,' with no defense, and a x2 Body Multiplier (it is assumed to affect the 'Vitals'). Note that the Stun taken by the character may not be less than the final amount of Body lost.

The long term effects of radiation damage are simulated by reducing the Characteristic Maximums; this reduction occurs (for game purposes) after the listed 'Stat Delay,' and is (usually) permanent. The same die rolls should be used for both the direct Body damage and the reduction in characteristic maximums. As a note, the U.S. Army considers 50 rads or so to be a 'war emergency only' dose; 1000 rads is considered a pretty sure thing lethal dose, with a 99% death rate. All medical effects associated with lesser dosages will also experienced at higher dosages.

Example: both Commander Thomas and CPO Michellin have taken DC 7 radiation damage from their 'Davy Crockett' bomb. Both have a BOD and CON of 18 normally, a PD of 8, and 36 Stun. After 15 minutes, each will take a 7d6 attack. Thomas takes 6 Body and 18 Stun, which becomes 12 Body and 12 Stun; Michellin takes 7 Body and 26 Stun, which becomes 14 Body and 18 Stun. Michellin thus is Stunned but not unconscious.

Commander Thomas has also taken 8 Body from thermal damage (see section 12.5); thus he is at -2 BOD! Quick paramedic work by CPO Michellin soon stops Mr. Thomas from losing Body on post-segment 12; within a few hours Thomas is in a major hospital.

After 3 days in the hospital, Thomas has regained 3 Body due to medical treatment, and is at 1 BOD (missing 17 out of 18 BOD); at this time, the Stat reductions are applied. The important one here is the BOD reduction: an 18 was rolled, bringing his maximum BOD to 2. From BOD 2 to BOD 10 all characters spend 16 points; Thomas has spent an additional 16 to get his original BOD of 18. Thus his current BOD is (32 / 4) + 2 = 10. As Thomas is still down 17 Body, he is barely (just barely) alive, at 7 below Ø.

Also in the hospital, Chief Michellin has also recovered 3 Body, and is still down 9 points. Due to the damage class 7 attack, Michellin suffered a 26 point reduction in his BOD Maximum, to -6; there were 48 points 'spent' above this originally on the character's BOD of 18. (48 / 4) + (-6) = 6, Michellin's new BOD characteristic value. As he is still suffering from 9 points of damage, he also is barely alive, at 3 below Ø.

Note that immediate treatment with anti-radiation drugs might have reduced the radiation DC the boys suffered.

17.5 Nuclear Weapons - Thermal Effects

The thermal portion of nuclear explosion damage is caused by intense visible and infrared radiation.

The thermal damage occurs over a short (but not instantaneous) period of time when nuclear weapons are detonated within the atmosphere (in a vacuum, no delay is experienced with any type of nuclear weapon). Characters exposed for more than 1/2 of the interval in which the thermal effect is being produced will receive the full damage. The thermal exposure interval is derived as:

exposure interval, seconds = (Y)0.5 / 200

This will be modified by the placement of the bomb:

PlacementTime Factor
sub-surfacen/a
surfacex 1.414
air (<30km)x 1
high air (<110 km)x 0.1
vacuumx 0

Characters who can obtain cover in some fraction of this time will take one less DC for each halving of their exposure time. One suggested game mechanic for determining the delay in obtaining cover is to require the character to make a DEX roll, with the 'Diving for Cover' distance modifiers; making the roll exactly results in the character getting 'under cover' in 1 second, halved for each 2 points the roll is made by. Of course, modifiers for surprise may also be appropriate.

Example: Commander Thomas, watching his 1 kiloton fission device explode on a surface target 500 meters away on a clear day, is exposed to a DC 13 thermal effect. The flash exposure interval is about 0.22 seconds. Chief Michellin, his assistant (DEX 18), dives for cover behind their jeep, and based on the player's roll of 11, the character gets 'covered' in under 0.5 seconds. As this is still more than 1/2 of the exposure interval, Chief Michellin is also exposed to DC 13 of thermal effect. The jeep itself, of course, is exposed to the full DC 13 thermal effect.

Protection from thermal effects can be determined by combining the following protection factors (T-DEF); note that, unlike other forms of armor in the Hero System, thermal damage protection is an 'all or nothing' situation: if any Body gets past the protection, then the target character takes all the Body (and Stun) of the attack, as a Normal Energy attack, against the 'worst' exposed area. However, location modifiers to Body and Stun are not used.

materialvariantprotection value
Armor:use 15 + 1/3 of 'normal' DEF, with modifiers for Water Content & Color only
Fabric Thickness:sheer9 T-DEF
 thin (summer shirts)10 T-DEF
 medium (shirts, summer pants)11 T-DEF
 thick (pants)12 T-DEF
 each x2 thickness+1 T-DEF
Fabric Material:normal (cotton, wool, rayon, etc.)+0 T-DEF
 synthetics (nylon, polyester, etc.)-1 T-DEF
 modern synthetics (gore-tex)+1 T-DEF
 flameproofed (treated fabric)+1 T-DEF
 fireproof (asbestos, nomex)+2 T-DEF
Fabric Weave:fine ('satin')-1 T-DEF
 coarse ('canvas')+1 T-DEF
Water Content:damp+1 T-DEF
 soaked+2 T-DEF
Color:black (dark gray)+0 T-DEF
 dark (blue denim, olive drab)+1 T-DEF
 medium (tan, red)+2 T-DEF
 light (beige, pink)+3 T-DEF
 white (cream)+4 T-DEF
 silver+5 T-DEF

Other conditions can increase or reduce the damage class of the thermal attack, if the T-DEF is 'penetrated':

factor DC mod
Exposure:full body-0 DC
 1/2 (one side or upper half)-1 DC
 1/4 (head and/or arms and/or legs)-2 DC
 1/8 (arm or leg or hands or feet or head)-3 DC
 1/16 (hand or foot)-4 DC
Skin Color:dark (African)-0 DC
 light (Asian, European)-1 DC
Sizeeach x2 human size (1 square meter)+2 DC

Example: when exposed to the flash of the 'Davy Crockett' bomb, both Commander Thomas and CPO Michellin are exposed to DC 13 thermal flash. Thomas is wearing tropical fatigues, not damp or soaked, and is fully exposed; his skin is light colored. Medium cotton fabric in olive drab color is T-DEF 11 against thermal effects; as this is less than the DC 13 thermal attack, he will receive no defense from the clothing, which bursts into flame. However, his light skin color reduces the damage he takes by 1 DC, to DC 12; after applying his ED of 8 he takes 4 Body.

Commander Thomas's assistant, CPO Michellin, is wearing a fire-fighter's suit, fabricated of aluminum coated asbestos. This thick, coarse, silver-colored material provides Michellin with 20 T-DEF against thermal flash; he takes no damage from the DC 13 flash. If Michellin were not wearing the helmet portion of the fire-fighter's suit, he would have been exposed to 13 DC, -3 for head exposed only, -1 for light skin, for 9 DC against his ED of 6; thus 3 points of Body would be taken by the character.

Nuclear flash blindness, temporary or permanent, can be produced by the thermal effect of nuclear explosions. Characters in the open (whether or not they are looking towards the nuclear detonation) receive a negative modifier to visual perception rolls equal to twice the DC of the thermal damage they take. This modifier will be temporary, with a duration of a few hours or days, unless the character is actually observing the explosion directly. If produced by direct observation, nuclear flash modifiers are permanent. Permanent perception rolls of zero or less indicate total eyeball damage.

'Flash Protection' (as the Hero System power) will reduce the damage class for flash blindness purposes. The reduction in damage class for vision protective items is proportional to the base 2 logarithm of the transmission factor (1 minus the reflectivity). A few examples of eye protection are given for comparison purposes:

protection typeprotection factor
sunglasses:-1 to -3 DC
welder's goggles or masks:-10 DC
SAC crew goggles:-10 DC

If vision protection items are combined, their protective values are added directly together.

Example: Commander Thomas, observing his 1 kiloton fission device detonating, has been exposed to DC 13 thermal damage. He has a pair of aviator sunglasses (-2 DC) for eye protection, and is specifically watching the blast; he takes a -22 to his visual perception roll. As his normal perception roll was 13-, the referee rules his eyes will (within a few hours) shrivel up and fall out; he is totally, immediately, and permanently blind.

CPO Michellin, who is not looking directly at the blast, is wearing the gold-tinted visor of his aluminum coated asbestos fire-fighting suit (-2 DC), and a pair of tinted welder's goggles (-10 DC), for a net -12 DC against flash blindness. He therefore receives only DC 1 for flash blindness purposes, and will be -2 on visual perception rolls for a short while.

17.6 Nuclear Blast Effects

Nuclear blast is treated as a normal explosion per Section 16.21; the blast damage can be reduced by the protection modifiers given in that section - always assuming that any protective structures themselves are not destroyed by the explosion.

Note that the radius of the perceptible fireball in a standard atmosphere is equal to the damage class 20 distance from the explosion.

The delay period between the instant of detonation and the arrival of the first blast wave, at sea level on Earth, is found by:

delay time, seconds = R / 330 meters/second

Example: Commander Thomas is still standing in the open after firing the 'Davy Crockett' nuclear weapon at a target 500 meters away; CPO Michellin is by now crouched behind their jeep. The weapon is a fission device with a yield of 1000 tons. Thomas will take 9d6 normal damage from the blast effect, which will arrive about 1.5 seconds after detonation; rolling for the damage produces 10 Body and 32 Stun. Thomas has a PD of 12, and takes Ø Body and 20 Stun. Michellin, crouched with half cover, takes only 6d6 damage. The 'Davy Crockett' produces a fireball with a 40 meter radius.


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Document last modified Friday, June 01, 2001