Consensus on Calcing Fire

[Agnaa]

So according to @Armorchompy, the precedent for calcs involving creating fireballs, lighting areas on fire, and the like is to use the density of air to get the mass, and then do heat change for that.

But the calcs I've been doing for a few years have used the density of flame instead, which is only 30% as massive. I did this at the advice of a calc group member, and had these accepted, one by @Mr._Bambu, and one by @DMUA and @Kepekley23.

I personally think the latter's preferable, since when you're creating fire, you only need to heat up the mass of the fire in a certain volume, you could presumably skip out on heating the rest of the air, so this makes for a fine lowball. But Armor wants to use air since that's what was previously occupying the area.

Also we've had some a difference with the heat change assumed, Armor seems to go with 1177 degrees of change, and I was told to go with 1134. I think mine's from assuming a room temperature of 16 degrees, and using the midpoint of 1100-1200, said to be the range of heat of ordinary fire.

And we've had an even more minor difference with the heat capacity of air, Armor saying it's 1003.5 J/(kg * K) and this website I was told to use saying it's 1006 J/(kg * K).

It sounds like either way, some amount of calcs would need to be changed, up to about a 3.45x difference either way.

 

[Armorchompy]

i mean you don't really need consensus

you just need to like, research which is right i'm sure there's papers on the details of it

(i don't feel like doing that)

 

[Agnaa]

The worry's that I don't think any real world equivalent actually exists.

Heating up air to 1200 degrees doesn't create a fireball, it just creates hot air. The only realistic thing would be, like, creating a fuel source and hitting its ignition temperature, which would just omega-downgrade fire feats.

 

[Armorchompy]

Ah

meh then idk, if something goes on fire instantly by your interpretation you'd also be able to do the KE of the air being moved which IMO is slightly sus, but I don't have that strong of an opinion about it

 

[KatBoi69]

Am I allowed to post here? If someone gives me two example calcs (one for each side) I can probably give you a scientifically accurate answer.

 

[KLOL506]

Not really sure which one's the best to go with but I'm currently leaning on using actual fire density instead. But I'm not educated well enough on the matter so I'll ask @DontTalkDT as well for this. Ciao then.

 

[KatBoi69]

Not really sure which one's the best to go with but I'm currently leaning on using actual fire density instead. But I'm not educated well enough on the matter so I'll ask @DontTalkDT as well for this. Ciao then.

So is there a reason that vsbw has decided against using heat of combustion, and stoichiometry based on the calculated volume of oxygen in the feat, to get AP from something like this?

Edit: I just want to state that, relevant to the OP, doing the calc with the density of fire is essentially assuming that the air combusts before it is heated. That doesn't make sense.

 

[Agnaa]

So is there a reason that vsbw has decided against using heat of combustion, and stoichiometry based on the calculated volume of oxygen in the feat, to get AP from something like this?

Edit: I just want to state that, relevant to the OP, doing the calc with the density of fire is essentially assuming that the air combusts before it is heated. That doesn't make sense.

Wouldn't you still need a fuel to be matter-created for an analysis like this?

 

[KLOL506]

So is there a reason that vsbw has decided against using heat of combustion, and stoichiometry based on the calculated volume of oxygen in the feat, to get AP from something like this?

Edit: I just want to state that, relevant to the OP, doing the calc with the density of fire is essentially assuming that the air combusts before it is heated. That doesn't make sense.

Couldn't say, the standards may have been made years ago regarding which material's density to use, much longer than before I even joined the wiki.

 

[KatBoi69]

Wouldn't you still need a fuel to be matter-created for an analysis like this?

True, but you don't get visible combustion (or any combustion) without fuel. I'm not super in favor of arguing that the standard needs to be, "assume there's H2 in the air and do stoichiometry," but it's a thought.

As for this thread, if you're just calculating the feat as "energy needed to heat the air to the temperature initiating combustion," then you should use the density of regular air, as it isn't fire until you hit that heat, under the current method.

 

[Agnaa]

It's not currently calculated as "Energy needed to heat the air to the temperature initiating combustion", it's "Heat energy that a fire occupying that area would have".

It's like, they're adding enough energy to create a fire through unknown means without needing an external source of combustion. A high-end would be doing E=MC^2 for creating the fuel (which would always be 7-C at minimum). A low-end would be pretending that saying that creating the combustible material requires almost zero energy, and you just need to heat it up enough to ignite (which would be really low). This is sort of a mid-end saying "A fire occupying that area takes that much energy, we don't know how they got that energy there, but it came from the character."

 

[KatBoi69]

It's not currently calculated as "Energy needed to heat the air to the temperature initiating combustion", it's "Heat energy that a fire occupying that area would have".

It's like, they're adding enough energy to create a fire through unknown means without needing an external source of combustion. A high-end would be doing E=MC^2 for creating the fuel (which would always be 7-C at minimum). A low-end would be pretending that saying that creating the combustible material requires almost zero energy, and you just need to heat it up enough to ignite (which would be really low). This is sort of a mid-end saying "A fire occupying that area takes that much energy, we don't know how they got that energy there, but it came from the character."

So chemically, if you do that mid-end calc described above, using Q=SM(delta)T, then you are calculation the energy required to heat the volume of air occupied by the fire to the temperature of that fire.

I think it would be seriously splitting hairs to say that a character doesn't get the AP of the explosion produced if they were generating fuel and then igniting it. Obviously the matter creation method would need specific context to apply a mass to energy conversion.

 

[Agnaa]

So chemically, if you do that mid-end calc described above, using Q=SM(delta)T, then you are calculation the energy required to heat the volume of air occupied by the fire to the temperature of that fire.

I think it would be seriously splitting hairs to say that a character doesn't get the AP of the explosion produced if they were generating fuel and then igniting it. Obviously the matter creation method would need specific context to apply a mass to energy conversion.

What is the difference between your suggestion here and what was outlined in the OP?

 

[KatBoi69]

What is the difference between your suggestion here and what was outlined in the OP?

I'm not proposing anything there. I'm saying that what we currently do implies that you should use the density of air, not fire, if you look at it from a scientific perspective.

If you use the density of fire for that calculation, it is considering the feat as, "character generates fire at ambient temp, then heats that fire to the temperature of fire."

If you use the density of air for that calculation, it is considering the feat as, "the character heats the air from ambient temp to the temperature of fire."

The second option seems more in line with how you conceive of the mid-level calc.

 

[Agnaa]

I'd word it more like "Character heats a portion of the volume typically indicative of the amount of that volume which fire occupies to the temperature of fire." Which seems better.

It's about getting the right end result, which is a certain amount of mass at a certain temperature.

 

[DontTalkDT]

Generally when you heat something you need to use the density of that thing it had when you measured its volume, which is dependent on its heat at that point in time.
So yeah, usually when doing fire you need lower density.
...and I'm not even quite sure for fireballs with how massive the air currents probably are...

 

[KatBoi69]

I'd word it more like "Character heats a portion of the volume typically indicative of the amount of that volume which fire occupies to the temperature of fire." Which seems better.

It's about getting the right end result, which is a certain amount of mass at a certain temperature.

That wording is a little complex, but I get what you mean.

As far as getting a right result, for what you're calculating, you have the "right" math. If you're choosing to calculate this as a heating feat, q=smt is the right move. The only thing preventing the answer from being correct is the interpretive part of "What density do I use?" Which requires nailing down the order of events in the specific feat.

Couple of notes: If you do this with the density of air, you'd get the same outcome here as you would for a heating feat. Irl, fire or an explosion would release more energy than just the heating.

 

[Agnaa]

So, I just learned of another alternate method of calculating fire, which has been used and (from a quick look) gives results 10.6x to 50x higher than the one discussed and accepted in this thread.

It is used in this calc and this calc.

The method takes the oxygen content of the air (20.95%), finds its density, and uses a "yield of burning oxygen" of 13062500 J/kg (I could not find a source for this number in the pages linked). One of the calculations (Spino's) assumed that the entire volume of air was made up of oxygen, resulting in a far higher result, and did so when calculating an explosion rather than a pillar of fire. This gives a result 216.6x and 764x higher than the ground-based and air-based explosion formulas respectively.

Pinging everyone who was involved in creating/accepting them: @Jasonsith @Spinosaurus75DinosaurFan @DMUA

Which method for calculating fire should be used? And can methods of calculating fire be used for explosions such as this one?

 

[Jasonsith]

Noted.

Will comment later.

For the Spider-Man one you just quoted...... Normally it is an air blast non-nuclear destruction or a ground blast destruction (use the ground blast overpressure method)

 

[Mariogoods]

I'm not that knowledgeable regarding this issue. However, it should be noted that the result would affect many current calculations, such as D&D fire spells (Here).

 

[DontTalkDT]

So, I just learned of another alternate method of calculating fire, which has been used and (from a quick look) gives results 10.6x to 50x higher than the one discussed and accepted in this thread.

It is used in this calc and this calc.

The method takes the oxygen content of the air (20.95%), finds its density, and uses a "yield of burning oxygen" of 13062500 J/kg (I could not find a source for this number in the pages linked). One of the calculations (Spino's) assumed that the entire volume of air was made up of oxygen, resulting in a far higher result, and did so when calculating an explosion rather than a pillar of fire. This gives a result 216.6x and 764x higher than the ground-based and air-based explosion formulas respectively.

Pinging everyone who was involved in creating/accepting them: @Jasonsith @Spinosaurus75DinosaurFan @DMUA

Which method for calculating fire should be used? And can methods of calculating fire be used for explosions such as this one?

Methods that use burning of something first and foremost require that something is burned. For something like a propane explosion that's fine (use the yield of burning propane, of course). For just air it would be hardly applicable. I doubt oxygen alone burns (exothermic).
Also to consider is that the energy comes from the chemical reaction, so it doesn't scale to the AP of the attacker.

So: If something is burned in a chemical reaction the energy from the reaction can be used. For everything else use flame heat + density of air at that heat together with the regular heat change formula to calc flames.

 

[Agnaa]

So with the way those calcs are done, they shouldn't be used, but something somewhat similar could be done for durability?

 

[DontTalkDT]

Probably? At a glance I think the propane one could easily be fixed by using the energy release of burning propane, though.

 

[Agnaa]

Well, I'm gonna try leaving comments on the calcs, and any derivative calcs, and try to get revisions for replacement calcs started for any verses that are based on these.

 

[Agnaa]

I believe I've found every calc that used that method. The vast majority of them weren't used on any mainspace pages, a D&D one was linked on the verse page but not used for any character ratings. OPM was hit hard, with 3 calculations for different tiers being affected. I have started a thread to revise it.

 

[DemonGodMitchAubin]

Does this effect anything that involves heat change with specifically only oxygen and nitrogen?

 

[Agnaa]

I don't really know what you mean. If it's something like "Created a box of oxygen that has a temperature of 1200 degrees", and you used specific heat capacity over that mass of pure oxygen, then no.

The earlier part just affected calcs using "density of air" instead of "density of flame" for generic calcs involving fire.

The more recent part just affected calcs using "deflagration of oxygen" for generic calcs involving fire/explosions.

If you had good reason for using oxygen/nitrogen, and you didn't touch the deflag values, it'd definitely be in the clear. If you had some justification but used it, it'd depend on the specifics.

 

[DemonGodMitchAubin]

I don't really know what you mean. If it's something like "Created a box of oxygen that has a temperature of 1200 degrees", and you used specific heat capacity over that mass of pure oxygen, then no.

The earlier part just affected calcs using "density of air" instead of "density of flame" for generic calcs involving fire.

The more recent part just affected calcs using "deflagration of oxygen" for generic calcs involving fire/explosions.

If you had good reason for using oxygen/nitrogen, and you didn't touch the deflag values, it'd definitely be in the clear. If you had some justification but used it, it'd depend on the specifics.

Well the calc I am referring too is about freezing a large fire that is already alight, sounds like this wouldn’t effect that, but I wanted to make sure

 

[Arkenis]

How many kg is this? It gives me 0.00000279833.
A 900c flame gives around 0.3kg/m. What am I missing here?

 

[Agnaa]

I don't know, I'm not familiar with that tool.

 

[Arkenis]

I don't know, I'm not familiar with that tool.

How should I do it? that tool is put here btw

If there's a better tool I can't find it.

 

[Agnaa]

Your issue is that you used Pascals for pressure instead of bars. With bars, 1100 degrees gives a density of ~0.28 kg/m^3, and 1200 degrees gives a density of ~0.26 kg/m^3.

Seems like that would be more accurate than a blanket 0.3 kg/m^3 for all fire calcs, but it's only about 10% off, not too important.

 

[Agnaa]

Since I better understand the deflag method now, I'll quickly post my issues on it before I head to bed in case there's a discussion while I sleep.

First the easy one; a lot of calcs treat the entire volume as being composed of oxygen, which is patently absurd.

A slightly harder one; even the ideal calcs that realise that oxygen is 20.95% of the air just stop there, instead of accounting for the temperature and lower density, using a density for oxygen of 1.3311 kg/m^3, instead of the more proper 0.08 kg/m^3 (the number mentioned in Spino's blog post, making these values ~16.6x off).

Finally, the hardest one to argue; it seems to me like this method is taking the energy that oxygen releases when it burns, but the issue is that the oxygen in an area is only fully used up (i.e. all of its energy is released) when the fire is extinguished, because at that point there's no more oxygen to take. It's not quite this simple IRL, as air will bring in more oxygen. But still, the general concept that all of the oxygen in the volume will have its energy released for the fire within one second is a very tough sell, imo. Practically, the exact amount used seems so hard to quantify that this method's unworkable.

For a more minor issue, since it's the energy released by the act of the fire burning the fuel and the oxygen, it's a pretty hard sell to say that a fire manipulator is responsible for it. I'd expect characters with fire manip to only be responsible for the fuel/ignition, not the oxygen used, and that they'd be shut down against characters who can remove all the oxygen from an environment, or in an environment without oxygen. But this would only apply to some cases, not quite invalidating the method against durability.

For those reasons, I expect this method, even if refined, to not be practically usable, and I know that the actual implementations of them on the wiki mishandled them to varying degrees, resulting in highly inflated results.

 

[DontTalkDT]

Since I better understand the deflag method now, I'll quickly post my issues on it before I head to bed in case there's a discussion while I sleep.

First the easy one; a lot of calcs treat the entire volume as being composed of oxygen, which is patently absurd.

A slightly harder one; even the ideal calcs that realise that oxygen is 20.95% of the air just stop there, instead of accounting for the temperature and lower density, using a density for oxygen of 1.3311 kg/m^3, instead of the more proper 0.08 kg/m^3 (the number mentioned in Spino's blog post, making these values ~16.6x off).

Finally, the hardest one to argue; it seems to me like this method is taking the energy that oxygen releases when it burns, but the issue is that the oxygen in an area is only fully used up (i.e. all of its energy is released) when the fire is extinguished, because at that point there's no more oxygen to take. It's not quite this simple IRL, as air will bring in more oxygen. But still, the general concept that all of the oxygen in the volume will have its energy released for the fire within one second is a very tough sell, imo. Practically, the exact amount used seems so hard to quantify that this method's unworkable.

For a more minor issue, since it's the energy released by the act of the fire burning the fuel and the oxygen, it's a pretty hard sell to say that a fire manipulator is responsible for it. I'd expect characters with fire manip to only be responsible for the fuel/ignition, not the oxygen used, and that they'd be shut down against characters who can remove all the oxygen from an environment, or in an environment without oxygen. But this would only apply to some cases, not quite invalidating the method against durability.

For those reasons, I expect this method, even if refined, to not be practically usable, and I know that the actual implementations of them on the wiki mishandled them to varying degrees, resulting in highly inflated results.

Wouldn't the energy released from "burning oygen" (in parenthesis as burning is defined as an exothermal reaction with oxygen and oxygen, as far as I am aware, doesn't react exotherm with itself) depend on which fuel you burn it with anyway? Pretty sure most flame attacks burn nothing.

 

[Arkenis]

funny enough for a calc im doing using Spinosaur fire page, I get

Orange Flames deep: 1100c

Density: 0.28kg/m3

Volume: 131,687,751,781.13cm3

Mass: 36872570498.7kg

36872570498.7kg * 919 j/kg * 1100c - 16c = 3.7274482e+16 or 8.9 megatons of tnt

@Spinosaurus75DinosaurFan Have I done something wrong or is this way just not accurate?

 

[Antoniofer]

I believe I've found every calc that used that method. The vast majority of them weren't used on any mainspace pages, a D&D one was linked on the verse page but not used for any character ratings. OPM was hit hard, with 3 calculations for different tiers being affected. I have started a thread to revise it.

Going with pages such as the Ghoul or Rothé (although, the Rothé counts with adifferent AP value, but has the likely on it), they scale to Burning Hands, spell that uses the same method as Fireball.

 

[Agnaa]

Arkenis, Anton: Both of those use a valid method. The D&D calc that needed changing was this one on Gorbel's self destruction.

DT: I would kind of expect that, but it wouldn't surprise me too much to find out it's wrong. Maybe it being wrong is why it was removed from Wikipedia's page on Fire? (The only source the calcs use for that number).

 

[AguilaR202]

If one is to say a fireballs AP= Energy needed to heat up air by 1000 C it should be kept in mind that the hotter air gets the lower it’s density becomes so an average density of air between initial and final temperature would be fair to use for these calcs imo.

 

[Agnaa]

If one is to say a fireballs AP= Energy needed to heat up air by 1000 C it should be kept in mind that the hotter air gets the lower it’s density becomes so an average density of air between initial and final temperature would be fair to use for these calcs imo.

I disagree, actually. Usually for these calcs we measure the fireball after its already been created, so we'd need to measure the density at that already-heated states.

There may be some niche cases where what you say would apply, but those can be handled on their own.

 

[Spinosaurus75DinosaurFan]

Sorry what are the conclusions/issues right now?