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Battle_Cat_Cringer

Fire Chance

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Helena with 6% fire chance. 249 shots of HE fired. Should be about 15 fires. 3 fires only. I understand some have reduced fire chance, but 3 only?

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Having done many set on fire missions, I have come to the conclusion that you can't ever count on them. The first one seems to be easy, after that you can't seem to get one until the Damage Control Party cool down has ended.

Edited by Sovereigndawg
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https://wiki.wargaming.net/en/Ship:Fire#Fire_Chance

 

Fire chance is a shell property. Chance of fire is the result of an equation. Ships have build in resistances depending on tier and upgraders they can take that reduce the chance of a fire. Additionally, shells that hit an area already on fire, or hitting a ship that has DCP active will obviously not start a fire either

Edited by _BBaby
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Have a read of the wiki: https://wiki.wargaming.net/en/Ship:Fire

Essentially all ships have a "base fire coefficient" which reduces the chance of fire. It's based upon your tier and whether you have a stock or upgraded hull.

 

Quote

Fire Chance

Fire Chance (the chance a shell or bomb will set a fire) is calculated by combining a base chance for the ordnance to set a fire, the target ship's intrinsic resistance to fire, and certain modifiers, as shown below.

Fire Resistance

Each ship hull has an intrinsic resistance to fire. The amount of resistance is based on ship type, ship tier, and the hull that is currently equipped (Stock or Top). (Premium ships all have the Top Hull.) This resistance is expressed as the Fire Resistance Coefficient (FRC). The lower the coefficient, the more resistant the ship is to catching fire.

180px-Fire_UI.png
magnify-clip.png
The user interface will display several different indicators to let captains know their ship is on fire. The timer shows only the duration of the most recent fire set.

The Fire Resistance Coefficients (FRC) are shown below:

Ship Tier WowsshipclassDestroyerDefault.png WowsshipclassCruiserDefault.pngWowsshipclassBattleshipDefault.png (Stock Hull) WowsshipclassDestroyerDefault.png WowsshipclassCruiserDefault.pngWowsshipclassBattleshipDefault.png (Top Hull) WowsshipclassAirCarrierDefault.png (all)
Tier I 1.0000 N/A
Tier II
Tier III 1.0000 0.9667
Tier IV 0.9334 0.9001 0.8002
Tier V 0.8668 0.8335
Tier VI 0.8002 0.7669
Tier VII 0.7336 0.7003
Tier VIII 0.6670 0.6337
Tier IX 0.6004 0.5671
Tier X 0.5338 0.5005

Base Fire Chance

"Projectile Base Fire Chance" for artillery is displayed in the Port screen by mousing over the Main Battery or Secondary Armament entries in the Artillery section. Only HE shells have a Fire Chance. In addition, each ship entry in this wiki includes the fire chances for main and secondary HE shells.

For aircraft bombs and rockets, the base fire chance is a characteristic of the size and type of ordnance used and varies between 4% for small rockets carried by attack squadrons and 64% for large HE bombs. See the tables in the Aircraft article for more info. The information can also be view in the Port screen by mousing over the appropriate type of squadron in the Aircraft section.

The Calculation

The chance to set fire for a single high explosive shell hitting a ship is calculated by the following formula (the formulas for airborne rockets and bombs are similar):

 

Fire Chance = FRC · ( 1 - DCM1 ) · ( 1 - FP ) · ( ( FCB · IFHE ) + PY + Σ S )

where:

  • FRC — the ship's Fire Resistance Coefficient (see above).
  • DCM1 — the effect of the Damage Control System Modification 1 upgrade: 5% (0.05) with the upgrade installed, zero without.
  • FP — the effect of the Fire Prevention skill: 10% (0.10) with the skill, zero without.
  • FCB — the Projectile Base Fire Chance (see above).
  • IFHE — the effect of the IFHE commander skill: 50% (0.5) or one without the skill.
  • PY — the effect of the Pyrotechnician commander skill: 0.01 with the skill, zero without.
  • Σ S — the sum of the effects of the mounted Signals Victor Lima +1% chance of causing a fire for bombs and shells with a caliber above 160mm / +0.5% chance of causing a fire for bombs and shells with a caliber below 160mm. / +4% chance of causing flooding. and India X-Ray +1% chance of causing a fire for bombs and shells with a caliber above 160mm. / +0.5% chance of causing a fire for bombs and shells with a caliber below 160mm. / +5% to the risk of your ship's magazine detonating.: +0.01 or +0.005 each depending on gun caliber, else zero.

As an example, we can compare the chance of a single Benson high explosive shell lighting a fire on an enemy Bismarck.

  • The Tier VIII Bismarck is using Hull B (Top) (FRC of 0.6337) and Damage Control System Modification 1; his commander is not skilled at Fire Prevention.
  • Benson fires 127mm HE Mk. 32 with a 5.5% base fire chance. Her commander is a Pyrotechnician (not IFHE) and is flying both the Victor Lima and India X-Ray signals.

The fire chance (per hit) would be:

(0.6337) x (1 - 0.05) x (1 - 0.00) x ((0.055 * 1) + 0.01 + 0.01) = 4.52% fire chance

If the Bismarck commander acquires the Fire Prevention skill, the chance would then be:

(0.6337) x (1 - 0.05) x (1 - 0.10) x ((0.055 * 1) + 0.01 + 0.01) = 4.06% fire chance

If the Benson commander didn't have Pyrotechnician or the signals equipped, the chance would be:

(0.6337) x (1 - 0.05) x (1 - 0.10) x ((0.055 * 1) + 0.0 + 0.0) = 2.98% fire chance

The above example can be used to demonstrate the usefulness of the Pyrotechnician skill on certain ships, especially those with a high rate of fire and a low individual fire chance per shell (such as Atlanta, Gearing, or Akizuki).

 

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Aside from all the things said above that are obviously on the mechanics side of things, just because a fire chance is 6%, doesn't mean there's a guaranteed number of fires. The dice is rolled for each time a shell hits whether it will set a fire.

I had battles with ships like Friesland, with ~500 shell hits and 5-6 fires. Some other battles for the same number of hits 20+ fires. That's just how RnG do.

Edited by warheart1992

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1 hour ago, Battle_Cat_Cringer said:

Helena with 6% fire chance. 249 shots of HE fired. Should be about 15 fires. 3 fires only. I understand some have reduced fire chance, but 3 only?

  I say its a rng thing.  Yes, you could get fires but you can also not.  Enemy ship can have skills/modules to reduce fire chances.  What skills are you running?

  I would think lower tier would start much fire except for British BB. 

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2 hours ago, Battle_Cat_Cringer said:

Helena with 6% fire chance. 249 shots of HE fired. Should be about 15 fires. 3 fires only. I understand some have reduced fire chance, but 3 only?

Each shell has a 6% chance of starting a fire...which also means each shell has a 94% chance of not starting a fire.

Each shell also has a 0% chance of starting a fire if the section of the ship is already on fire (& if your single girl g your shells & you don't change your aim for another section of the ship after starting a fire your shells are likely going to hit the same area over & over) or if Damage Control consumable is active (which after setting a fire on a BB if it is used by the target & you keep shooting through the whole DC is a whole lot of your shots that are getting 0% fire chance instead of the 6%).

Plus targets have various fire mitigating tools that may be in effect reducing your 6% chance...on each shell fired at them...

& other targets may have more fire mitigation equipped.

Lots of variables...the 6% is just a base variable...although there is at least 1 skill that increases fire chance on some BB targets...if they're silly enough to take it anyway.

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3 hours ago, Battle_Cat_Cringer said:

Helena with 6% fire chance. 249 shots of HE fired. Should be about 15 fires. 3 fires only. I understand some have reduced fire chance, but 3 only?

Your 6% chance is actually somewhere between 2 and 4%, depending mainly on the tier of your targets.

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3 hours ago, Battle_Cat_Cringer said:

Helena with 6% fire chance. 249 shots of HE fired. Should be about 15 fires. 3 fires only. I understand some have reduced fire chance, but 3 only?

 Just shoot at me if you see you me in game your fire % will jump to 30% I'm always on fire .

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5 hours ago, SoothingWhaleSongEU said:

Have a read of the wiki: https://wiki.wargaming.net/en/Ship:Fire

Essentially all ships have a "base fire coefficient" which reduces the chance of fire. It's based upon your tier and whether you have a stock or upgraded hull.

Interesting. So when you're doing a Fire mission I wonder where the tier "sweep spot" would be? 

Taking a mostly random guess I bet T7 Helena would be a good choice since she can shoot a lot of shells per minute but will still be a low enough tier where her targets' base fire coefficient won't be too good.

Edited by BitCrushed

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you have to consider that a significant portion of those shells might have struck a part of a ship that was already on fire. In that case you can't set it on fire and thus those shells should not count. Further, active damage control on a ship would negate any fire chances.

 

 

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4 hours ago, HamAndCheez said:

Do high explosive shell shatters/non-pens, torp protection hits, and bounces have any chance at all to cause fires? 

Yes. Any shell that hits a target that does not have its DCP active in a location that is not already on fire has an equal chance of starting a fire, regardless of whether it actually deals damage or not.

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