Dust explosions

Combustible materials like coal, flour etc., when "powdered" into dust clouds can be violently explosive. The modern science explanation (still quite within the understanding of a medieval philosopher) is that they have a high surface to volume ratio, so they burn up extremely quickly if they catch fire. The danger presented by dust explosions was apparently known in the middle ages (if the internet can be trusted...) and candles and flames of any kind were prohibited in flour mills. I was wondering if the phenomenon matches Ars Magica physics, in which case the following spells might be valid:

Apprentice's Artillery, CrHe Level 5
R: Sight, D: Mom, T: Ind
Creates a billowing cloud of fine flour dust -- several paces high, and several dozen paces wide. The cloud that lasts only a few hearbeats but if in this timeframe it comes into contact with even a small flame (including any fire spell cast in the following round, see below), it explodes in a powerful deflagration (how much damage? +30 seems the very minimum...).
Base 2 (create processed plant products) +3 Sight. Note that suspended flour dust occupies a lot of volume, so an Individual without size modifiers can still produce a pretty large cloud; and that it's canonical that Mom spells can last a round or so.

FarSpark, CrIg Level 5
R: Sight, D:Mom, T:Ind
Ignites anything extremely flammable -- including a flour dust cloud -- within Sight range.
Base 2 (ignite something extremely flammable) +3 Sight

I can totally picture a runaway Flambeau or Tytalus apprentice, with nothing more than a season's priming in Creo (a score of 5), blowing up an army this way!

This crops up every once in a while.

Can you source that?
As I think the Momentary definition says "The magic is gone in a moment and so cannot be dispelled" ArM p112.
If it cannot be dispelled then how could it be affected by another spell, it seems a contradiction?

Sure. Crest of the Earth Wave (corebook p.156) can travel up to 50 paces (Voice Range), and it travels 50 paces per round. I've seen other effects here and there, but I'm too lazy to look them up :slight_smile:

Note that the passage you are quoting, about momentary spells not being dispellable, should be taken in the context of the entire paragraph -- where the brief duration of the spell itself is contrasted with the permanent duration of its non-magical result.

Very much so yes.

Individual probably wont work, simply due to how it´s described, a single plant... Group needed.
Exactly how much material you get from that is still a bit on the shaky side but should at least be enough to create a very notable boom.

Aside from that, you should probably have +1 or even +2 for complexity as you need a totally perfect spread for it to really work.

Barely. Make it Diameter and have a constantly exploding fireball for 2 minutes... :smiling_imp:
Or you have it spread over a greater area(the complexity part will spread it out) and then light it up...
Hmm, that makes me wonder how this spell would work, i get the feeling it should produce Group/rd...

While a spark might be enough, it more probably wont be most of the time. It is NOT extremely flammable, it´s extremely combustible. I would say you need Base 4, might be able to get away with Base 3 but i wouldn´t bet on it.

Yes, I understand the context of the paragraph, a great example is Pit of the Gaping Earth. The magic is present for a moment, the flow-on effect persists. That is my baseline for clarifying a moment as too short to last many rounds, and it is stated by the guideline.

So I agree, but CotEW helps my point rather than yours. And sourcing a spell rather than a spell baseline is not a strong argument against a spell baseline.

Crest of the Earth Wave travels up to 50 paces and it occurs in 1 round, and nothing in the spell is present the next round. The spell description is written specifically to explain the effect, stating that the magic is no longer present, and the side effect of the magic creates the wave. It also states that the effect only lasts 1 round. The magic cannot be targeted at all as it is Momentary. The crest spell effect can be targeted in the same round.

That is fine for a spell which has flow-on consequences. Your Creo spell does not have an effect on the environment except for the material created, so once the magic disappears so does the dust. There is nothing left after the Moment to ignite. It is actually a point about Creo magic and Duration rather than anything else.

If you up the Duration to Diameter, then its fine.
If you add a Creo Ignem sub effect, with the additional mags, then it is fine.

Note that for multiple individual plants you need Group, but for a single "thing" made of plant products (e.g. a vegetarian meal), it's Individual (and you pay an extra magnitude). I would surmise a cloud of flour dust is a single thing.

Agreed. I think that you get at least 1/10th of a cubic pace of material from base Individual, or a Bridge of Wood would have to be thinner than that, which seems too thin to support an elephant. That would be about 150 pounds of flour, and a pound of flour "powers" several cubic paces (again, according to the internet...)

Do you? If it was that difficult, I would assume the risk of it happening accidentally would not be so high. Also, magic is good at doing "perfect" things as long as they are simple (a perfect sphere, a perfect mix of liquids etc.).

Hmm, I thought the whole thing really burnt up very very quickly?

This is a good point (and I just learnt the difference between flammable and combustible!). I just checked, and apparently oil and flour dust both have an ignition temperature around 400C; more precisely dust's between 360C and 380C, and oil's between 400C (canola oil) and 430C (olive oil). Given that a cloud of flour dust has a higher surface/mass ratio than an oil surface, and a lower ignition temperature, shouldn't it be at least as flammable? Hmmm, I really know too little of this. I know by experience that if you touch a flame to some oil, it will catch fire almost istantaneously, while parchment needs at least a second or two. But flour dust? I've never tried, nor do I intend to :smiley: But I'd say it should catch fire really quickly, or else it would not burn explosively.

So you are saying that the magic of Crest of the Earth Wave only lasts an instant, far less than a round, so that most of the effect takes place after the actual magic is over? I don't really buy that, as it would make Crest of the Earth Wave non-resistable. But I agree that one could interpret it your way.

However, look at Dance of the Staves, p.138, which "causes a ... wooden object to bend and lash about wildly for a few seconds and then stop suddenly". Surely the magic persists for those few seconds? Similarly, look at The Cloudless Sky returned (p.128) "The clouds take a few seconds to clear, during which time you must concentrate on them". And what about Gift of the Frog's legs? The target has up 10 seconds after the spell is cast to take his leap.

Yes you do. The risk of accidents is there, it´s not superbig but IF it happens, the result could be spectacular, so people are understandably VERY cautious about this even if it wont happen MOST of the time.
Yes i know magic is good at it, but i still think it needs +1 to make it.

Well, think about it this way, if you make a PoF with Diameter, fire is constantly created yes? :smiling_imp:
Ergo, this spell would constantly create the material for the Duration. :mrgreen:

Doesn´t work out quite that simply.

At the same time, you throw a lit cigarette into a petrol fuel tank, and the most likely outcome is that fire is extinguished. (do NOT try it however unless you KNOW what you´re doing!)

Having made flourbombs just like making many other very interesting things go boom(the phrase curiosity killed the cat might be a good description for me you know... well if it wasn´t for me always being very cautious, enough that i´ve never been hurt, although once it was a bit too close when a spark jumped much too far and ignited something too soon, but the shrapnel went elsewhere) i have at least done it...

And no, it generally doesn´t catch fire quickly or easily... Mmm i´m having a bit of trouble with explaining without placing a "how to" online, not really something i want to do. This is really where the thing about the spread having to be perfect comes in, you need enough fire at just the time when the spread is at the critical point, then it explodes. If the spread doesn´t reach the critical point while there is fire, or if the fire isn´t enough to cause the chain reaction that causes the explosion, then you have a lot of flour just floating down to the ground, possibly with some minor sparks and fizzling about burning up just a small portion of the material.
If you want a basic show and tell, read Terry Pratchett´s "Monstrous Regiment". It´s a fun book either way.

If the spread is too thin, the chain reaction will only burn up a little bit around the flame, if it´s too dense then there wont be enough oxygen mixed in for an explosive reaction so at most you will get some slowly burning material instead. At extreme, it might still even burn out all the material but it will take a LONG time to do so, a couple of minutes are quite possible if it can be made to stay dispersed in the air for so long.

I would say no to that at least.

An effect that lasts "a few seconds" is still within the same round. The flour spell as presented requires a spell cast the next round. That said, your examples prove that the spells in the book are not using the spell guidelines properly. Point well made, and I agree that if you use the spells as presented as examples there your spell is OK too. Gift of the Frog's legs makes a complete mess of Momentary as a duration.

However I think a new spell should be made to the strict guidelines, not the spells that have been inherited from past editions.

For the sake of clarity, I'm trying to make sense of how Momentary applies to all those spells too, given the text in the core rules. It appears broken.

I do not think it is reasonable for the guidelines to state that the spells cannot be dispelled and then have a spell like Gift of the Frog's Legs as presented. Or the guideline is wrong, and should be updated.

Mmm, more reading (this is really interesting!) and it appears that the ratio between the minimum explosive density and the optimal explosive density is about a factor TEN. So if you know what you are doing (which is admittedly a big if), it does not seem so hard to get things "right enough" that they'll serve your purpose. Making (palatable) wine or ale seems to allow a much smaller margin of error, and you need no extra magnitudes for that.

I'm not so sure. This is an interesting point. I thought that, barring explicit exceptions (e.g. some Aquam guidelines), a creation spell with a long duration would just create one thing and sustain it, rather than constantly creating more stuff. Though I'd be interested in counterexamples.

I guess that would be the case because there's very little oxygen to burn, since the petrol vapours have "pushed it" out of the tank. But with a suspension like flour dust it should not be a problem.

I think I understand what you are saying -- it's very much the same issue for most explosives, all the way up to nuclear bombs (though in that case we are talking about neutrons rather than oxygen). But, as I said, the range of flour densities that appears to work seems fairly broad, with a factor 10 between the minimum and the optimal (which makes me think there's probably at least another factor 10 between the optimal and the maximum). I'm not convinced at all about getting it right being so hard. Though if you say so from experience, I'm inclined to believe you.

Mmmm. Would you also require Group for a vegetarian meal like a lentil soup? That would seem to contradict the RAW, though I concede there's room for arguing.

I would interpret the "cannot be dispelled" differently. Try to look at the whole paragraph. To me it does not seem as if it's saying "it's so fast you can't dispel it". It's more like "keep in mind that if a fire burns your grog, once the grog is toast, you can't dispel it, because at that point the magic has already run its course".

I think the appropriate TeFo is CrAu. Base 3:Create a debilitating kind of air.Especially since it's flour suspended in the air and not flour in a sack and the idea is to fill a large space.

[strike]But isn't that just stating the really obvious? And if so the language is really dreadful.[/strike] just re-read, the dispelling relates specifically to using Creo Rituals, its kind of moot.

Read the very first statement in Momentary: "The spell lasts but a moment and then dissipates", and the example of rock that rolls down hill after being magically placed at the top is making a clear statement about when magic is in effect (the placement), and when nature takes its course (rolling down hill).

Didn't we have the exact same discussion last year?

Ah, here: https://forum.atlas-games.com/t/new-spell-in-memoriam-bakehouse/5677/8

This is a good point. I'm not sure I'm convinced, but the idea certainly has a lot of merit.

There's a note in Tales of Mythic Europe about creating flour dust for explosions magically (I can't remember the page number, but it's the section about the mill in the Viking raid story). There it says that flour is a processed product rather than a natural one, and therefore needs a finesse roll to create. No explicit finesse ease factor is given, but it's noted that flour dust sufficiently fine for an explosion is too high to be practically feasible.

Not sure I agree with that - processed product is a simple +1 magnitude on the He guidelines and fine is not the same as complex. Millers don't carve each grain of flour individually and if they want finer flour they set the millstones closer together.

Well, that's fair enough...I thought I was right at the time and it would be like that in my game, because what a normal person does (which is low finesse) doesn't create a flour fine enough to dependably explode, or people would have used it for assasinations in real life. Also, it's one of the few explosives you can have in Mythic Europe, since gunpowder style explosives don't work. So, it seem high finesse to me.