How explosive is Flour?

[Zelphas]

I'm DMing a group (3.5 edition) in a homebrewed setting. They are currently fortifying a small mountain town that has been attacked by several mobs of undead. In their search for "flammable things", the paladin found a bakery with several bags of flour. Their plan with this flour is to throw it down from the top of the chapel where they are holed up, and then light the resulting cloud with a torch.

My question to the playground is this: Exactly how much damage should this do? I talked about it with an engineer friend of mine, and he guessed that a flour explosion would be similar in force to a frag grenade, which translates to roughly 4d6 damage. The group is currently level 7 and none are massive optimizers, so 4d6 is a lot of damage to them.

Any ideas? Thanks!

[Zelphas]

Here's a video of Mythbusters lighting creamer on fire, which is at least similar to flour, in case anyone's interested:

http://www.youtube.com/watch?v=yRw4ZRqmxOc

[Mando Knight]

The group is currently level 7 and none are massive optimizers, so 4d6 is a lot of damage to them.

...Really? Not even a 7d6 Fireball?

[Zelphas]

...Really? Not even a 7d6 Fireball?

None of them are Wizards, and the Sorcerer is Illusion based, so... yeah. They're actually kind of unoptimized. Looking at that, though, 4d6 damage seems completely reasonable, and maybe even a bit on the light side.

[Feddlefew]

I'm DMing a group (3.5 edition) in a homebrewed setting. They are currently fortifying a small mountain town that has been attacked by several mobs of undead. In their search for "flammable things", the paladin found a bakery with several bags of flour. Their plan with this flour is to throw it down from the top of the chapel where they are holed up, and then light the resulting cloud with a torch.

My question to the playground is this: Exactly how much damage should this do? I talked about it with an engineer friend of mine, and he guessed that a flour explosion would be similar in force to a frag grenade, which translates to roughly 4d6 damage. The group is currently level 7 and none are massive optimizers, so 4d6 is a lot of damage to them.

Any ideas? Thanks!

.... How much flour are we talking? :smallconfused:

On the one hand, they need to survive the resulting fire ball before we start thinking about the damage from the shock wave.

Edit: A frag grenade explosion is different enough from a dust explosion that I think it makes a bad model. I don't know how to calculate the damage from a dust explosion.

Since they're not inside they won't have to worry about the church coming down on there heads- the pressure has somewhere to go without demolishing the building, although there's still going to be damage.

[Zelphas]

.... How much flour are we talking? :smallconfused:

On the one hand, they need to survive the resulting fire ball before we start thinking about the damage from the shock wave.

They have about 15 bags, 10 pounds each.

[Sidmen]

.... How much flour are we talking? :smallconfused:

On the one hand, they need to survive the resulting fire ball before we start thinking about the damage from the shock wave.

And what that shockwave will do to the church... The explosion will be quite big vertically (they're dumping it down from a roof, right?); and all that force will be applied evenly all across the walls of the poor medieval building.

[Kadzar]

And what that shockwave will do to the church... The explosion will be quite big vertically (they're dumping it down from a roof, right?); and all that force will be applied evenly all across the walls of the poor medieval building.
I'm not an expert on the matter, but that creamer explosion looked more combustive than explosive in nature. I have little doubt it will set the surrounding area on fire, but the actual blast probably isn't enough to do anything more than spread itself and maybe push apart a paper-thin structure.

[Feddlefew]

I'm not an expert on the matter, but that creamer explosion looked more combustive than explosive in nature. I have little doubt it will set the surrounding area on fire, but the actual blast probably isn't enough to do anything more than spread itself and maybe push apart a paper-thin structure.

Well, it depends on how much dust. It's not in a confined space, so it shouldn't be too bad. Not like this, anyway:

http://upload.wikimedia.org/wikipedia/commons/0/0f/Washburnamill.jpg

Yes, this is a flour mill exploding.

[Zelphas]

Yeah, exploding the church would be bad. I think they could possibly set parts of it on fire, though, if they're not careful (though it is made almost entirely of stone). I just want to know just how badly charred the undeads should be.

[TypoNinja]

Well, it depends on how much dust. It's not in a confined space, so it shouldn't be too bad. Not like this, anyway:

http://upload.wikimedia.org/wikipedia/commons/0/0f/Washburnamill.jpg

Yes, this is a flour mill exploding.

Yea flour(/dust) explosions are no joke, assuming its a good cloud. Sitting there in bags it's practically harmless.

The key is that as a large cloud all the flour is able to burn at once. Small size of individual particles maxizes surface area so all of it can be ignited simultaneously (or close to it anyway). This causes a massive overpressure wave. And if you pay attention to the highspeed shots on Mythbusters you'll know that its this wave that does most of the damage in an explosion.

Dropping it out the window right from the sack will not make a good boom. Its not spread out enough. Your players need to get creative with the delivery mechanism if they want to weaponize flour.

Mythbusters actually demonstrated it takes a bit of effort, they tried compressed air out of an oil drum and still got more of a big ball of fire than an actual "boom". Their cloud didn't disperse enough to give us an actual explosion.

[Zelphas]

Yea flour(/dust) explosions are no joke, assuming its a good cloud. Sitting there in bags it's practically harmless.

The key is that as a large cloud all the flour is able to burn at once. Small size of individual particles maxizes surface area so all of it can be ignited simultaneously (or close to it anyway). This causes a massive overpressure wave. And if you pay attention to the highspeed shots on Mythbusters you'll know that its this wave that does most of the damage in an explosion.

Dropping it out the window right from the sack will not make a good boom. Its not spread out enough. Your players need to get creative with the delivery mechanism if they want to weaponize flour.

Mythbusters actually demonstrated it takes a bit of effort, they tried compressed air out of an oil drum and still got more of a big ball of fire than an actual "boom". Their cloud didn't disperse enough to give us an actual explosion.

Point taken. I expect they're going to look up the dispersal themselves, and I told them to start coming up with ideas for the next session. I think they're looking for more of a "big ball of fire" at the moment; less damage to the church that way.

[Feddlefew]

Yea flour(/dust) explosions are no joke, assuming its a good cloud. Sitting there in bags it's practically harmless.

The key is that as a large cloud all the flour is able to burn at once. Small size of individual particles maxizes surface area so all of it can be ignited simultaneously (or close to it anyway). This causes a massive overpressure wave. And if you pay attention to the highspeed shots on Mythbusters you'll know that its this wave that does most of the damage in an explosion.

Dropping it out the window right from the sack will not make a good boom. Its not spread out enough. Your players need to get creative with the delivery mechanism if they want to weaponize flour.

Mythbusters actually demonstrated it takes a bit of effort, they tried compressed air out of an oil drum and still got more of a big ball of fire than an actual "boom". Their cloud didn't disperse enough to give us an actual explosion.

Usually what happens during the big dust explosions is a small fireball disperses the surrounding dust, leading to a second, much more powerful explosion. Of course this (to my knowlage) can only happen in a confined space, like the interior of a building.

[TypoNinja]

Usually what happens during the big dust explosions is a small fireball disperses the surrounding dust, leading to a second, much more powerful explosion. Of course this (to my knowlage) can only happen in a confined space, like the interior of a building.

The building probably acts as a container, without a building your dust cloud would simply disperse rather rapidly.

I'd imagine a dust explosion is a fine line between spread out just enough to burn rapidly and so spread out one piece of dust can no longer ignite its neighbor, or clumped up too much and its burns slowly as a solid instead of a dust cloud.

Still if the PC's determine that just a nice big fireball will do the job, it could be done if they kludge up some suitable dispersal method.

[Spuddles]

I'd have it to 2d6 or 3d6 of fire damage in an open space, reflex half.

Flour & creamer doesn't explode, per se, it just creates a giant fireball because it has an extraordinary surface area to flammable material ratio and is thoroughly mixed with oxygenated air. Explosions tend to happen in confined spaces- namely grain elevators.

And it definitely would not be comparable to a frag grenade. Those are very concussive explosions and are thoroughly mixed with exploding shrapnel. Burning fire is almost the on the opposite end of explosion types when compared PE creates in a frag grenade. Again, it just burns a whole bunch and isn't really creating a massive shockwave by expansion of superheated gasses in an iron cylinder.

[Slipperychicken]

It might deal a number of d6s equal to a Knowledge (Architecture and Engineering) check, divided by 10 and rounded down, with a reflex save for half. The check represents how well they manage to set it up. If they get less than 10 on the check, it is totally ineffective and doesn't deal any damage. Affected creatures which take fire damage must also succeed a DC 15 Reflex save to avoid catching fire.

The PCs also need to make a DC 20-25 Knowledge (Architecture and Engineering) check to know, in-character, that they can do this in the first place. Checks like that can help prevent many of the shenanigans your physics majoring players will try to come up with.

[LibraryOgre]

So, there's the time my group set a good chunk of Waterdeep on fire.

Right after 3.0 came out, I ran a scenario I wanted to for a while... namely, when they approached Waterdeep, I had a perfect storm of events conspire to utterly destroy the town (Halaster got taken by the Mists to Ravenloft, and some Talosians Earthquaked the entire town, now over an un-maintained catacomb of tunnels). The living population was forced outside of town, many of the Lords were missing or lost, and the monsters that HAD lived in Undermountain were boiling out of cracks in the ground.

The party opted to chase some orcs into a smithy, and noticed the orcs fleeing into an underground storage. Looking down, they saw that it was coal storage... the orcs had darkvision, and so had the dwarven owners, so an underground coal storage place was just fine.

The mostly human party said "Coal? Great. We'll just light some lamp oil and burn them out."
I looked at them and said the fateful words. "Are you sure."
"Yeah!"
"I have three words for you. Fuel. Air. Bomb."
Being kids from Kansas, where you get the occasional silo explosion, they cursed a lot and started making saving throws.

While limping away with 1 HP, they ran into the dragon. They survived by hiding a lot, and letting the flames cover their escape.

Then the Hobgoblin Imperium (recently established in the Neverwinter Woods) arrived to render aid, and things went to really weird.

[Zelphas]

@Slipperychicken: I like that idea. it makes sense with the rules, and I think the players can make it work. Thanks!

[cellingwood]

Wait, flour can really explode?
One of my friends was DMing a campaign when our party chased some cultists into a flour mill. Long story short, it caught on fire and blew up. We spent the next half hour laughing about the mill that had been completely leveled whilst the DM tried to restore order.
But you're all serious? I'll never look at bread the same way again!

[KillianHawkeye]

There's kind of a difference between flammable and explosive.

[holywhippet]

There's kind of a difference between flammable and explosive.

Consider gunpowder. It will happily burn without exploding in an open area. If you contain the burn though, that's when things go bad. For that matter, consider C4. You can actually safely burn the stuff. It require heat and pressure to detonate. There were some GIs in Vietnam who used to burn a bit of C4 to heat up their rations with. Some of them made the mistake of trying to stamp out the fire with their foot though, thus adding pressure as well as heat. In short, boom.

[cellingwood]

There's kind of a difference between flammable and explosive.

Ah, right.
I'm just saying, in the campaign that I played in, that mill totally blew up. My character avoided damage by diving into the basement and taking out the 4 or 5 cultists down there by himself (barbarian FTW).

[LibraryOgre]

Ah, right.
I'm just saying, in the campaign that I played in, that mill totally blew up. My character avoided damage by diving into the basement and taking out the 4 or 5 cultists down there by himself (barbarian FTW).

Like I mentioned, check out fuel air bombs and silo explosions. They don't happen all the time, but I would not be surprised at a mill exploding.

[AttilaTheGeek]

If they just toss a bag in the air, light it, and call it a day, I'd call it 1d6 or 2d6.

But on the other hand, if they tossed it down the steeple of the church, gave it a few seconds or a minute to really disperse, and then ignited it, that church is going down. As are the players' hit point totals.

[Feddlefew]

Consider gunpowder. It will happily burn without exploding in an open area. If you contain the burn though, that's when things go bad. For that matter, consider C4. You can actually safely burn the stuff. It require heat and pressure to detonate. There were some GIs in Vietnam who used to burn a bit of C4 to heat up their rations with. Some of them made the mistake of trying to stamp out the fire with their foot though, thus adding pressure as well as heat. In short, boom.

Well, an explosion is just a pressure wave- in this case caused by a rapidly expanding cloud of hot gas- so how powerful an explosion is depends on if the gas has somewhere to escape too and how much pressure is building up.

For instance, guns work because the hot gases from the combusting gunpowder can only escape by pushing the bullet out of the barrel. The same thing happens if you were to put something over the release valve on a gas cylander.

[TypoNinja]

Wait, flour can really explode?


Its not that flour explodes, its that any airborn dust can.

Very small particles mean that there is little/no energy lost to thermal dispersion when each individual piece is lit on fire, allowing for easy chain reactions.

If the dust cloud is spread out just right, that is far enough apart that everything's got enough room to burn freely without consuming the oxygen its neighboring pieces will need to combust, and still close enough together so that one piece can ignite another, then you get a boom.



Some of them made the mistake of trying to stamp out the fire with their foot though, thus adding pressure as well as heat. In short, boom.

Doubtful. C4 is ridiculously stable, that's why the military loves it. Its pretty much impossible to accidentally set off. Firing a gun at it isn't a sharp enough shock to set it off. I don't see a guy's boot doing the job.

[Killer Angel]

If the dust cloud is spread out just right, that is far enough apart that everything's got enough room to burn freely without consuming the oxygen its neighboring pieces will need to combust, and still close enough together so that one piece can ignite another, then you get a boom.

With a gust of wind, you should disperse the floor sufficiently well...

[Dewani90]

well, flour on fire might work but, how about something more consistent?, everyday items you can find even on a medieval kitchen, mixed in the propper amount could as well create powerful explosives, and I'm not talking about only fire damage, I mean the type of damage that makes enemies into tiny chunks of themselves scattered all over the place, I'm still researching what those ingredients are to use them on a campaign

[Scow2]

The PCs also need to make a DC 20-25 Knowledge (Architecture and Engineering) check to know, in-character, that they can do this in the first place. Checks like that can help prevent many of the shenanigans your physics majoring players will try to come up with.

What?! DC 20-25? This is a DC 10 check, DC 15 at most, for either (Architecture and Engineering) or (Local). Medieval societies built their flour mills and bakerys away from important locations because of their propensity for detonation.

[Slipperychicken]

What?! DC 20-25? This is a DC 10 check, DC 15 at most, for either (Architecture and Engineering) or (Local). Medieval societies built their flour mills and bakerys away from important locations because of their propensity for detonation.

DC 10 would mean that fully half (50%) or more of all people in the entire world know this fact, even those lacking Knowledge ranks. This is not the case.


Knowledge

Answering a question within your field of study has a DC of 10 (for really easy questions), 15 (for basic questions), or 20 to 30 (for really tough questions).

I'd say that when you need to use an internet advice forum for the answer to a question (and aren't just trolling) which needs more than two responses for consensus, the DC is at least 15.

[Feddlefew]

What?! DC 20-25? This is a DC 10 check, DC 15 at most, for either (Architecture and Engineering) or (Local). Medieval societies built their flour mills and bakerys away from important locations because of their propensity for detonation.

I'd go with DC 15 Knowledge (local) for knowing that it happens and DC 25 (Knowledge A & E) OR DC 20 Knowledge (alchemy) for knowing what the optimal conditions are to make it happen.

[Tvtyrant]

To get it mixed up correctly you could have an Air Elemental turn into their small tornado form and dump the flour into the tornado. Sacrifice a cheap summon for critical damage!

http://25.media.tumblr.com/tumblr_m8g680zfgS1ru0y9ko1_1280.jpg

[Slipperychicken]

To get it mixed up correctly you could have an Air Elemental turn into their small tornado form and dump the flour into the tornado. Sacrifice a cheap summon for critical damage!

http://25.media.tumblr.com/tumblr_m8g680zfgS1ru0y9ko1_1280.jpg

...and die from the explosion.

[Tvtyrant]

...and die from the explosion.

Fireballs and lightning bolts have plenty of range. Just fill up the tornado and run like heck. :smallwink:

[Squark]

Well, then the question becomes one of the gas composition of an air elemental, and the question of how those gasses would be dispersed in a funnel cloud.

[Coidzor]

DC 10 would mean that fully half (50%) or more of all people in the entire world know this fact, even those lacking Knowledge ranks. This is not the case.



I'd say that when you need to use an internet advice forum for the answer to a question (and aren't just trolling) which needs more than two responses for consensus, the DC is at least 15.

Using the form of society we live in as the base for what people would know in D&Dland is not always a good idea, mind. :smalltongue:

[Slipperychicken]

Using the form of society we live in as the base for what people would know in D&Dland is not always a good idea, mind. :smalltongue:

Good point. For D&Dlanders, DC 15 is "Cave bears live in caves (http://suptg.thisisnotatrueending.com/archive/1839136/images/1211983139444.jpg)", and DC 25 is "Bears hit things with their claws". So this flour business should be somewhere around 30 or so.

[Gnoman]

Doubtful. C4 is ridiculously stable, that's why the military loves it. Its pretty much impossible to accidentally set off. Firing a gun at it isn't a sharp enough shock to set it off. I don't see a guy's boot doing the job.

You're quite right. Stomping on burning C4 will not result in an explosion. It will, however burn through your boot and probably your foot.

[Beleriphon]

There were some GIs in Vietnam who used to burn a bit of C4 to heat up their rations with. Some of them made the mistake of trying to stamp out the fire with their foot though, thus adding pressure as well as heat. In short, boom.

That's not true, the Mythbusters did that one, they used power hammers and anvils to get pressure higher than you can ever manage with a boot. Even setting it on fire with gasoline and trying the same with an anvil and you just get a flat piece of C4. The moral of the story is that you can't ignite C4 without a blasting cap.

That said, the idea of exploding grain silos or flour mills are completely real things. It does require containing the flour dust in a contained space, you can achieve the same effect with lumber mill. Saw dust is super flammable, and inside a building can build up a whole lot of pressure. In open air you probably would just get this:

http://youtu.be/yRw4ZRqmxOc

If you watch what happens it just burns very fast from the ignition point. Its not an explosion by any means.

A better option if you can get it is to use bottles of cooking oil or alcohol to make molotov cocktails. Those actually are dangerous since they can burn very hot and if its oil damn hard to put out.

[TypoNinja]

That's not true, the Mythbusters did that one, they used power hammers and anvils to get pressure higher than you can ever manage with a boot. Even setting it on fire with gasoline and trying the same with an anvil and you just get a flat piece of C4. The moral of the story is that you can't ignite C4 without a blasting cap.

That said, the idea of exploding grain silos or flour mills are completely real things. It does require containing the flour dust in a contained space, you can achieve the same effect with lumber mill. Saw dust is super flammable, and inside a building can build up a whole lot of pressure. In open air you probably would just get this:

http://youtu.be/yRw4ZRqmxOc

If you watch what happens it just burns very fast from the ignition point. Its not an explosion by any means.

A better option if you can get it is to use bottles of cooking oil or alcohol to make molotov cocktails. Those actually are dangerous since they can burn very hot and if its oil damn hard to put out.

In all fairness, that kind of conflagration would probably be sufficient for their needs if they managed to aim it correctly.