Dust explosions

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.

I think it's definitely right that a finesse roll is needed - there's some room for debate on what its level should be, but flour is an artifical product, and therefore needs a finesse roll by page 77 of the main book.

If I was the magus designing the spell I think I'd try to define the geometry at that stage rather than leaving it to finesse at casting. X number of tetrahedrons made of flammable plant material of side Y in a face centered cubic arrangement of unit side Z. Platonic forms are easy for creo and you don't want to be able to vary Y and Z at the time of casting so if there is a finesse roll required it will be low.

If you are trying to improvise a dust explosion then yes, high finesse is called for, and probably a check on natural philosophy or milling or baking (or mining if you are a terram specialist using coal dust) as well.

Yeah, i´m not really sure which would be correct. Canon spells/guidelines end up on both sides.
In this case it would be a matter of there always existing X individuals of flour in the air, if it´s exploded it´s gone so the spell compensates by remaking it. If you throw barrels of water over a big CrIg fire, will you be able to put the fire out before the Duration of the spell creating it is over? I would most certainly say "NOT a CHANCE!".
So i´m actually not at all sure how to handle a situation like this.

Nope. :mrgreen:
It´s because except under certain circumstances, the cigarette isn´t hot enough to cause ignition. Lack of oxygen for the reason you guessed can contribute however.

Outside of optimal you might still have something that burns more or less, but you´re unlikely to get anything resembling an explosion.

I probably would.

Not so sure about that.

Mechanically, the fact that an explosion is big (area of effect) does not mean it has an impressive damage.

What does hurt more IRL? Being struck a sword blow, or being near a flour dust explosion? I don't know, but I don't think the "damage" is very different, and, given the chance, I'd avoid the sword blow.

=> I'd say probably more something like "Does +10 damage to all in x area, which must also make a Str roll of difficulty 9 to avoid being blown back, 12 to avoid falling over". It might also destroy/damage buildings, as per the rules in LoM

If you want a high ignition method it might be better to soak people in auto-replicating lamp oil (diameter duration) and set them on fire with the spark. Higher level, that is sure, though.

I also think that +30 is really high. being trespassed from side to side by a foot-wide javelin of stone only causes +10 damage. +30 is equivalent to being hit by a LAVA flow. I think that the extra damage in a dust explosion is because of the flying shrapnel that it causes when it blows stuff from the things around it in a confined space, not because the explosion is specially powerful in an open environment. As a related note, people did not fear (much) canon balls in the napoleonic naval battles, they feared the wood shrapnel the canon ball created.


Hardly. Your suggestion might work very well for persons that are some distance AWAY from the explosion, but if you´re inside a dust explosion this big, you´re either extremely lucky or you die, end of story.
The fire part would probably be enough for +5-10 damage by itself, but it´s the shockwave that kills.
Standing inside a large dust explosion would be something like having several hand grenades explode at maybe 2m distance in a cluster around you. Hit by shrapnel or not wont make much difference, the combined shockwave is deadly most of the time.

Remember, a small dust explosion is enough to make a silo or a mill to become 100% wrecks, and this spell would use over 100 times more material, even at the low end. 1/10th of a barrel of flour is enough to destroy a normal wood building if it explodes inside.

Only reason this was never historically used for anything is because it´s so hard to cause the explosion when you want it, it´s highly unpredictable and even an error in the spread so minor you cant see it can make it into a slow burning fireball or make it not catch fire at all. But when it explodes optimally, it´s no different from any slow(like cordite) to medium(black powder) type explosives. Only thing you wont get from it is something like really fast explosives, like Pentyl or similar(8400m/s).

I am not much into pyrotechnics, but isn't it ^RECISELY because it is an enclosed space that you can have an explosion? IIRC if you have a bunch of blackpowder and ignite it, it just burns fast, while if you do the same with the powder in a contained space it goes BOOM. It might be that the same happens with an enclosed space like a mill or silo?


Confining burning gunpowder gives you explosion in two ways.

  1. it confines the heat and gas of the burning gunpowder so the temperature + pressure increases which increases the rate at which the gunpowder burns which means it burns hotter in a positive feedback loop - this is the main reason. This is also why a straw fuse filled with gunpowder is faster than the same amount of gunpowder laid out in a line.*
  2. The heat and pressure is not felt outside the container until it bursts releasing them all at once giving a nice sharp shockwave.

Given the spread out nature of a fuel-air explosion factor 1. can't really come into play because by the time the heat reaches the confinement most of the burning has already happened. A fuel-air blast gives a much longer pulse of overpressure which does not shatter resistant materials but pushes over walls and fills space. This makes it useful against cave complexes because the energy follows the tunnels rather than being wasted making gravel. (a bit like an AD&D 2E fireball :smiling_imp: )

  • This is also why, if you are cooking your dinner over a bit of burning C4, you should not stamp on the fire to put it out :open_mouth:

I will say I do like this argument. I am not a huge fan of the idea of a flour explosion, it seemed cumbersome the last time it was discussed, but I absolutely LOVE it's use in the fiction I have read and I can see it being a story "moment" where a dice roll would hinge the entire event. A botch would be insane and imagine a exploding series of "1's"!

Good stuff