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Scenario:

A large number of barrels filled with beer are at the entrance to a path into the mountains. Three trolls protect it. As other troll creatures approach they are given a barrel and they head down to the 'event'

Question

The players have a plan to set fire to it, to cause a distraction. I know that spirit based alcohol is flammable and would go up with a bang.

The wooden barrels are flammable, but I can't find out if beer is. As the ABV would potentially be something quite low (3.6% to 4%) I am not sure it would burn quickly

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    \$\begingroup\$ I am the DM for this adventure \$\endgroup\$ – JPuk Oct 6 at 13:34
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    \$\begingroup\$ it is with natural fire, as we are playing in a very low magic fantasy world \$\endgroup\$ – JPuk Oct 6 at 13:36
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    \$\begingroup\$ @Gandolf989 If you have an answer, you should post it below. Comments containing answers (including the “have you considered…?” kind), are removed for being in the wrong section. \$\endgroup\$ – SevenSidedDie Oct 7 at 21:16
  • \$\begingroup\$ @JPuk: Please edit any necessary clarifications into the question itself. :) \$\endgroup\$ – V2Blast Oct 8 at 6:01
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Liquids with less than 40% alcohol aren't really flammable. While wood is flammable, since it's filled with liquid it won't burn either.

Then again, the explosion of a fireball could probably blow the barrels apart, spilling beer all over. As a distraction that would still work.

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    \$\begingroup\$ Beer barrels used to be proofed against liquid penetration because tannins is not what you want in your beer. Still, this process, and huge amount of cool liquid makes the wood hard to set on fire. \$\endgroup\$ – Mołot Oct 6 at 14:00
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    \$\begingroup\$ blow the barrels apart, spilling beer all over That would be a great tragedy. FWIW, if we are going by a tight rules interpretation, fireball doesn't create any over pressure the way a conventional bomb or grenade does, it simply sets flammable things on fire (per the rules text). Any DM can rule otherwise if they so choose. Welcome to RPGSE. Please take the tour and visit the help center to see how this Q&A site works best. \$\endgroup\$ – KorvinStarmast Oct 6 at 16:43
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    \$\begingroup\$ To be fair a barrel full of beer will burn, until the fire breaches its integrity.most of the wood is not wet. \$\endgroup\$ – John Oct 6 at 17:18
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    \$\begingroup\$ @John Actually, no! This works on the same physics as the leather cauldron (look that one up if you want, it's pretty cool). The wood will char away (or burn, possibly) until it reaches the point where the fluid inside is wicking away the heat faster than then fire is adding it, at which point the wood stops burning and the beer starts boiling away instead. Now that MIGHT be a thin enough layer of wood that it's no longer structurally able to support the fluid, I don't know exactly, but I suspect you'd do nothing more than blacken the barrel while the beer boils off. \$\endgroup\$ – Darth Pseudonym Oct 7 at 13:55
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    \$\begingroup\$ @DarthPseudonym The problem is the leather caudron is leather is porous enough to soak through, a barrel is not (which is one of the reasons we use them) Now yes oak does not burn quickly (the russians used it for reentry shielding for a reason) so it is possible to boil the liquid before it breaches, but depending on the wood it is also possible to burn the wood enough it fails under the load it is bearing first. \$\endgroup\$ – John Oct 7 at 14:00
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Beer isn’t flammable and neither are barrels

Flammable materials have a flash point less than 37.8oC (100oF). For practical purposes, a substance is flammable if brief contract with an ignition source (a spark, a flame or a Fireball) will cause it to ignite and sustain combustion after the source is removed.

Beer isn’t, nor are any alcoholic beverages - even spirits have to be heated to well above 37.8oC before the can be ignited. Pure or near pure ethanol (alcohol) is flammable. Petrol is flammable but diesel isn’t.

Similarly, timber (in the form of barrels or houses or otherwise) isn’t flammable. Wood shavings and sawdust may be but solid pieces of wood aren’t - you can’t light a barrel by briefly touching it with a lit match. For that matter, neither are candles as anyone who’s had to light a birthday cake can attest.

Now, there are plenty of things that will burn if you get them hot enough. Trees and houses burn but they aren’t flammable. Aluminium and steel burn - aluminium more readily than steel which is why you have to weld it with an Argon shield; if you don’t it catches on fire.

As a rule of thumb, if you have to hold a match to it for more than a few seconds, it isn’t flammable.

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    \$\begingroup\$ I can light even weaker absinthe on fire by briefly touching it with a match, so "pure or near pyre ethanol" is kinda opposite to my real experience. Also, your definition of flammable has nothing to do with the question. "The players have a plan to set fire to it, to cause a distraction." — they may have many rounds, or minuets, to do it. Maybe more, who knows? \$\endgroup\$ – Mołot Oct 7 at 0:18
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    \$\begingroup\$ I feel like using a United States safety definition isn't meaningful in context. In the real world, wood is often called "flammable" even though its flash point is far higher (500+°F). That said, most of D&D history also allowed Fireball to melt gold, etc. from heat, and used the term "combustible", and that disappeared with 4E ("A globe of orange flame coalesces in your hand. You hurl it at your enemies, and it explodes on impact.") and 5E uses "flammable". So this definition may be fairly accurate anyways. \$\endgroup\$ – MichaelS Oct 7 at 11:09
  • \$\begingroup\$ @Mołot I think the real boundary is somewhere around 60%. Some homemade spirits can be lit as well. \$\endgroup\$ – Tomáš Zato Oct 7 at 12:16
  • \$\begingroup\$ @TomášZato Yes. Proof spirit is about 60% alcohol (actually 57%), and was originally tested for by soaking a pellet of gunpowder in the spirit. If the gunpowder still burnt, the spirit was proof. (See wikipedia.) \$\endgroup\$ – Martin Bonner supports Monica Oct 7 at 16:55
  • \$\begingroup\$ 151 proof rum will ligh with very little effort from the match holder. Flaming shots for the win! \$\endgroup\$ – KorvinStarmast Oct 7 at 17:43
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Depends on what kind of game you want

The realistic approach

As the other answers already said, real life's beer isn't really flammable. Apparently, the barrel themselves won't be either. So if the wizard cast a Fireball in the trolls' reserve, nothing would happen. This approach would be realistic (but a bit anticlimactic IMHO).

The gaming approach

I must admit : if years of gaming learnt me anything, it's that barrels containing a potential combustible explode when damaged (warning: TvTrope link). Your barrels might not be red with yellow/black stripes but if I heard "alcohol barrels" and "fireball", I wouldn't even think about "is it flammable though ?".

Bonus point : the trolls' beer approach

Real beer isn't flammable, okay, but why would the trolls have a stock of low-alcohol beer ?

  • Trolls are big : they would need a lot more of alcohol to be drunk than humans. You tend to be "tipsy" between 0.6 and 1 gram of alcohol for every liter of blood. A typical human has a blood volume of 5 liters. So, to be tipsy, an adult human would need between 3 and 5 grams of alcohol. Using the cube-square law and the grid, we can extrapolate that the blood volume of a troll would approximately 8 times the human's volume (if a human is a cube of 1x1x1, a troll is a 2x2x2). So, if a troll is tipsy, it means they would have consumed between 24 and 40 grams of alcohol.

  • Trolls regeneration : This ability is often pictured as a quicker metabolism. I'm not a biologist but if it's indeed faster, their alcohol assimilation should be too.

Basically, trolls' organism should be more efficient to reduce the active alcohol in their bloodstream and need more of it to have any effect. There is so much type of beer, crafted by many culture, it shouldn't be that surprising that trolls found a way to boost the ethanol production to get f*cked up.


I think the rule of cool apply here. Your group's plan sounds good, especially if they try this as a diversion and not as a fighting advantage : using those "exploding/flammable beer barrels" might unbalance fights but I can't see any problematic consequences saying the barrels burn for few turns before they break. Then, if the group is far enough, you might not even have to worry if there should be a flaming wave of beer, an explosion or just a disappointing soaking of the reserve's ground.

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  • \$\begingroup\$ @SevenSidedDie I didn't mean "combustible" in a scientific way : diesel isn't a combustible either apparently but I'll call bullsh-t if a barrel of it doesn't explode when I shoot it. Also, I don't think trolls would be interested in small beer : their regeneration is often described as a quicker metabolism than humans. I'm not a biologist but if it is quicker, I think their alcohol assimilation would be too. Being Large, they would also need more alcohol to be drunk. In those condition, it seems impossible for them to be drunk with this (and even Trolls wouldn't drink it just for the taste) \$\endgroup\$ – Nahyn - support Monica Cellio Oct 7 at 17:05
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    \$\begingroup\$ If that interpretation of the question is part of the logic supporting answer, you can edit to include it. The question only says “beer”, but you make a good case that troll “beer” is likely to be high-proof even if the DM in the question hadn’t thought of that yet. (If I recall correctly, high-alcohol drinks being called “beer” is historically attested, so that could be used to strengthen that sub-argument too if you can find a good source. A quick search didn’t get me one.) \$\endgroup\$ – SevenSidedDie Oct 7 at 17:49
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They might, if for no other reason because it's not such a terribly bad idea, and it works with the plot. It's a better plan than shouting and kicking in the front door, anyway.

D&D 5e is less specific, but up to at least 3.5 the descriptions of fire-based spells such as Burning Hands explicitly said in their decription:

Flammable materials, such as [...] thin wood burn if the flames touch them.

So, one may conclude that D&D generally considers wood to be flammable, within limits (note the word "thin"). Arguably, the staves of a barrel are thin-ish, so that would do.

In reality, barrels are often made out of oak, and oak is pretty poor at quickly catching fire. Oh sure, it does burn, finally, it's just that holding your lighter up to it for a few seconds won't do much but scorch the surface a bit.
Plus, combustion is bound to temperature, and a beer-filled barrel has a huge volume of thermal absorbant (beer) inside. That will make it even tougher to really "burn" other than getting scorched very superficially.
The beer itself will not burn, even if it's a Bulldozer-alike. You can quickly ignite (for half a second or so) watery liquids containing 35-38% of alcohol, but to truly burn, it needs to be above 50%. Something 5-10% alcohol? No way.

But then, it's a game, games are about having a fun experience, and trolls don't know that barrels don't burn well. Nor do we know what kind of dwarf piss an average troll considers "beer". Might well contain 50% alcohol.

So if you can successfully trick those trolls by burning some barrels, why not. Maybe the players should add a few handfuls of straw or cloth and spill a little oil to account for, uh, the overall physical correctness and to please the nitpickers in the group. But in general, I see no objection.

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