Explosions

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Explosion Animation

General Rules

Explosions are confined to one level. They do not affect any other level (even if there is no obstruction) no matter how strong the explosive power of the detonation. The explosion will also be applied to FLOOR tiles on the level above the blast but it does not affect any units or objects (including non-floor terrain tiles, such as walls) on those particular tiles.

Explosive Damage to Walls and Objects

Explosions differ from weapons in a couple of important ways.

  1. First, of course, they are area-of-effect. (Duh.)
  2. Second, they impart Damage within a narrower interval than weapons. Weapons impart from 0 to 2 times their rated strength. (In other words, the UFOpaedia is showing you their average strength.) Explosives also impart the average listed damage from the UFOpaedia, but they have a minimum of average/2 and a maximum of 3/2*average. So a blaster (HE 200) does from 100 to 300 damage at ground zero (GZ). You will still receive the damage listed in the UFOpaedia at GZ, on average. But you are guaranteed to get some damage if caught within its blast radius, unlike a firearm, which will hit you (if it hits!) for 0 to 2x damage, regardless of range. Of course, if your armor is high enough relative to the damage roll, it always blocks any actual damage.

Average explosive damage to units decreases by 10 per tile away from GZ. At the same time, the maximum damage is decreasing by 15 (3/2*10) and the minimum damage by 5 (10/2). Thus at GZ of a grenade blast (HE 50), units receive 25-75 damage, and at its outer edge (radius=5 tiles from GZ), units receive 5-15 damage.

Unlike for units, explosive damage to non-units (ground, walls, and objects) is constant. Thus a specific explosive will always form the exact same blast pattern on the same type of terrain. It is calculated based on the minimum damage (i.e., average/2) for a given square. Thus it starts (at GZ) as half average damage and decreases by 5 per tile outward. If this value is greater than tile armor strength, the tile will be destroyed. However, a given type of explosive always has the same blast radius, regardless of terrain effects (except if there is blockage by e.g. walls). A Blaster can still kill you when 11 tiles away, even if you're on hard UFO floors which will only be damaged four tiles from GZ.

HE Statistics

Here's a table of explosive strength and resulting expected blast damage and radii.

                     HE @ Ground Zero      Blast           HE @ Edge 
  Type               Min   Ave    Max   Diam. Rad. Disc. Min  Ave   Max
  AC - HE            22     44     66      7    3   0     7    14    21
  Grenade            25     50     75      9    4   0     5    10    15
  HC - HE            26     52     78      7    3   1    11    22    33
  Proxy              35     70    105     13    6   0     5    10    15
  Small Rocket       37.5   75    112.5    9    4   2    17.5  35    52.5
  Rocket Tank        42.5   85    127.5   11    5   2    17.5  35    52.5
  Alien Grenade      45     90    135     13    6   2    15    30    45
  Large Rocket       50    100    150     13    6   3    20    40    60
  Hi - EX            55    110    165     13    6   4    25    50    75
  Fusion Hovertank   70    140    210     23   11   2    15    30    45
  Blaster Bomb      100    200    300     23   11   8    45    90    135
  • HE @ Ground Zero is damage to units at ground zero (GZ). Min=Ave/2, Max=Ave*3/2.
  • HE @ Edge is damage at the edge of the blast.
  • Blast Diameter includes GZ. Equals 2r+1.
  • Blast Radius does not include GZ. Equals (d-1)/2.
  • Disc is the discrepancy between actual radius, and the radius expected based on HE. Higher explosives have their blast size 'nipped'. Otherwise the Blaster would have a diameter of 39 - almost 4 tilesets wide!

Average damage to units falls off by 10 per tile away from GZ. Damage to tiles is fixed at half the damage for that tile (i.e., the minimum damage that units can receive) and decreases by 5 per tile (half the 10, that the average is decreasing). Note that damage is still done to units at the stated radii, even if blast strength was not strong enough to damage tiles. That is, you can still be hurt even past where you see floor damage. This is especially true in UFOs and alien bases, which have very strong tiles (see Blast Diameters and Tile Characteristics). Even the mighty Blaster only hurts UFO floor tiles (armor=80) out to four tiles from GZ, but your men can still be killed 11 tiles away, regardless. Also note, floor damage does not "soak up" any of the blast. However, some tiles (especially wall tiles) have an "HE Block" value which does prevent some damage from being passed on. This is what keeps blasts from acting as if walls didn't exist.

Because damage to tiles is fixed, they always produce the same blast pattern for a given type of terrain. Terrains differ in their "armor" (a.k.a. constitution) levels, and are destroyed if the blast damage is equal to or greater than their armor. Most ground terrain also has a second "damaged" tile which appears when the first tile is destroyed. This second tile (a.k.a. death tile) may also be destroyed by the blast, if the blast strength is equal or greater then the armor for both tiles. Raw earth is left if all ground tiles are destroyed. Some tile sets (such as arctic) have the second death tile set to such a high armor value (255) that no blast will destroy it; thus you'll never see raw earth right under the surface of ice(!). For what it's worth, you can calculate the tile armor simply by looking at the blast pattern and comparing the HE strength (dropping of by 5 at center) to the point where tiles are no longer damaged.

Example: On a desert map, a prox mine will make a pattern with damaged tiles out to a radius of 6. The 9 innermost tiles (radius=1) will show a different tile (blown to raw earth). The first tile in desert has armor of 5 (thus, it's damaged all the way to edge of blast) but the second "dimpled" tile seen after the first one is blown through, has armor of 25. The prox mine is HE 70, so it's hitting ground zero for 35 and GZ+1 for 30. Thus it blows through to raw earth out to GZ+1 (5+25=30).

You may also see additional terrain damage with subsequent explosions. Example: the humble grenade (HE 50) damages the first tile (armor=5) out to radius=5, but does not break through the second tile (armor=25) to raw earth. But a second grenade in the same place will break through the injured tile at GZ, because now that the top tile is gone, the second tile is exactly equal to half grenade strength, right where it exploded.

Blast Propagation

As an example of a progressing blast front, Blaster Bombs impart damage to units as follows:

  Dist from GZ    Unit Damage
   Rad   Diam   Min   Ave   Max
     0     1    100   200   300
     1     3     95   190   285
     2     5     90   180   270
     3     7     85   170   255
     4     9     80   160   240
     5    11     75   150   225
     6    13     70   140   210
     7    15     65   130   195
     8    17     60   120   180
     9    19     55   110   165
    10    21     50   100   150
    11    23     45    90   135

Based on testing by Zombie.

So, the Blaster Bomb is rated at 200 HE damage, and does that - but on average at ground zero. Then the range decreases by 10 per tile away from GZ. Maximum damage decreases by 15 (3/2*average), and minimum damage by 5 (average/2).

Unlike damage to units, tile (i.e., terrain) damage is fixed, and is equal to the minimum damage at that radius (i.e., half the average).

Most large explosions are "nipped" as shown above; in theory the Blaster could've kept going for eight more tiles until it decreased to zero. (But the blast pattern would've been HUGE!, Diameter=39.) Some smaller explosions are not nipped, and decrease until they drop off to zero.

Blaster Bomb Pattern

A screencap showing Blaster damage. Just for the halibut.

Typical blaster bomb damage pattern

Ground Zero Effect

Ground Zero Effect due to explosions

Units at ground zero (center of blast) and the eight adjacent tiles (GZ+1; nine tiles in total) receive damage through their Under Armor. All others receive damage to the side facing ground zero (never Under Armor).

This is true regardless of whether using thrown items (grenades, Hi-Ex) or shot/launched explosives (AC-HE, HC-HE, Rockets, Blaster).

Susceptibility

Critters have the following susceptibility or resistance modifiers to explosive damage:

  Silacoid    130%
  Sectopod     80%
  Zombie       80%
  Tanks        70%
  Cyberdisc    60%

So Silacoids are more susceptible, presumably because they are close to the ground.

Explosive Map Objects

There are several map objects that will explode when destroyed:

ObjectDescriptionArmourHE DamageImageLocation
U_PODS[00]UFO Fuel Pod #12060U PODS 00.gifTerror Ships, Battleships, and Alien Bases
U_PODS[01]UFO Fuel Pod #23070U PODS-02-.gifTerror Ships, Battleships, and Alien Bases
U_PODS[02]UFO Pod2045U PODS 04.gifTerror Ships, Battleships, and Alien Bases
U_WALL02[51-54]UFO Navigation*1540U WALL02-51-54-.gifAlien Bases and all UFOs except Scouts
URBAN[85]Fuel Bowser1846URBAN-85-.gifTerror Missions (Service Station)
XBASE[25]Fuel Drum1260XBASE2-25-.gifX-COM Base (Hangar)
XBASE[32]Missile Warhead1040XBASE2 32.gifX-COM Base (Missile Defenses)

While many terrain objects can burn (such as vegetation and many human structures), these are the only ones that actually explode. However, it must be noted that even though these objects do explode when hit, the damage they produce is not High-Explosive. It is Smoke. Thus, they function as a Smoke Grenade at best. Some players have reported that these objects do produce damage to health on aliens and civilians, but it has not been fully substantiated yet.

Object Destruction

EqTb-00.gif

Only explosions (not shot weapons) can destroy dropped equipment and other objects on the ground. They are destroyed by blast strengths greater than the values in this table. Unit names refer to bodies, both stunned and dead:

>HE  Destroys
  8  Electroflares
 12  Standard pistol clip and civilian males(?!)
 20  EVERYTHING else not otherwise mentioned. Includes ALL ammo, ALL large bodies
     (both XCOM tanks and large aliens), unarmored soldiers, even Elerium.
 26  All regular (small) sized aliens' bodies
 30  Soldiers in Personal Armor
 40  Soldiers in Power or Flying Suit, and Blaster Launcher
 45  Plasma Pistol
 50  Plasma Rifle and Heavy Plasma              - Values provided by Danial from OBDATA.DAT[42]

Blast magnitude is stated as the average blast damage for a tile and it must be greater than the value shown. Explosion damage for objects is fixed at the average - it does not vary as with explosive damage to units. You will always see the same things destroyed by a given average blast level. This makes it similar to terrain damage, but object destruction differs in that 1) it works off the average damage, and 2) HE must be greater than the value shown. (Tiles are destroyed when HE is equal to average/2.)

Object Destruction Example: A regular grenade is HE 50. Its average strength drops off by 10 per tile out to five tiles. Counting ground zero as the first tile, here are blast strengths and what's left after a grenade blast (sort of a reverse of the above):

 Radius HE  SURVIVES
    1   50  Plasma rifle and heavy plasma (HE must be greater than 50 to destroy these)
    2   40  PS/FS Soldiers, the three plasma weapons, Blaster Launcher
    3   30  Same as 40 except Personal Armor soldiers, too
    4   20  Everything except flares, pistol ammo, and male civs
    5   10  Everything except flares

By playing with explosives and distances from a blast, you can select how much blast damage is given. Example: A grenade (HE 50) can't touch Heavy Plasma, but HC-HE (52) can destroy everything. At its edge four tiles away (inc. GZ), the HC-HE is strength 22 and leaves alien bodies and other things tougher than 20 HE. Et cetera.

Despite this table, note that aliens use very strong explosives. The alien grenade (HE 90) is 30 average HE at its edge; the Blaster (200) is 90 at its edge. See "HE At Edge" in the table above.

Ammo loaded in a weapon plays no part in the damage check and cannot be destroyed, even if the host item is vaporised. It remains defined as being inside (regardless as to whether that item actually exists or not), and will be recovered at end of combat as per the normal rules. If a weapon is toasted and a new item takes it's place in the table the clip "pops back into existence" inside that.

An easy way to see this effect in action is to have a sectoid prime a grenade then drop all it's gear. Once the dust has settled you'll find the gun gone and the clip shoved somewhere it really shouldn't go, adding insult to injury.

Items made from alien alloys (including FS/PS) are usually (but not always) more robust.

Stunned aliens destroyed by explosions do not count toward kill Experience or victory points (Score at mission end), nor do they affect enemy Morale. They just disappear. Same goes for your stunned troopers killed by blasts; they do not detract from score or affect morale. But they are dead and gone!

Blast Diameters

Blast diameters differ according to terrain type. The table below was copied from a post by Zombie. To get radius, subtract 1 and divide by 2:

                                  Grass, 
                                   Lawn,  
                                   Corn  Dirt, Asphalt              Polar
                                  Fields,Weeds, Roads, White         Snow,
                            Wheat Desert White   Tin   Tile Concrete Mars  Mtn. Alien
Cost    $/HE   Weapon   HE Fields  Sand  Shngls Roofs  Roofs Walkway Sand Tundra Floors
 700    15.9  AC - HE   44    7     7      5      3      1      1      0     0     0
 300     6.0  Grenade   50    7     9      7      5      3      3      1     0     0
 500     9.6  HC - HE   52    7     7      7      5      3      3      1     0     0
 500     7.1   Prox G   70   11    13     11      9      7      7      5     0     0
 600     8.0  Small R   75    9     9      9      9      7      7      5     0     0
6700+2E 74.4  Alien G   90   13    13     13     13     11     11      9     3     0
 900     9.0  Large R  100   13    13     13     13     13     13     11     5     1
1500    13.6   Hi Ex.  110   13    13     13     13     13     13     13     7     3
8000+3E 40.0  Blaster  200   23    23     23     25     25     23     23    23    21
 Tile Armor -     Initial     6*   5?     10     20     10?    20   25-40   40    50
See next section     Dead    50   255    255    255     30?   255  30-255   20    50

* "Wheat" is complex - see Note 3 under Tile Characteristics

Where HE is the High Exposive rating for each round and: "White Shingles" is the roof on the gas station complex, "Mars Sand" is the soil on the Martian surface in Cydonia, "Alien Floors" is the floor of an alien base (alien ships were not checked), and "Concrete Walkway" is sidewalks near buildings or roads. Buy price or manufacturing cost are also shown (part cost only; does not include labor), whether Elerium-115 is needed ("+E"), and "Dollars per HE" (Cost/HE).

Note that these diameters only show damage to terrain. Damage to units is still done out to the radius for each bomb, as shown in HE Statistics above. So you can still be killed by a Blaster if 11 tiles away in a UFO, even though the hard UFO floors are only damaged out to 4 tiles from GZ. The tiles do not "soak up" any damage AFAIK. (Not counting tiles with HE Block, such as walls.)

For an Excel spreadsheet with 2D diagrams of all blast patterns (including stun bomb and tanks), see this.

Terrain tile properties (Armor, HE Block, etc.) can be readily seen in DaiShiva's excellent MapView program.

Distance from Ground Zero

"Distance" from GZ for explosives is actually computed by taking the TUs needed to walk to tiles in the blast radius. For example, 2 diagonal tiles away is considered to be 3 tiles since it takes 6+6=12 TUs to walk (and 12/4=3). This can be modelled on a spreadsheet using the equation:

Distance = INT( MAX(X,Y) + MIN(X,Y)/2 )

where X and Y are positive offsets from Ground Zero

This simplified approach sometimes makes blasts a little stronger down diagonals than would be expected from the Pythagorean theorem (a2=b2+c2; a=SQRT(a2+b2)). Using Pythagoras, a diagonal tile is 1.4 tiles away, but the game considers them 1 tile away (INT(SQRT(2)). The 1.4 would've led to 1/1.4=71% blast strength. This is the worst case; the TUs approach is much closer to Pythagoras on a percentage basis at greater diagonal distances.

HE Block

Some tiles have a property called "HE Block" (High Explosive block, a.k.a. HEB) which causes them to dampen an explosive blast proceeding past them. This is basically what makes a wall, a wall... without this property set, explosions would proceed through walls and other objects as if they didn't exist.

For the record, tile armor values (see below) do not dampen explosions in any way whatsoever. Tile armor only affects whether that tile is destroyed by an explosion; blasts otherwise proceed entirely unhampered. Only HE Block dampens explosions. If you set outer UFO hull armor to 255 (the highest it can be) and its HE Block to 0, a blaster explosion on the hull will be the full, entirely "round" 23 tiles in diameter, imparting damage to anything caught in its circle as if the hull did not exist. (But the hull will be unaffected, because its armor is >100.)

Also, HE Block only dampens explosions "past" the tile in question. It does not dampen the blast for that tile, itself. Thus, an outer UFO wall takes the full force of a blaster bomb (200/2=100, just enough to take out one wall tile), but it's HE Block 100 stops any of the blast from proceeding past the wall "inwardly".

Playing with HE Block shows that explosions proceed from ground zero outward in a way that only directly impacts the four tiles that are directly adjacent (due north, south, east, and west). Blast damage never proceeds in a diagonal fashion per se; instead, diagonals are filled in as a function of damage going sideways from these four main "rays". As Bomb Bloke has observed, one can trace HEB back to its "source" by looking for the places where there were decreases. In other words, you are either seeing main rays decreasing by 5, or 50% moving laterally (then outward), and can trace HEB back to its source by comparing a blast with HEB, to one without it... where was the usual progression dampened?

XCOM map tiles can have up to four types of terrain: a ground tile, a north wall, a west wall, and a terrain object (such as a tree or furniture). This is not counting "mobile" items such as units or equipment dropped on the ground.

HE Block assigned to ground tiles is ignored by the game. Thus e.g. the HEB 25 of hay loft ground tiles is just a data entry error(?) that doesn't affect anything (see Tile Characteristics).

A wall is a separator between the two tiles that it is drawn between. This is not quite true for objects, however.

In terms of HE Block, this is best demonstrated by directly impacting e.g. a blaster on the object, coming at it from the side: a lone object in the middle of a field will show a blast pattern exactly equal to simply having set off the bomb in the middle of the field, with no object there - the HE Block of an object is ignored when a blast impacts the object itself. Conversely, if a wall is hit on its face, it will HE Block damage from being passed on to the "other side" of the wall.

But this only applies to objects that are directly hit. If, instead, we exploded a blaster against the ground right next to an object or wall, the blast pattern is very similar for them both - because now the object is intercepting one of the "rays" from the explosion, instead of exploding "itself". In other words, the blast front has directionality relative to the object, and is blocked in a "logical" way, if ground zero is to the "side" of it.

All items in a tile (ground, walls, and terrain object) receive the same force of explosion. As described above, this is the current blast strength at that tile, which equals the average blast strength divided by two.

For the record: Soldiers do not have any HE Block. If you group a lot of them together and then explode something near them, there is no difference in the explosion pattern or strength where they stand.

Anyone interested in testing HE Block, be sure to see Bomb Bloke's fantastic numerical tileset which makes blast testing far easier than it would have been. Find his hacked terrain here, or bundled with a savegame here. To see a screencap of the tiles in action (and a good example of what I'm discussing!) see this message. --MikeTheRed

When Is a Wall not a Wall

"Blow through" on a North wall due to a Blaster Bomb explosion outside the UFO.
These are the only "true" north and west outer walls on the third floor of the battleship, as seen in MapView. All other outer walls are subject to blast through, although diagonals (not parallel to due north/south/east/west) may show funny patterns, or zero blast through. Also note all inner walls ARE true walls.
An un-entered large scout that has received external shelling from rockets. Although not enough to damage the craft itself, the "punch through" blasts have been able to kill crew members in some cases.

Some outer UFO walls are not true "walls", and a Blaster hit propagates through them at 100 HE.

Each map tile in UFO consists of four elements:

  • Ground
Dirt, grass, cement, etc.
  • Object
Trees, lamp posts, UFO power sources, etc.
  • North Wall
Fences, hedges, doors, etc. (placed along the northern edge of a map tile).
  • West Wall
Fences, hedges, doors, etc. (placed along the western edge of map tile).

At any map location in the battlescape, up to one of each of these four tile types can exist.

To demonstrate a standard example, say a Blaster Bomb hits a door with 100 HE Block. Any alien unlucky enough to be on the outside would be killed instantly, however anyone on the far (inner) side of the door would escape all damage. This is because the door is a "true" (north) wall and stops the blast from moving inward (even if it is itself destroyed).

On the other hand, what if such a shot were directed at a tree (14 HE block)? Well, so long as the missile hits it DIRECTLY, the tree (which is an "object", not a "wall") won't block the explosion at all - It'll only provide cover if the blast is side on (i.e., not centered on it).

Ordinarily the distinctions don't matter much. But there's at least one place where they might - As pointed out by Danial, some outer UFO "walls" hit by Blasters have damage penetration past the wall, even though they "shouldn't" (see first image). What's happening is that some outer walls are actually "objects", same as the aforementioned tree - when they are hit directly, the explosion propagates outwardly from the object as if it did not exist (though the walls to the sides do prevent the blast from spreading in anything other than a straight line). This is very different from a "true" wall, which shows proper directionality.

See the second battleship graphic, which shows the only true north and west outer walls on the third floor of a battleship. (The north and west walls of the individual tiles - which are being used to make the south and east walls of the battleship.) All other outer "walls" are subject to blast through, as seen in the first picture. That said, however, HE Block has not been well tested/understood in regard to diagonals.

Tile Characteristics

This section is mainly for folks doing research on explosion propagation. Values were gathered with DaiShiva's excellent MapView program. Caution: You must install the extensive MicroSoft .NET platform to use MapView; see DaiShiva's site. For more tile armor values, see Destroying Terrain. That page does not include HEB and Dead tile info, however.

 Ini Ded HEB Type                                                          _
  80  50     Most UFO floors                            UFOs AND ALIEN BASES
 100 NDT     UFO roof
 100 220 100 Outer UFO walls
  80  50  80 Most inner UFO and base walls. Dead tile does not have HEB.
 100  50 100 Inner UFO "security" walls and doors (See Note 1)
 100  70  80 Base wall "windows" (almost indestructible, but propagate blasts)
             Two on lower command center; also at checkpoints (UBASE_06)
  60 100  60 Most parts of 4-tile vats in bases and UFOs, except...
 200 100 200 "Back" (NW) corner of green 4-tile vat invulnerable! (UBASE_02)
  80  50  80 Most inner UFO doors
 100 NDT     Partial UFO floors and adjacent tiles along diagonals etc.
  50  70  30 Power Source (Dead tile stronger than original, and also has 30 HEB)
  50  50     Common gray base floors
 150  50     Green start tiles
 200  50     Red elevator tiles. Yellow rays add 200 armor.
  50  65     Purple flooring in UFOs and command center (come up through it!)
  60  60  60 Flashing orange and aqua walls (good backdoors sometimes!)
  70  50  70 Green-on-black comp display wall (trapdoor to BB control room)
  90 100     Dark black base floor in gardens and around command center    _
  25 255     Arctic ground                                            ARCTIC
  20 255     Road                                                     CITIES
   8 255     Smooth grass
  10 255     Grass patches and dirt
  15  30     Gas station ceiling - 150 Flame
  10  30     Gray store floor
  15  30     Slate roof for buildings - 160 Flame
  18  50     Gray warehouse floor - 155 Flame
  15  30     Rough gray concrete store roof - 150 Flame
  12  40     Pastel pink(?) indoor tile - 111 Flame
   8 255     Flowers
   6  50     Pink patterned carpet - Normal 20 Flame, DT 100 Flame         _
  40  30     Sand. Crater objects add armor, HE Block, 4 TUs.        CYDONIA
 100 NDT     Green Start tiles. All others as for alien bases.             _
   5  25     Sand                                                     DESERT
   5 255     Grass                                                      FARM
  10 255     Dirt and cultivated fields
   6  25     Wood floor - Flame 16
   6  25  25 Hay loft ground floor - Normal 12 Flame, DT 25 Flame
  10 255     Stable - Flame 10
  30  35     Cobblestone floor - 160 Flame                                 _
  10  30     Light green weeds add 8 armor, 25-30 Flame               FOREST
   8  30     Plants add armor and HEB; see Note 2                     JUNGLE
  40 NDT     Normal ground. Also see Mountain Madness.              MOUNTAIN
  50 NDT  50 Solid mountain walls (full height)                            _
  15  80     Common pink(?) or gray floors, inc. Access Lift       XCOM BASE
  10  80     Lighter tile in center of some common floors
  12  70     Blue floors
  16  80     Hangar floor                                                  _
 255 NDT   0 Ramp object. See Note 4.                             XCOM CRAFT
 255 NDT   0 Floor of craft

"Ini" is initial tile armor; "Ded" is tile armor for the next ("dead") tile that appears after the initial one is blown away. If no tile is indicated (DeathTile=0), NDT is put. This means that raw earth will appear when the tile is killed, on ground level (or nothing does if above that, such as with UFO roof). Nothing is strong enough to break through Death Tiles with armor 255. Thus you can't break through artic ice to reveal raw earth, which makes sense. Basically anything over 100 (half the blaster's damage) cannot be broken through; thus elevators and start tiles (except in Cydonia surface!) are safe from explosions.

Note 1: The inner UFO walls with "crown molding" have higher armor, and can be considered "security walls". The whole third level of battleship is this, and it's also found around the control room in large UFOs. Also, the darker doors without the line down their center are also higher strength. These are also generally found in secure areas; the top of the battleship elevator is ringed by them. These strong doors are also found in a few interesting places such as the entrance to the "engine room" on the bottom floor of the Supply Ship (even though the walls there are not security walls).

Most solid floors etc. have no flame ("Flammable") value. Most plants and human buildings do. Some tiles look weird, but make sense when you think about it. For example, cobblestone in farms has a high flame value - but it's found as the first floor of wooden buildings. Also (Note 2:) Most largish plants (shrubs and larger) had HE Block values. The jungle, in particular, has many full trees with HE Block of 20. Don't ask me why the hay loft ground floor has HEB=25.

There are a number of small objects that add armor to a tile. Example: Rocks in the desert are separate objects, with 20 armor. But snakes and bones are just painted onto a common desert tile; they are not separate objects nor do they add anything to the tile properties. Generally, anything that adds TUs also adds armor and possibly HE Block and Flammability. Most objects (including walls) that block movement add armor and HE Block, as well.

Note 3 (from Blast Diameters): For what it's worth, the effects of e.g. wheat and flowers in the farm map are actually added to the base tile (and add TUs to it). They are separate objects in addition to the ground tile. The additional TU costs can be seen in MapView, such as 2 (i.e., +2) for wheat. They also have their own armor ratings. Thus the wheat itself has Initial Armor 6, DT Armor 50 (this one shows burnt crops), which then goes to another DT (dirt) of Armor 255. But the tile it's on has Initial Armor 10, then goes directly to the same final DT as wheat (Armor 255). What happens is that wheat tiles go directly to their DT if blast strength is 60+, or to burnt crops if 60 > strength >= 6.

Note 4: All ramp-section objects add 4 TUs to underlying terrain except the middle and top of Avenger's ramp only adds 2 TUs. I think Danial has pointed this out before. Also see Mountain Madness.

Take these values as a rough guide. Some were hard to tell apart. If you want to do research on a particular tile, please double-check MapView before spending a lot of time on it! - MTR

A larger list of terrain objects and their armor values can be found at Destroying Terrain.

Experience Points

Experience that may be gained with explosives is as follows.

Any alien (not under mind control) caught in a blast radius will give experience points toward Firing Accuracy. So one blast can give many Firing experience points (XPs). It does not matter if the alien was not harmed (i.e., damage was blocked by armor); you still get experience points if they were in the blast radius. Mind controlled aliens are considered friendly and do not give experience points.

Note that if no one actually throws a thrown explosive (it's merely dropped), your first soldier gets the Firing Accuracy experience (even if a tank or if dead!). Thrown objects are attributed to the last person to throw them, or default to your first soldier "slot" if no one threw it. Your tanks always occupy the first slot(s) (but enemy tanks such as the cyberdisc do not occupy your first slot). Keep this attribution in mind when using the Grenade Relay, if you're trying to pass Firing experience around. As it were.

The Small Launcher's "explosive" stun bomb also gives Firing experience. Again, even if aliens did not actually fall unconscious (or receive any stun at all). Stun bomb radius in desert terrain is 5, diameter 11.

If thrown, one Throwing Accuracy experience point will be given. This holds true for throwing anything, explosive or not.

If you make a reaction shot with a projectile explosive, you will receive one Reactions experience point, even if many aliens were hit by the blast (giving you many Firing XPs). Technically, you were only reacting to the movement of one of the aliens.

To see how experience points translate into skill points (when combat ends), see here.

NOTE: The Proximity Grenade does NOT give Firing experience to the thrower. Instead, it gives Firing experience to the person that triggers it to explode. Keep this in mind because this tends to make it a poor choice, especially early in the game (SIGH!).

Unusual Explosives

UFO Power Sources

Typical PS explosion using Bomb Bloke and Zombie's setup
The parameters for UFO Power Sources (PSs) have been worked out, as seen here. PSs explode with a radius 11 (diameter 23) explosion of average strength 215 (stronger than a Blaster!). However, what's not discussed there is that this explosion breaks the mold of how explosions usually work, for two reasons:
  1. PSs explode with a variable blast strength versus terrain. Standard explosions impart precisely 50% of their average (rated) strength versus terrain; they are not variable, versus terrain (but are versus units). Still, while a PS's HE strength varies versus terrain at GZ, this GZ strength does otherwise drop off by a fixed 5 strength for each tile away from GZ, just like standard explosions. (The inset shows a PS explosion in a game using Bomb Bloke's super-cool terrain plus Zombie's sweet PS testing scenario.)
  2. PS explosions impart 215 ±35 HE damage (107.5 ±17.5 versus terrain). 35 is 16.23% of 215. We've seen Damage ranges of ±25%, ±50%, and ±100%. But ±16.23%?? Further analysis of the game code yielded the actual equation used: 180+(Rnd#×70). This more accurately describes how the blast is calculated.
  3. PS explosion seems to have weird results vs Units, based results from reloading a recovery mission on a crashed Medium Scout with Mutons on Superhuman.

All in all, PS explosions are in a league of their own. It looks like the developers hand-coded some of the parameters, but otherwise used a lot of the explosion routines.

Stun Bombs

The overall details on the Small Launcher's "explosion" are shown on it's page. But what's not shown is that has its own set of rules versus standard explosives. In a nutshell, while the stun "blast" follows all normal rules of a propagating explosion, it inflicts stun Damage on units as if it were a weapon.

Typically, HE explosions do damage to units equal to 50%-150% of the explosion strength. But the stun bomb imparts 0-200% of its stun "explosion" strength to units, even though its damage drops off by 10 per tile, as with other explosions. Thus it uses a hybrid of explosion and firearm damage mechanics.

This leads to an "odd" scenario like this, as seen in limited testing:

  • If a stun bomb is hacked to strength 250 stun and shot at a wall with HE Block of 120, no units behind it receive any stun. This follows the usual explosion rules of: Half strength is applied to terrain at ground zero (GZ), which falls off by 5 per tile away from GZ; thus the stun bomb is 125 vs. terrain at GZ and 120 at GZ+1. Soldiers get no stun because the 120 HE Block nullified all the explosion strength. (Wall armor was set to 0 - tile armor never impedes explosions; only HEB does.) Ok, no problem here.
  • But if the 250 stun bomb is shot at a wall with 110 HEB, a unit right on the far side was seen to get 33 damage. How did that work?
    • The stun bomb is 125 vs. terrain at GZ
    • At GZ+1, it is 120, minus the 110 HEB, leaves 10 for damage to terrain
    • But damage to terrain is 50% of the average explosion damage. And the stun bomb can do up to 200% damage to units. If 10 is 50%, then 40 is 200%. Thus, it "makes sense" that a unit was hit for 33. In its own weird way.

It seems that the force of the explosion checks its strength versus terrain as it progresses, and, if it has not become zero, then it back-calculates average/rated damage - and inflicts the stun damage. See, if the game were tracking average/rated damage as a blast front progressed, when the stun bomb hit the wall, it would've become 250-10=240 for the next tile, minus 120 equals 120 average/rated damage on the next tile where the unit was - but wait, no. See? That can't be right, because this would have inflicted 0-240 stun damage on units, from the average of 120 carried forward. But high values were not seen (in very limited testing!). Also, of course, the unit did not receive exactly 5 stun damage, as would have been expected if the stun bomb explosion exactly followed the rules of explosions. So this hybrid event (explosive progression but unit damage) has given us insight into how XCOM tracks the damage that an explosion front will incur - it carries terrain damage (50% of rated) forward, then back calculates rated damage, if a unit is there.

Playing With Fire

Hacking HE versus Blast Diameters

Hacking HE (OBDATA.DAT[22]) shows that explosion patterns fall into 2 or 3 categories:

  • All projectile explosives (AC, HC, S & L Rocket, and probably Rocket Tank) have "constrained" patterns that are always smaller than expected - their blasts never "die away to nothing" at their edge. They also continue to have an ever-increasing outline (larger diameter) for as high as HE can be hacked.
  • All grenades (standard, alien, prox, Hi-Ex) have "natural" blast patterns that do "die away to nothing" at their edge - up to HE 61. At 62, it takes on a fixed pattern which shows some "constraint" in the sense of not being what would naturally be expected. At this point it is radius 6, diameter 13. And then their pattern never changes (i.e. enlarges) past what is seen at 62, even if you increase HE all the way up to 255. Even much higher than HE 62, grenades' pattern is still only radius 6.
  • Guided weapons (blaster and presumably fusion tank) follow the same pattern as grenades but their blast pattern continues to grow in size, until one reaches 112 (radius 11, diameter 23). At this point it too becomes fixed, no matter how much higher HE is hacked.

Thus blast radii and diameters can be described with these equations:

           Type                   Radius         Diameter         Pattern Limit Reached At
   Projectile Explosives       INT(HE/20)+1    2*INT(HE/20)+3    HE 240 (r=13, d=27)
Grenades and Guided Weapons   INT((HE-2)/10)  INT((HE-2)/5)+1    Grenades: HE  62 (r= 6, d=13)
                                                                 Guided:   HE 112 (r=11, d=23)

For the above, only the blast pattern a.k.a. "outline" is being talked about. Within the blast pattern, all explosives follow the expected, simple rules of: Average HE at ground zero, decreasing by 10 per tile outward (for damage to units; by 5 for damage to terrain), and all points (and explosive strength there) can be described in terms of distance from GZ using the "walking TUs" method.

These properties of hacked explosive strength lead to the following observations:

  • Since there is only one (unhacked) grenade or guided weapon with an HE rating less than the point of its "radius of constraint", only the humble grenade shows a quite round, "natural" blast pattern outline. It's the only explosive that truly decreases to 0 all around its edge (although the prox mine comes very close).
  • On the flip side of that, as HE gets larger and larger (with or without hacking), the edge of blast patterns becomes more and more lethal. It's easy to see that this would happen with grenades and guided weapons - their diameter no longer increases, even when increasing their explosive power. But hacked projectiles are also dangerous at their edge - even though it is not constrained, per se - because their radii only increase by one every 20 HE, even though damage only decreases by 10 per tile. Thus, they increase by 10 at their edge (+20, -10) each time their radius increases.
  • Here are some examples of maximally-hacked blast edges, versus the worst seen in an unhacked game:
    • A grenade hacked to HE 255 has an average of 195 HE at its edge (r=6, d=13)
    • A guided weapon at HE 255 has an average of 145 HE at its edge (r=11, d=23)
    • A projectile explosive at HE 255 has an average of 125 HE at its edge (r=13, d=27)
    • Compare how the most dangerous unhacked example is a blaster (HE 200), which is 90 average HE at its edge (r=11, d=23)...
    • But the second-worst case is Hi-Ex (HE 110), which is 50 at its edge, because it is a grenade constrained to just r=6, d=13. (Not the Fusion Tank at HE 140, because guided missiles can be up to r=11.)
  • Many blast patterns have the same r=6 outline in an unhacked game. This is because all but one grenade is constrained to this, plus one of the projectile patterns (for Large Rocket, HE 100) happens to precisely coincide with this, as well (as it would for any projectile with HE 100-119).
  • If a stun bomb (stun strength 90) is hacked to be an explosive (OBDATA[31]=2), it too follows the pattern for projectile explosives. This includes if its HE is also then hacked.

Presumably, the pattern type is determined by whether something has the OBDATA grenade type set, or it is ammo, or it is guided.

Examples of the patterns (both real and hacked) and the walking TUs map can be found in an Excel file here.


Hacking HE versus Explosion Sounds

When HE is hacked, there are two types of sound heard:

  • The small "whoomf" up to HE 80, and
  • The big bone-jarring explosion heard at HE 81+.

Another thing is seen:

In addition to the projectile-launch sound each type of projectile weapon makes, the Auto-Cannon and Heavy Cannon also do a slightly odd thing: if hacked to HE from 74 to 80, they make the "whoomf" sound twice when they explode.

Hacking HE versus Walls

The Blaster Bomb is the only thing capable of blasting through a UFO outer hull (walls and roof). It does exactly 200 damage at the epicenter and only ever knocks out one tile.

When we boost the power of the humble High Explosive with a game editor we see the following:

  • 190 for HE strength is not enough to bust a hull open.
  • 200 is, but only one tile wide.
  • 210 opens up a hole 3 tiles wide
  • 220 opens up a hole 5 tiles wide.

For every 10 points of HE strength above 200, it adds 2 to the width of the hole.

- reposted from NKF/Jasonred/Zombie discussion, strategycore forums 2005 -JellyfishGreen

Mile-High Madness

Mountains have the inherent weirdness that they "weaken" some structures, as pointed out by NKF, Bomb Bloke, and others. For example, a Blaster explosion on the ground below an XCOM craft will destroy its ramp and landing struts, in mountain terrain. Ordinarily, these objects are indestructible (armor=255) for all three troop transports. You can even take them or outer UFO walls out with an alien grenade (except for "true" North and West walls (see above) - anything that's enough to destroy tile armor 40 (HE 80+).

The reason for this unusual behavior is seen by using MapView. It seems that XCOM programmers accidentally pointed to an object instead of a tile for the death tile of mountain terrain. It looks like they pointed to MCD id 76 (a stump object) when they should've pointed to MCD id 77 (scorched mountain ground tile). Perhaps someone stuck in an extra tile without keeping an eye on the pointers. In any event, this object only has armor of 20. It is theorized that when mountain terrain is destroyed (armor=40), the stump object then erroneously replaces e.g. the craft ramp, and then the explosion is also enough to take out that object. Note that the code for explosions appears to process ground first and then process objects; this must be how the inadvertent stump object also gets destroyed. (Otherwise it should've been seen all along the outer edge of a blaster explosion, where the blaster's tile-damage strength is less than 60; see Blast Propagation.)

Conversely, if you shoot a weapon at mountain ground terrain, you will see the stump. This is because shots against terrain only do damage to the element they hit, whereas explosions are checked against everything in a square (ground, two walls, and object, if any). You can even turn craft ramps and gear into stumps, if you try hard enough. Most shots will hit the ramp instead of ground, but eventually one will miss and burn the dirt, turning the ramp into a stump!

This strange behavior is also seen on flat mountaintops. All the common flat mountain ground tiles point to the wrong death MCD id.

A final oddity due to the incorrect tile is that mountain ground destroyed in an explosion will burn for three turns. Most common ground tiles have 0 Flammability and will not burn after a "regular" explosion. (They'll burn if hit by incendiaries, though.) This is because the stump object has Flammability=14 and is set to burn for 3 turns.

A fix for all of these problems can be found here.

See Also