Explosions

Explosions

Certain attacks, such as hand grenades and Explosive Fireball spells, produce a blast when they hit. Such attacks have the notation "ex" after their damage type: "cr ex” for a crushing explosion, "burn ex" for a burning explosion, and so on.

In addition to doing the listed damage to whoever was struck directly, an explosion inflicts "collateral damage" on everything within (2 × dice of damage) yards. For instance, if an explosion does 6d×2 damage, everyone within 24 yards is vulnerable – although some might be lucky enough to take little or no damage.

The listed damage only applies "as is" to the target struck. For everything else caught in the blast, roll this damage but divide it by (3 × distance in yards from the center of the blast), rounding down. Roll damage individually (but the GM can save time by using one roll for several NPCs). Use torso armor to determine DR against explosion damage.

If an explosive attack has an armor divisor, it does not apply to the collateral damage. For example, the shaped-charge warhead of an anti-tank rocket has an armor divisor of (10), but this only reduces the DR of a target it actually strikes; those nearby get their full DR against the blast.

Explosions are considered incendiary attacks, and can start fires; see Catching Fire.

Anyone caught in a blast may attempt an active defense roll to dive for cover from the explosion's collateral damage and fragmentation; see Dodge and Drop.

Explosions in Other Environments

Other Atmospheres: These rules assume Earth-normal air pressure. A thicker or thinner atmosphere enhances or reduces the blast effect. Underwater, divide collateral damage by range in yards instead of 3 × range in yards. In a vacuum or trace atmosphere, with no medium to carry the shockwave, damage comes only from the expanding gases themselves: divide damage by 10 × range in yards.

Contact Explosions: A person can throw himself on a grenade, etc. to protect his friends; see Sacrificial Dodge and Drop. He takes maximum possible damage; his DR protects him normally. Everyone else gets his torso's DR + HP as "cover DR."

Internal Explosions: If an explosive goes off inside someone – e.g., a follow-up attack penetrates the target's DR, or a dragon swallows a hand grenade – DR has no effect! In addition, treat the blast as an attack on the vitals, with a ×3 wounding modifier.

Fragmentation Damage

Many grenades, bombs, and artillery shells have metal casings designed to shatter when they explode, producing a storm of sharp fragments. Some are packed with extra material (pellets, nails, etc.) to enhance this effect.

Fragmentation damage, if any, appears in brackets after explosive damage; e.g., "[2d]" means 2d fragmentation damage. Everyone within (5 × dice of fragmentation damage) yards is vulnerable. For example, that [2d] attack would throw fragments out to 5 × 2 = 10 yards.

The farther a target is from the blast, the less likely the fragments are to hit him. A hit is automatic if the explosive attack actually strikes the target. The fragments attack everyone else in the area at skill 15. Only three modifiers apply: the range modifier for the distance from the center of the blast to the target, the modifier for the target’s posture (prone, etc.), and the target’s Size Modifier. It is possible for several fragments to hit! For every three points by which the attack roll succeeds, one additional fragment strikes the target.

The only active defense against fragments is to dive away from the explosion that produced them; see Dodge and Drop.

For each hit, roll hit location randomly. If that location is behind cover, the fragment hits cover.

Fragmentation damage is cutting. Note that if an explosive attack has an armor divisor, this does not apply to the fragments it produces.

Airbursts: Against an airburst, do not apply posture modifiers – lying prone under an airburst does not decrease the body area exposed to the rain of fragments! Only overhead cover protects.

Incidental Fragmentation: An explosion with no listed fragmentation damage can still create fragments if there is any loose or frangible material at the explosion site. Incidental fragmentation damage ranges from 1d-4 for ordinary earth to 1d for an explosion on loose scrap.

Hot Fragments: White phosphorus -type smoke warheads produce this effect. The fragments typically inflict 1d(0.2) burning damage every 10 seconds for one minute.

Demolition

Sometimes the only way to deal with a problem is to blow it up! If the adventurers are using or facing explosives, the PCs or GM should decide how many dice of damage – in multiples of 6d – the blasting charge is supposed to do, and what kind of explosive it is.

Explosives normally do crushing damage with the Explosion modifier – and often the Fragmentation modifier.

How Much Explosive? An explosion doing 6d×n damage takes (n×n)/4 pounds of TNT. If you are using an explosive other than TNT, divide the weight required by its relative explosive force (REF) – see the Relative Explosive Force Table, below.

How Big a Blast? Reverse the formula to determine how much damage a given weight of explosive will do: damage is 6d × square root of (weight of explosive in lbs. × 4 × REF).

Example: A 1920s Chicago safe-cracker plans to blast through a bank vault. Estimating the toughness of the vault, he decides he needs a blast that does 6d×8 damage. He's using dynamite. The weight of dynamite he needs is (8 × 8)/(4 × 0.8) = 20 lbs.

Relative Explosive Force Table

TL	Type	REF	Description
3	Serpentine Powder	0.3	Standard gunpowder, pre-1600.
4	Ammonium Nitrate	0.4	Common improvised explosive.
4	Black Powder	0.4	Standard gunpowder, 1600-1850.
5	Black Powder	0.5	Standard gunpowder, 1850-1890.
6	Diesel Fuel/ Nitrate Fertilizer	0.5	Common improvised explosive.
6	Dynamite	0.8	Commercially available for mining, demolition.
6	TNT	1.0	The basic, stable, high explosive.
6	Amatol	1.2	TNT-ammonium nitrate. Fills bombs & shells in WWII.
6	Nitroglycerine	1.5	Unstable! If dropped, detonates on 13+ on 3d.
7	Tetryl	1.3	Common for smaller explosive shells and bullets.
7	Composition B	1.4	Another common explosive filler.
7	C4 Plastic Explosive	1.4	Standard military and covert-ops explosive.
9	Octanitrocubane	4	Theoretical advanced explosive.
10	Stabilized Metallic Hydrogen	6	Exotic science-fiction explosive.

Nuclear Weapons (High-Tech) (TL7+)

Nuclear weapons, an early TL7 development, derive their immense destructive power from nuclear fission or fusion. The energy released by a nuclear explosion takes the form of a thermal pulse (heat), concussion, hard radiation, and – in a low-altitude burst – residual radiation (fallout). A nuclear device thus inflicts crushing damage with the explosion (ex) modifier, linked to burning damage with the explosion, radiation (rad), and surge (sur) modifiers; see Damage Modifiers. Divide burning damage by only (2 × distance in yards from center of blast). Flash and Blindness always applies!

It's customary to rate a nuclear weapon's yield in terms of the quantity of TNT to which it's equivalent. This is usually expressed in kilotons (thousands of tons of TNT) or megatons (millions of tons). Nuclear explosives don't appear on the Relative Explosive Force Table, though, because most of a nuclear device's weight is that of the detonator, not the explosive.

The first atomic bomb used in war was a fission device named "Little Boy." Released over Hiroshima, Japan on August 6, 1945, it devastated the city with the equivalent of 12,500 tons of TNT, or 12.5 kilotons (6d×10,000 cr ex with 6d×6,500 burn ex rad sur linked). The hydrogen bomb, developed in the mid-1950s, further refined the art of destruction. Properly known as a thermonuclear device, this two-stage weapon employs a fission bomb to provide the incredible heat necessary to fuse hydrogen. The yield can approach 100 megatons – well beyond what fission can accomplish. At the other end of the spectrum, compact, modest-yield nuclear weapons become possible at mid-TL7. The U.S. and Russia produced miniaturized warheads weighing 50-100 lbs., with yields of about 0.1 kiloton (6d×900 cr ex with 6d×650 burn ex rad sur linked).

EMP

Unshielded electronic equipment within the visual horizon of a nuclear explosion risks a surge effect that can incapacitate it. This side effect of a nuclear blast is termed electromagnetic pulse (EMP). The larger or more numerous the bombs, the greater the EMP; for example, a 10-megaton nuclear detonation 200 miles above the center of the continental U.S. would blanket the entire country in its pulse.

Treat EMP as an Affliction that only affects electronics and those who have the Electrical disadvantage. This effect is distinct from the surge modifier on the explosion's burning damage! Every vulnerable target in the radius of the EMP suffers a HT-8(2) aff attack. A failed resistance roll means that item is knocked out of action until repaired. Affected solid-state technology is likely to be permanently damaged: all repair rolls are at -10. Repairs on other devices are at only -4.

A variety of TL7-8 military hardware is shielded entirely against EMP. Fiber-optic systems are also immune. Other equipment can be protected by surrounding it with metal that is in turn grounded.

Fallout

Residual radiation – better known as "fallout" – consists of material picked up, irradiated, and spread around by a nuclear explosion. It's generally only a factor in a "ground burst," where the nuclear weapon's fireball touches the ground. When it does occur, though, the radioactive debris distributed by the mushroom cloud poses a serious threat to anyone passing through or downwind of the blast site.

In game terms, assume that the contaminated "footprint" is an area 800 yards long by 200 yards wide, drifting downwind, for a 0.1-kiloton nuke. Double length and width for each tenfold increase in yield! Everything in this zone suffers radiation damage, measured in rads. Individuals passing through soon after the detonation are exposed to 100 rads per hour. This drops to 10 rads per hour about two days after the explosion, and to 1 rad per hour some two weeks afterward. For effects, see Radiation.

Building a Nuclear Device

Realistically, designing and building a nuclear weapon requires a team of dozens of diverse specialists, several years, and the financial resources of a small country. In a cinematic game, though, a lone gadgeteer might be able to create a "home-made" nuke. Treat this as an Amazing invention that requires the Engineer (Nuclear) skill and several pounds of weapons-grade fissionables. Since such materials are almost never available on the open market, the inventor will likely have to steal them ... or develop a working enrichment process that allows him to manufacture his own, which is a separate Amazing invention!