5
\$\begingroup\$

A lot of my party's (3rd level) casters have something of a predilection for the Firebolt cantrip. Like some other fire-damage spells, Firebolt's description specifies that:

A flammable object hit by this spell ignites if it isn’t being worn or carried.

I'd love to give my players some of the flavourful utility that this description encourages: 'You miss the goblin, but you hit the crate he's hiding behind and now it's on fire.'

I'm aware of the general rules for hitting and destroying objects, which are covered under Statistics for Objects on p.246 of the DMG. I'm specifically interested in how these rules can be best applied (or overhauled) for the purpose of setting flammable objects on fire in a way that's fun, intuitive and easy to manage. Specific questions I have include:

  • Should flammable objects be vulnerable to fire damage?
  • Should fire-damage spell attack rolls have advantage against flammable objects?
  • How should the ongoing damage of something being 'on fire' be adjudicated?
  • Is the descriptor 'flammable' applied to objects at the DM's discretion?
\$\endgroup\$
5
  • \$\begingroup\$ Related, but not magnificently helpful: How fast does fire spread? \$\endgroup\$
    – Lovell
    Apr 25 at 11:17
  • \$\begingroup\$ Also related: Flamable vs. combustible \$\endgroup\$
    – Lovell
    Apr 25 at 11:18
  • 3
    \$\begingroup\$ I've voted to close for opinion-based, but if others disagree please remember to answer with support showing what you've used or seen used and why it's simple. \$\endgroup\$
    – NautArch
    Apr 25 at 13:08
  • \$\begingroup\$ Also related for guidance: How does fire work in D&D?. Possible duplicate \$\endgroup\$
    – NautArch
    Apr 25 at 13:53
  • 1
    \$\begingroup\$ Voting to reopen. I think this question can be answered in a way that -- with the support of experience -- satisfies the good subjective/bad-subjective criteria. (I myself have an answer I could contribute.) \$\endgroup\$
    – screamline
    Apr 25 at 22:07
2
\$\begingroup\$

Fun is subjective, but the rules supply a few tools that can be used to manage flammable objects intuitively and easily.

Let's start by acknowledging the elephant in this room: looking for rules to cover every detail regarding flammable objects is bound to be an exercise in disappointment. The rules don't spell out every interaction that can occur at your table. They leave a lot up to the DM to decide.

The rules do tell us, however, that the DM's job is to adjudicate damage to objects using common sense:

When characters need to saw through ropes, shatter a window, or smash a vampire's coffin, the only hard and fast rule is this: given enough time and the right tools, characters can destroy any destructible object. Use common sense when determining a character's success at damaging an object. Can a fighter cut through a section of a stone wall with a sword? No, the sword is likely to break before the wall does.

DMG p. 246.

I'll reiterate that once more. The rule is to apply common sense.

With that in mind, here's how I have handled flammable objects. It might look like a lot of words, but the mental processes I'm describing are quick.

First, I use the DMG's optional rule on Hitting Cover (p. 272). A spell like firebolt that misses because of an AC bonus from cover can hit whatever is providing the cover. In the question's example, the crate providing cover to the goblin could be hit if the caster's attack roll was close enough. The crate is an object. Firebolt says it ignites flammable objects. So, consulting my common sense, I ask: is this crate flammable? Is it made of wood, or something else that burns as readily as wood? Unless I can think of a good reason why the crate wouldn't ignite -- it's made of stone or metal, it's soaking wet, etc. -- it does. If I'm uncertain, I consult the rules on Objects (DMG p. 246) and compare the attack roll to the object's AC. Most of those ACs are fairly low already (especially the most flammable objects: cloth, paper, and rope are all AC 11), so I've seen no need to bother with advantage.

Next, to determine how affected objects are damaged, I use the rules on Dungeon Hazards (DMG p. 105) and Improvising Damage (DMG p. 249). I've found this works well enough whether I'm dealing with a single firebolt to a wooden door or a fireball that just ignited every unattended object in the room and created a raging inferno.

Hazards "are functionally similar to traps," which have save DCs set out in a table. The lowest save DC is 10. But saves against fire effects generally rely on Dexterity, and objects generally can't move, so I just have all objects automatically fail. I determine the damage they take using the Improvising Damage table -- but it's almost always the smallest amount, 1d10, which I average to 5. (For comparison's sake, one of the examples of a damaging effect at this level of damage is being "[b]urned by coals," DMG p. 249.) That's 5 fire damage each round -- which I apply at the start of the caster's turn -- until the fire is put out.1

The rules on Objects tell us that "fragile" objects of any size from Tiny to Large have 5 or fewer HP on average. In other words, I can conveniently assume that the first round of damage is enough to destroy most objects that are flammable (again, according to common sense) and less than "resilient." Resilient objects have enough HP to survive an additional 1 to 5 rounds (based on size), and so can be saved if the fire is put out quickly (although in my experience, PCs seldom bother).

Although the DMG suggests that "[p]aper or cloth objects might be vulnerable to fire and lightning damage" (p. 247), I haven't found that to matter. It'll all burn quickly enough just using these rules.

Finally, as the DMG notes (id.), Huge and Gargantuan objects present different issues. I typically don't use the approach I've described here for them. They need to be handled on a case-by-case basis. "[O]ne torch can burn a Huge tapestry," but a Huge statue might be so massive that superficial fire damage won't meaningfully affect it.

1For what it's worth, this approach is generally consistent with the fire elemental's Touch attack, which ignites flammable objects. The attack's description says "Until a creature takes an action to douse the fire, the target takes 5 (1d10) fire damage at the start of each of its turns." Technically, that means targets that are objects would need to have turns in the initiative order. I don't bother with that and instead apply the fire damage at the start of turn belonging to whatever creature caused the effect. I'm not interested in tracking initiative for chairs and tables. But YMMV.

\$\endgroup\$
3
  • \$\begingroup\$ Are you suggesting to apply the guidance on direct attacks in objects to accidental shots when you miss past them? \$\endgroup\$
    – NautArch
    Apr 26 at 18:21
  • \$\begingroup\$ Apologies, but I'm not 100% sure what you're asking. I'm suggesting using the Hitting Cover rule. If I'm uncertain whether an object hit by a fire attack would ignite (whether the object was hit accidentally or not), I use object ACs as a reference. Most of the materials with high ACs are materials I consider not to be flammable. \$\endgroup\$
    – screamline
    Apr 26 at 18:30
  • \$\begingroup\$ I had looked at that rule, too. I just wasn't sure it would apply for things missed 'behind' the target or if it should work the same way. If you've used it in this manner and can talk about hitting things that you didn't actually aim for at all, I think that'd help. That was my issue when thinking of the theoretical use of the variant cover rule. \$\endgroup\$
    – NautArch
    Apr 26 at 18:31
3
\$\begingroup\$

Fun Question

For your specific points:

  • Flammable is not the same as Vulnerable. Flammable means it can be set on fire without significant effort. Vulnerable indicates something especially damaging to the target. Wood-pulp paper is both flammable and Vulnerable to fire; humans are flammable but not Vulnerable; ice is not flammable but is Vulnerable to fire.
  • No, fire spells should not (usually) have Advantage on attacks against flammable targets. Secondary effects do not make it easier to hit a target. The flammability is activated by appropriate sources of fire damage, not by hitting a specific AC. In the hypothetical case of a golem with a high AC from numerous layers of well-spaced paper, fire attacks would probably have Advantage, but that is a specific situation in which the nature of a flammable object would counteract AC, making certain attacks more likely to connect and cause damage.
  • The mundane flask of oil (Player's Handbook, page 152, Oil) has guidelines for mundane fire. Taking 5 damage per round, until the fire burns out, is serious enough to be a threat but mild enough to not ruin a campaign. If you extend this rule to other flammable objects then you will need to house rule fitting durations.
  • Yes, flammable applies at the DM's discretion. Common sense and consistency are important when making such rulings (else your players will become frustrated, angry, and / or despondent about interacting with flammables). It is also worthwhile to do some independent research for how flammable likely targets are; I mistakenly believed spider webs were flammable for a few years until I did research and some experimentation and learned that spider webs are not flammable.

My own experiences, on both sides of the DM screen, have shown me that one of the best ways to handle "accidental" combustion is to give the most inconvenienced parties a metagame resource, such as Inspiration, to reward the players for going along with the change. When the player characters are inconvenienced by the fire, this acknowledges the increased challenge and incentivizes them to deal with it. When the NPCs are inconvenienced by the fire, giving the NPCs Inspiration mitigates the effectiveness of the "burn everything" tactic in a way that lets the players succeed but still be aware that not all the advantages go to the player characters.

Good luck!

\$\endgroup\$
0
\$\begingroup\$

I think simple is best. The DM can decide what items are affected by the spell, and which of those items are flammable.

If it is a medium or smaller flammable object, I usually just treat it as if a flask of oil was poured and lit there. Maybe have it last only 1 round for a tiny object, or longer if it is more substantial (e.g. a wooden chest).

Larger objects may be only partially on fire (flames in one 5' square), or if it was an AoE spell like Fireball, the whole thing might now be a flaming hazard.

\$\endgroup\$
3
  • \$\begingroup\$ Can you please add some support to this answer through use of your recommendations experienced or seen used? Covering what works, what doesn't, and what your experience was would help improve this answer. \$\endgroup\$
    – NautArch
    Apr 26 at 18:42
  • \$\begingroup\$ I think simple is best. Sure I could pad my answer with a myriad of stuff, but my point is clear (and simple), and adding a bunch of unnecessary verbiage would not improve the point, and would contravene the point of the answer. I think simple is best. Overthinking is the problem. (Which is a symptom of this entire Stack -- way too much overthinking here.) \$\endgroup\$
    – PhilB
    Apr 27 at 1:30
  • \$\begingroup\$ How has this affected your game? How has this ensured fun, or perhaps for what kind of players/table has this ensured fun? How simple has this been to actually run? Has it been intuitive to your players? \$\endgroup\$
    – Someone_Evil
    Apr 27 at 11:26
0
\$\begingroup\$

It's important to find the fun for your table before putting much effort into mechanics

A key observation in this case is that D&D 5e doesn't simulate much around causing or spreading fires in combat, which matters because there aren't very many mechanics around those things. As you've noted, the core rulebooks generally only go as far as indicating that an object could be lit on fire if it's flammable.

That's the first big consideration: detailed mechanics around how things burn (how easily they ignite, how quickly they are destroyed by fire, how fire might naturally spread around the area) don't really exist, and so neither do applications of those properties. So before working out a detailed system to apply those properties it's worth considering why it will be worth your (and your players') attention to interact with them. And with homebrewed mechanics that can get really table-specific and so it's a great opportunity to create something tailored to your players.

For example, if your players have fun preparing battlefields with hazards and like the idea of preparing burn zones mid-combat, then details like how easily or how quickly fire spreads from one object to another would be important to focus on and how much damage an object takes from being on fire may be less so. Then it's more a question about what types of objects PCs might be interested in moving around and burning and less about how durable they are to flames.

My players definitely like getting extra mileage out of their spells, including starting fires, but they are not so interested in very precise object interactions like burnability of random objects. So for my players it would be too fussy and niche-applicable to worry about those kinds of details, and it would degrade the game to spend time modeling and considering them all the time. We still do all kinds of fire-related stuff, but I fold it into the streamlined nature of 5e: things ignite, or don't, producing environmental hazards; interacting with burning objects grants Advantage (like when trying to break down a door) or Disadvantage (like when trying to do investigate the interior of a building that's on fire); fire damage translates directly to what a fire from Create Bonfire would do; and other things like that.

But that's us, and other tables might not have as strong a preference for ease and fluidity of play versus more number-crunching content.

I do not recommend developing and choosing mechanics in a vacuum, then seeing what happens; I recommend thinking about what you want to be possible (but currently isn't) and then create new mechanics to make it possible.


In games that I run, my players try to get all kinds of extra benefits out of spell effects. That very much includes fire and heat. But what I have discovered my players most want are, in roughly this order, to:

  1. Think of clever solutions to problems that use their characters' special abilities
  2. Overcome in-game obstacles more easily than what they assume the intended approaches would allow
  3. Do things with some extra dramatic flair

I'll give two examples of fire spells in this context from a game I'm running now.

Case 1:

In the first case, the PCs were sneaking into a building to steal some sensitive documents and discovered a prisoner caged in the office they were ransacking. My most fire-happy player decided that they should steal the documents and free the prisoner, then use a fire to destroy the evidence. I ruled that it worked, but that the fire quickly spread out of control and engulfed the entire building. The flammability of the building created a narrative situation in which they had an effective time limit to escape alive, and with certain routes blocked off due to a new environmental hazard. Plus lots of complications after the fact.

In this case, more specificity wouldn't have made the encounter more interesting but definitely would have multiplied the amount of work I had to do. Tracking the flammability of the wooden desk vs. the wooden floor vs. the bookshelves would have added a lot of bookkeeping, and what I would have gained from it would have been a more slowly-spreading fire (and therefore fewer complications to the encounter) and a more formulaically-spreading fire. More predictability and less peril is not what I was going for. Even if I had had house rules for flammability of all objects in place, I would have thrown them out for this sequence.

What I ended up choosing interacted with elements 1 and 3 from my list: fire magic made hiding evidence easier, and was certainly dramatic. But while the player expected to get 2 as well (no evidence, we'll be totally in the clear!), they got the opposite. Which also made sense in-game, as that character had no expertise in forensic fire investigation and should not be able to casually predict exactly how a flammable building will ignite.

Case 2:

The same party in the same game came upon a locked vault door with very little time to break in but a strong interest in doing so. They had not prepared enough to get into the vault by any means I had planned, and a vault door that can be casually bypassed at any time may as well not be there at all. They learned through investigation that the most vulnerable part of the vault door was a collection of hinge mechanisms that would be very hard to destroy in the time they had available. A player came up with the idea of using magical fire to heat the hinge mechanisms and make them easier to break.

That's not too realistic, but I ultimately said yes: PCs attacking a hinge mechanism in the middle of a bonfire got to attack with Advantage. It was a novel use of the PC's magical abilities (item 1), helped them deal with an obstacle in a novel way (item 2, and especially important as they had no other way of getting in), and was dramatic (item 3). It doesn't matter that thick metal objects aren't flammable, or that I didn't have a full suite of mechanics dealing with heating metals. The party got to solve their immediate problem with creative use of the resources at their disposal. The mechanics of how that played out were the least important part of what was a tense and fun encounter.


Regarding the specific questions posted in the OP:

  • Should flammable objects be vulnerable to fire damage?

I say that this one is largely irrelevant. Objects being destroyed or not by the end of combat usually doesn't matter at all, and consequently neither does how quickly or easily an object is destroyed. In cases where this does matter (and you could definitely engineer as many of these as you like), the challenge is almost certainly going to come from issues that surround the object's destruction. Those are in your hands as DM, and creating the scenario will require you to account for this one way or another.

As an example, if your players need to destroy a flammable object within 10 turns to accomplish their objective, and vulnerability to fire would make that too easy to do, then you would either need to increase the object's HP, introduce other obstacles which prevent the PCs from igniting it too early in the combat (or something similar), or choose to use a non-flammable object instead. Any such mitigation would just make the vulnerability irrelevant. So this idea, to me, just feels like mechanic and bookkeeping bloat.

  • Should fire-damage spell attack rolls have advantage against flammable objects?

As with the previous bullet point, I don't think that it matters. But if pressed to it I'd say no. An attack roll for a fire spell is usually to see if the spell itself hits in a meaningful way, not to see if the target ignites. If you miss with Firebolt, the bolt of fire doesn't hit what you were trying to hit. Being flammable alone doesn't make a target easier to hit, only easier to set ablaze if it is hit.

If you have flammability as an option with meaningful gameplay benefits and a fire-happy table of players, you are already in for a lot of fires. Granting Advantage to efforts to start fires will exacerbate this while also making those benefits easier to gain. But if you're ready for those, then I don't think that this one would matter much either way as it would be subsumed by encounter design concerns.

  • How should the ongoing damage of something being 'on fire' be adjudicated?

I, personally, just treat burning objects as though they were in the middle of a fire created by the most basic casting of the Create Bonfire spell but without the opportunity for a Saving Throw. If something is on fire, it can't dodge the heat or flames! So it's generally 1d8 per turn.

  • Is the descriptor 'flammable' applied to objects at the DM's discretion?

Of course. The word flammable itself is a kind-of-subjective term: many things will burn in the right conditions, but most people are concerned with the conditions they are most likely to encounter. Water isn't generally thought of as flammable, but hurl a chunk of cesium into it and you'll see it "burn". Wax candles are designed to burn in everyday conditions, but a candle in a vacuum will never ignite in candles' usual way.

The importance of whether or not an object is described as flammable can only be evaluated in the context of how important you have decided a burning object will be. But I do not think that a DM adding or removing that description from objects will, in itself, have much material effect on the game.

\$\endgroup\$
-8
\$\begingroup\$

Spells only do what they say they do. Unless they say they ignite things on a miss, they don't.

In general, in DnD 5e, spells only do what they say they do, and no more. Unless they explicitly state that they'll light nearby objects on fire on a miss, they won't. If you attack a goblin with Fire Bolt and miss, it'll fizzle out, because it doesn't specify any rules for collateral damage. The only time it will ignite flammable objects is when it's being used to deliberately target them, and the only reason it can ignite objects at all is because it explicitly states it can.

\$\endgroup\$
8
  • \$\begingroup\$ That was not, what OP asked. Lovell explicitly asked what he could do to flavor up/utilize effects like ignition of flammable objects through spells like Firebolt to make the game more interesting for his players. \$\endgroup\$ Apr 25 at 14:58
  • 3
    \$\begingroup\$ Also, there is a recurring problem of 5e answers on RPG.SE parroting the supposed wisdom that "spells do only what they say they do and nothing more." See, e.g., this meta Q&A. In actuality, the principle is "spells do only what they say they do, and anything else is up to the DM." That is especially relevant here, where the querent is the DM at their table. \$\endgroup\$
    – screamline
    Apr 25 at 15:12
  • \$\begingroup\$ @screamline Of course the GM can houserule additional effects for spells. The GM can hand out unicorns and lollipops for all the players or decide to kill them all with an avalanche of rocks from the sky, too. When we're talking about the games rules, though, we're talking about the things written in the books. \$\endgroup\$
    – nick012000
    Apr 25 at 15:41
  • 3
    \$\begingroup\$ @nick012000 True, but OP was explicitly asking, what he could do to solve that by home-brewing. \$\endgroup\$ Apr 25 at 16:00
  • 3
    \$\begingroup\$ @nick012000 This question is essentially asking, "The rules are a floor; as DM, where should I put the ceiling?" Insisting that the floor is the ceiling is not a useful answer, as the downvotes here are signaling. \$\endgroup\$
    – screamline
    Apr 25 at 17:17

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.