The expert advice from Jeremy Crawford on the subject of whether the substance created by the Grease spell is flammable is that "If the grease spell created a flammable substance, the spell would say so. It doesn't say so. "
Thing is, the spell DOES say that it creates a flammable substance. The spell description explicitly says that it creates "slick grease". Grease is, inarguably, a flammable substance. Ask anyone who's ever worked as a cook. It's way more flammable than dry wood is, yet I hope no one needs to be told that wood can be set on fire, right https://9apps.ooo/?
And this is true of all spells. If you use the Fabricate spell to make something out of wood, no one would seriously argue that the creation isn't flammable just because it's not specifically mentioned in the spell's description.
The Control Weather spell does not explicitly state that the rain made from it can extinguish a camp fire, yet no one would seriously argue that it couldn't.
It would be absurd to expect every mention of "water" in a spell to include a part about how it can douse fire, just as it would be absurd to expect every mention of a flammable substance to include a part about how it is indeed flammable. So the "if the spell doesn't specifically say something then it doesn't do it" logic is just silly.
Only one out of three definitions of grease are inherently flammable. Oily matter is not defined and I can guarantee you, that there are heat resistant, non-flamable lubricants.
As the matter in the case of the Grease spell ist magical in nature, nothing indicates, that it really is flamable.
As said above, while cooking grease may be flammable, there are many other grease lubricants that are certainly designed to not combust for safety reasons. You wouldn't' want much of your machinery burning up because all its moving parts caught fire due to friction issues.
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"The mongoose blew out its candle and was asleep in bed before the room went dark." —Llanowar fable
Grease is often combustable, but it's not always (in fact rarely) flammable. If it was, we wouldn't cook with it or make tallow candles out of it. In fact, that demonstrates that grease hinders flame by slowing the rate a wick burns.
Grease can become flammable when heated to the point it begins to aerosolise and then you ignite that air/grease vapour mix (this is why deep frying frozen turkeys is a bad idea). Grease on itself, in the solid or viscous liquid form that it needs to be to act as a lubricant, is not flammable, it's combustible at best. Petroleum jelly, a grease that is literally made from petroleum, can be used to extinguish flames, yet is an excellent lubricant around the home.
1 - JC could possibly be the foremost expert on DnD design
2 - JC can also frequently contradict himself
3 - Many rules are explicit regarding what can and cannot be done
4 - Many rules are not
5 - There are more than one type of grease
6 - Magic is weird
7 - At your table, the Grease spell can make cooking grease that burns
Probably because of my background with machines, the first thing I think of when I read the Grease spell is a lubricant that wouldn't burn. Someone that likes to cook probably thinks of animal fat. I know people that thought of something like crude oil. Despite what Mr Crawford answered (somewhat smugly), the spell description does not provide all of the answers. Because, as you point out, water spells don't say the water puts our fires, and wood does not specify that it can burn. The firebolt spell says it ignites flammable objects. But not only do we not have a full list of what is and is not flammable, we aren't even given many rules for what something on fire actually means in game terms.
I suspect his answer has more to do with game balance than a sense of reality. If they say the grease is of the flammable nature, then they have to explain what effect that has. Does it set buildings on fire? How much damage do you take moving through it? Is it like 4 squares of alchemist fire? Now the spell has so many effects it might not be level 1 anyone.
So I think the only satisfying answer is that the Grease spell is not flammable in official games. In your home games, you can do whatever you want. Just be aware that it could result in many burned villages once your players get their hands on it.
Just be aware that it could result in many burned villages once your players get their hands on it.
I agree with you. I'd like to point out that a lack of flammable grease will not in any way prevent or deter a Murder Hobo from burning a village. I've been there.
Even flammable types of grease aren't all that flammable -- grease fires are usually either because the grease was extensively heated before igniting, or because it's mixed with something that provides a wicking mechanism, such as cloth or paper. I doubt treating it as equivalent to oil (flask) will break anything, though.
Even flammable types of grease aren't all that flammable -- grease fires are usually either because the grease was extensively heated before igniting, or because it's mixed with something that provides a wicking mechanism, such as cloth or paper. I doubt treating it as equivalent to oil (flask) will break anything, though.
Yeah, I agree treating it as oil and having it burn out like web will not break the game and in some ways makes the spell weaker.
It's honestly a style thing and depending on the player let them decide if their version of grease ignites or not. As I would with a monster if it were to use this spell as an ability. It could be also fun to make a scroll of grease that's been tweaked to be more flammable. Just as a bit of a more unique magic item.
Honestly, I generally don't put a lot of stock in anything that Jeremy Crawford says on his twitter. He comes at things very much as a player. I honestly think that's why there's so little official material that helps new DMs to figure out how to make judgements that are both fair but won't break the game. Sure, he might be lead rules designer and that's great. Frankly, I get the feeling he spends very little time and gives very little attention to what goes on in our side of the DM screen.
This is where I suggest a death of the writer approach.
Once the official sources are written and published that's where the writer's input stops. No writer can control how their work is interpreted. Tolkien for example repeated ad nauseam that the Lord of the Rings was not a world war allegory. That hasn't stopped large swathes of English and Literature academics finding such allegory.
If a writer has created something that is ambiguous then, do what we humans normally do...exercise our own judgement decide for ourselves how best to fill in the blanks. If grease as a spell doesn't say it's flammable (or not) then it's your call as DM how it works. Jeremy Crawford and the other writers had their chance to have a say before putting out their material. Now that it's out in the world their contribution is over. It's entirely your call and you have no need to explain beyond that.
If players question your call, then explain that well this guy was the one who has allowed the ambiguity in the first place. His opinions amount to just that...opinions unless they appear in an official sourcebook that your group is using. Extending that out, it's also up to your group which source books you choose to use. I frequently stick to only the PHB, DMG and MM. This makes it all financially more accessible for players, but also easier to get to grips with the way the game works. If a group have gotten a good chunk of the way into a campaign and it is felt by everyone that more is needed then we can add in a different sourcebook too, otherwise, no need to complicate things.
There's a group I watch where there was an instance of poorly-placed grease spell + poorly-aimed flame spell + ill-advised water spell. Much hilarity (and friendly-fire😜 damage) ensued and is considered to be the educational part of that adventure of why you don't throw water on a grease fire.
If you don't like JC's feedback because it stuffs your fun into a box, you are not required to accept it. Just make sure your players know what they're getting themselves into before they choose a spell they expect to be nonflammable because JC said so.
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Human. Male. Possibly. Don't be a divider. My characters' backgrounds are written like instruction manuals rather than stories. My opinion and preferences don't mean you're wrong. I am 99.7603% convinced that the digital dice are messing with me. I roll high when nobody's looking and low when anyone else can see.🎲 “It's a bit early to be thinking about an epitaph. No?” will be my epitaph.
There's a group I watch where there was an instance of poorly-placed grease spell + poorly-aimed flame spell + ill-advised water spell. Much hilarity (and friendly-fire😜 damage) ensued and is considered to be the educational part of that adventure of why you don't throw water on a grease fire.
If you don't like JC's feedback because it stuffs your fun into a box, you are not required to accept it. Just make sure your players know what they're getting themselves into before they choose a spell they expect to be nonflammable because JC said so.
Is that Oxventure? The one where Luke DMs? So much fun 'now you're a bear on fire!'
I have been asking people if they think the grease should be flammable based on the spell description. I was curious if it really just came down to what they imagined when they heard the word 'grease.' It pretty much does, though one did ask if the grease in question was created, or summoned from somewhere.
But I did also discover a clue to what type of grease the spell conjures. In the spell itself. It has a material component.
The expert advice from Jeremy Crawford on the subject of whether the substance created by the Grease spell is flammable is that "If the grease spell created a flammable substance, the spell would say so. It doesn't say so. "
Thing is, the spell DOES say that it creates a flammable substance. The spell description explicitly says that it creates "slick grease". Grease is, inarguably, a flammable substance. Ask anyone who's ever worked as a cook.
Cooking oil and fats certainly respond to high temperatures, but don't always necessarily erupt in flame, certainly not to the effect that I imagine in my mind's eye, which is like Create Bonfire. Even if it was called Chip Pan Oil, it's still magical, not mundane, and will have different effects as a result. Just because Eldritch Blast does magical force damage, it cannot target objects and thus can't break open a door or punch a hole through paper (much to the delight of stationary shops everywhere).
It's way more flammable than dry wood is, yet I hope no one needs to be told that wood can be set on fire, right?
And this is true of all spells. If you use the Fabricate spell to make something out of wood, no one would seriously argue that the creation isn't flammable just because it's not specifically mentioned in the spell's description.
I suppose if they listed the properties of wood it would take up a gigantic amount of space in the spell text, you're right, but even then what are you turning the wood into? Depending on the wood, its shape and depth, it may not burn all that quickly or efficiently. It depends on what purpose you want to burn it for: I imagine most people who want to burn Grease are those who want to light those standing on it on fire, or some other instantaneous effect.
The Control Weather spell does not explicitly state that the rain made from it can extinguish a camp fire, yet no one would seriously argue that it couldn't.
Again, I'd argue that this affects something that already exists, rather than creating an entirely new effect, which Grease does. The Grease from the pork rind or butter, if we're using spell components, is not the kind of Grease that is summoned because it is in no way - as written - flammable.
It would be absurd to expect every mention of "water" in a spell to include a part about how it can douse fire, just as it would be absurd to expect every mention of a flammable substance to include a part about how it is indeed flammable.
You wouldn't use water to put out an electrical fire, or indeed a grease fire, but then that's bringing in real world chemistry to D&D and that's as dangerous a mix as water on a grease fire. Well, probably not. It's also incredibly pedantic of me, so for that I apologise.
Even then there's very deliberate usage of language when it comes to ignition: Fire Bolt does not ignite objects worn on a character, but Fireball does; if magic is meant to do something, it's usually reflected in the language.
So the "if the spell doesn't specifically say something then it doesn't do it" logic is just silly.
I wouldn't say it's silly, but if Grease is flammable in your game that's absolutely fine. The thing about this post is I'm absolutely fine with Grease being flammable, it just won't do much more damage than Create Bonfire and it'll cost a spell slot, so it might end up being a bit of a waste depending on the kind of fireball I deem it necessary to erupt into, if any. I guess that's why it's not flammable: how much damage would it do, at what radius, and be enough to justify a 1st level spell slot in addition to its usual effects? One could improvise damage, but then we're back to square zero: what the DM says goes.
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Zero is the most important number in D&D: Session Zero sets the boundaries and the tone; Rule Zero dictates the Dungeon Master (DM) is the final arbiter; and Zero D&D is better than Bad D&D.
"Let us speak plainly now, and in earnest, for words mean little without the weight of conviction."
If one sticks a red-hot piece of iron in a tub of lard, that lard will boil, and flames will erupt, but not in a fireball. Pull that hot iron out, or let it cool in the lard, and the lard will go out. In solid or liquid form, without adding more flammable chemicals, lard, vegetable oil, and diesel fuel will only burn in the presence of another heat source. If any of these are spread on a floor surface, for example, the smear will only burn for as long as one holds a torch to it. The flames will not spread on their own. (Edit: A splintered, pine floor or a floor of woven grass mats would arguably create a candlewick effect; a very slow start, easy to extinguish at first, that builds until the fuel [including the floor and other combustibles] is gone.)
Now if someone were to heat that lard to liquefy it (or use a liquid oil), then run it through a high-pressure pump, through an atomizing nozzle, and provide a heat source like a road flare, then one would effectively have a continuous fireball emanating from the tip of that nozzle.
Grease can be made to burn very hot, but under natural conditions it is extremely reluctant to burn at all. If one wants to magically create a grease spell with a napalm sample as the spell component, then who am I to tell them they can't do that? There, now you can set the floor on fire, and everyone passing through that fire will not only suffer those consequences, but leave sticky, flaming tracks behind them a few steps as they slip and slide down the corridor, screaming; their shoes ablaze.
When actually dealing with fire safety there's three temperatures for a liquid: the flash point (if you apply a spark, you'll get ignition), the flame point (it will keep burning for more than a few seconds), and the self-ignition point (it will ignite spontaneously). A material is classed as flammable if it's flash point is less than 100F.
No commonly used cooking grease is flammable. The figure I find for lard is 390F. Which is certainly achievable when cooking, or it comes in contact with an external fire source for an extended period, but not a situation that's likely to occur spontaneously.
That's pretty interesting information. I think that brings us back to one of the problems with the natural language approach of the rules. (I prefer it overall, but it does leave some ambiguity and occasions of weird wording).
The firebolt spell says it ignites flammable objects. I think a lot of people use a broader definition of flammable. It is casually used to mean 'things that burn when fire is placed on it.' Most people probably read the firebolt rules and figure you could start a campfire with it. Wood and pinestraw is flammable right?
But according to the definition you show here, wood would not be considered 'flammable,' because the flashpoint is far higher than 100 degrees.
But according to the definition you show here, wood would not be considered 'flammable,' because the flashpoint is far higher than 100 degrees.
I think the rules for solid materials are different, but it's true that applying a spark to a solid wooden object will not generally ignite it, unless it's tinder. I suspect giving a damage threshold for ignition is the easiest.
But according to the definition you show here, wood would not be considered 'flammable,' because the flashpoint is far higher than 100 degrees.
I think the rules for solid materials are different, but it's true that applying a spark to a solid wooden object will not generally ignite it, unless it's tinder. I suspect giving a damage threshold for ignition is the easiest.
But according to the definition you show here, wood would not be considered 'flammable,' because the flashpoint is far higher than 100 degrees.
I think the rules for solid materials are different, but it's true that applying a spark to a solid wooden object will not generally ignite it, unless it's tinder. I suspect giving a damage threshold for ignition is the easiest.
At the very least the wood would have to be very dry with a large surface area (like kindling, sawdust, or brush wood) to qualify as flammable. Honestly, that is probably a better definition to use in game since a healthy tree or treated furniture are not likely to be ignited by the likes of a firebolt.
The expert advice from Jeremy Crawford on the subject of whether the substance created by the Grease spell is flammable is that "If the grease spell created a flammable substance, the spell would say so. It doesn't say so. "
Thing is, the spell DOES say that it creates a flammable substance. The spell description explicitly says that it creates "slick grease". Grease is, inarguably, a flammable substance. Ask anyone who's ever worked as a cook. It's way more flammable than dry wood is, yet I hope no one needs to be told that wood can be set on fire, right https://9apps.ooo/?
And this is true of all spells. If you use the Fabricate spell to make something out of wood, no one would seriously argue that the creation isn't flammable just because it's not specifically mentioned in the spell's description.
The Control Weather spell does not explicitly state that the rain made from it can extinguish a camp fire, yet no one would seriously argue that it couldn't.
It would be absurd to expect every mention of "water" in a spell to include a part about how it can douse fire, just as it would be absurd to expect every mention of a flammable substance to include a part about how it is indeed flammable. So the "if the spell doesn't specifically say something then it doesn't do it" logic is just silly.
That is all.
grease
a: rendered animal fat
b: oily matter
c: a thick lubricant
Only one out of three definitions of grease are inherently flammable. Oily matter is not defined and I can guarantee you, that there are heat resistant, non-flamable lubricants.
As the matter in the case of the Grease spell ist magical in nature, nothing indicates, that it really is flamable.
As said above, while cooking grease may be flammable, there are many other grease lubricants that are certainly designed to not combust for safety reasons. You wouldn't' want much of your machinery burning up because all its moving parts caught fire due to friction issues.
Grease is often combustable, but it's not always (in fact rarely) flammable. If it was, we wouldn't cook with it or make tallow candles out of it. In fact, that demonstrates that grease hinders flame by slowing the rate a wick burns.
Grease can become flammable when heated to the point it begins to aerosolise and then you ignite that air/grease vapour mix (this is why deep frying frozen turkeys is a bad idea). Grease on itself, in the solid or viscous liquid form that it needs to be to act as a lubricant, is not flammable, it's combustible at best. Petroleum jelly, a grease that is literally made from petroleum, can be used to extinguish flames, yet is an excellent lubricant around the home.
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A few things can be simultaneously true.
1 - JC could possibly be the foremost expert on DnD design
2 - JC can also frequently contradict himself
3 - Many rules are explicit regarding what can and cannot be done
4 - Many rules are not
5 - There are more than one type of grease
6 - Magic is weird
7 - At your table, the Grease spell can make cooking grease that burns
Probably because of my background with machines, the first thing I think of when I read the Grease spell is a lubricant that wouldn't burn. Someone that likes to cook probably thinks of animal fat. I know people that thought of something like crude oil. Despite what Mr Crawford answered (somewhat smugly), the spell description does not provide all of the answers. Because, as you point out, water spells don't say the water puts our fires, and wood does not specify that it can burn. The firebolt spell says it ignites flammable objects. But not only do we not have a full list of what is and is not flammable, we aren't even given many rules for what something on fire actually means in game terms.
I suspect his answer has more to do with game balance than a sense of reality. If they say the grease is of the flammable nature, then they have to explain what effect that has. Does it set buildings on fire? How much damage do you take moving through it? Is it like 4 squares of alchemist fire? Now the spell has so many effects it might not be level 1 anyone.
So I think the only satisfying answer is that the Grease spell is not flammable in official games. In your home games, you can do whatever you want. Just be aware that it could result in many burned villages once your players get their hands on it.
I agree with you. I'd like to point out that a lack of flammable grease will not in any way prevent or deter a Murder Hobo from burning a village. I've been there.
Even flammable types of grease aren't all that flammable -- grease fires are usually either because the grease was extensively heated before igniting, or because it's mixed with something that provides a wicking mechanism, such as cloth or paper. I doubt treating it as equivalent to oil (flask) will break anything, though.
Yeah, I agree treating it as oil and having it burn out like web will not break the game and in some ways makes the spell weaker.
It's honestly a style thing and depending on the player let them decide if their version of grease ignites or not. As I would with a monster if it were to use this spell as an ability. It could be also fun to make a scroll of grease that's been tweaked to be more flammable. Just as a bit of a more unique magic item.
Honestly, I generally don't put a lot of stock in anything that Jeremy Crawford says on his twitter. He comes at things very much as a player. I honestly think that's why there's so little official material that helps new DMs to figure out how to make judgements that are both fair but won't break the game. Sure, he might be lead rules designer and that's great. Frankly, I get the feeling he spends very little time and gives very little attention to what goes on in our side of the DM screen.
This is where I suggest a death of the writer approach.
Once the official sources are written and published that's where the writer's input stops. No writer can control how their work is interpreted. Tolkien for example repeated ad nauseam that the Lord of the Rings was not a world war allegory. That hasn't stopped large swathes of English and Literature academics finding such allegory.
If a writer has created something that is ambiguous then, do what we humans normally do...exercise our own judgement decide for ourselves how best to fill in the blanks. If grease as a spell doesn't say it's flammable (or not) then it's your call as DM how it works. Jeremy Crawford and the other writers had their chance to have a say before putting out their material. Now that it's out in the world their contribution is over. It's entirely your call and you have no need to explain beyond that.
If players question your call, then explain that well this guy was the one who has allowed the ambiguity in the first place. His opinions amount to just that...opinions unless they appear in an official sourcebook that your group is using. Extending that out, it's also up to your group which source books you choose to use. I frequently stick to only the PHB, DMG and MM. This makes it all financially more accessible for players, but also easier to get to grips with the way the game works. If a group have gotten a good chunk of the way into a campaign and it is felt by everyone that more is needed then we can add in a different sourcebook too, otherwise, no need to complicate things.
DM session planning template - My version of maps for 'Lost Mine of Phandelver' - Send your party to The Circus - Other DM Resources - Maps, Tokens, Quests - 'Better' Player Character Injury Tables?
Actor, Writer, Director & Teacher by day - GM/DM in my off hours.
There's a group I watch where there was an instance of poorly-placed grease spell + poorly-aimed flame spell + ill-advised water spell. Much hilarity (and friendly-fire😜 damage) ensued and is considered to be the educational part of that adventure of why you don't throw water on a grease fire.
If you don't like JC's feedback because it stuffs your fun into a box, you are not required to accept it. Just make sure your players know what they're getting themselves into before they choose a spell they expect to be nonflammable because JC said so.
Human. Male. Possibly. Don't be a divider.
My characters' backgrounds are written like instruction manuals rather than stories. My opinion and preferences don't mean you're wrong.
I am 99.7603% convinced that the digital dice are messing with me. I roll high when nobody's looking and low when anyone else can see.🎲
“It's a bit early to be thinking about an epitaph. No?” will be my epitaph.
Is that Oxventure? The one where Luke DMs? So much fun 'now you're a bear on fire!'
DM session planning template - My version of maps for 'Lost Mine of Phandelver' - Send your party to The Circus - Other DM Resources - Maps, Tokens, Quests - 'Better' Player Character Injury Tables?
Actor, Writer, Director & Teacher by day - GM/DM in my off hours.
I have been asking people if they think the grease should be flammable based on the spell description. I was curious if it really just came down to what they imagined when they heard the word 'grease.' It pretty much does, though one did ask if the grease in question was created, or summoned from somewhere.
But I did also discover a clue to what type of grease the spell conjures. In the spell itself. It has a material component.
- A bit of pork rind or butter -
So that's one question answered at least :D
Cooking oil and fats certainly respond to high temperatures, but don't always necessarily erupt in flame, certainly not to the effect that I imagine in my mind's eye, which is like Create Bonfire. Even if it was called Chip Pan Oil, it's still magical, not mundane, and will have different effects as a result. Just because Eldritch Blast does magical force damage, it cannot target objects and thus can't break open a door or punch a hole through paper (much to the delight of stationary shops everywhere).
I suppose if they listed the properties of wood it would take up a gigantic amount of space in the spell text, you're right, but even then what are you turning the wood into? Depending on the wood, its shape and depth, it may not burn all that quickly or efficiently. It depends on what purpose you want to burn it for: I imagine most people who want to burn Grease are those who want to light those standing on it on fire, or some other instantaneous effect.
Again, I'd argue that this affects something that already exists, rather than creating an entirely new effect, which Grease does. The Grease from the pork rind or butter, if we're using spell components, is not the kind of Grease that is summoned because it is in no way - as written - flammable.
You wouldn't use water to put out an electrical fire, or indeed a grease fire, but then that's bringing in real world chemistry to D&D and that's as dangerous a mix as water on a grease fire. Well, probably not. It's also incredibly pedantic of me, so for that I apologise.
Even then there's very deliberate usage of language when it comes to ignition: Fire Bolt does not ignite objects worn on a character, but Fireball does; if magic is meant to do something, it's usually reflected in the language.
I wouldn't say it's silly, but if Grease is flammable in your game that's absolutely fine. The thing about this post is I'm absolutely fine with Grease being flammable, it just won't do much more damage than Create Bonfire and it'll cost a spell slot, so it might end up being a bit of a waste depending on the kind of fireball I deem it necessary to erupt into, if any. I guess that's why it's not flammable: how much damage would it do, at what radius, and be enough to justify a 1st level spell slot in addition to its usual effects? One could improvise damage, but then we're back to square zero: what the DM says goes.
Zero is the most important number in D&D: Session Zero sets the boundaries and the tone; Rule Zero dictates the Dungeon Master (DM) is the final arbiter; and Zero D&D is better than Bad D&D.
"Let us speak plainly now, and in earnest, for words mean little without the weight of conviction."
- The Assemblage of Houses, World of Warcraft
If one sticks a red-hot piece of iron in a tub of lard, that lard will boil, and flames will erupt, but not in a fireball. Pull that hot iron out, or let it cool in the lard, and the lard will go out. In solid or liquid form, without adding more flammable chemicals, lard, vegetable oil, and diesel fuel will only burn in the presence of another heat source. If any of these are spread on a floor surface, for example, the smear will only burn for as long as one holds a torch to it. The flames will not spread on their own. (Edit: A splintered, pine floor or a floor of woven grass mats would arguably create a candlewick effect; a very slow start, easy to extinguish at first, that builds until the fuel [including the floor and other combustibles] is gone.)
Now if someone were to heat that lard to liquefy it (or use a liquid oil), then run it through a high-pressure pump, through an atomizing nozzle, and provide a heat source like a road flare, then one would effectively have a continuous fireball emanating from the tip of that nozzle.
Grease can be made to burn very hot, but under natural conditions it is extremely reluctant to burn at all. If one wants to magically create a grease spell with a napalm sample as the spell component, then who am I to tell them they can't do that? There, now you can set the floor on fire, and everyone passing through that fire will not only suffer those consequences, but leave sticky, flaming tracks behind them a few steps as they slip and slide down the corridor, screaming; their shoes ablaze.
When actually dealing with fire safety there's three temperatures for a liquid: the flash point (if you apply a spark, you'll get ignition), the flame point (it will keep burning for more than a few seconds), and the self-ignition point (it will ignite spontaneously). A material is classed as flammable if it's flash point is less than 100F.
No commonly used cooking grease is flammable. The figure I find for lard is 390F. Which is certainly achievable when cooking, or it comes in contact with an external fire source for an extended period, but not a situation that's likely to occur spontaneously.
That's pretty interesting information. I think that brings us back to one of the problems with the natural language approach of the rules. (I prefer it overall, but it does leave some ambiguity and occasions of weird wording).
The firebolt spell says it ignites flammable objects. I think a lot of people use a broader definition of flammable. It is casually used to mean 'things that burn when fire is placed on it.' Most people probably read the firebolt rules and figure you could start a campfire with it. Wood and pinestraw is flammable right?
But according to the definition you show here, wood would not be considered 'flammable,' because the flashpoint is far higher than 100 degrees.
So then we have to wonder, how hot is a firebolt?
I think the rules for solid materials are different, but it's true that applying a spark to a solid wooden object will not generally ignite it, unless it's tinder. I suspect giving a damage threshold for ignition is the easiest.
That's a pretty good idea.
At the very least the wood would have to be very dry with a large surface area (like kindling, sawdust, or brush wood) to qualify as flammable. Honestly, that is probably a better definition to use in game since a healthy tree or treated furniture are not likely to be ignited by the likes of a firebolt.
How 'bout, "Hot enough to ignite a lamp wick or a patch of prepared tinder, but too short-lived to ignite anything more substantial."