Dust Explosion - Grain, flour, wheat

[Icelander]

Originally Posted by Anders

Won't the djinni be SOL?

Summoned creature that is a sophisticated copy of a real one, but doesn't really live or die in a conventional sense. His existence lasts up to 15 minutes on the Prime Material Plane. It doesn't matter to the real djinni whose form and powers some mysterious planar powers borrowed to make a simulacrum to answer a summoning spell whether that simulacrum suffers a critical existence failure from being in a BOOM, if the spell is dispelled or if it just runs its course.

[Anaraxes]

Originally Posted by Nereidalbel

I got my value for TNT equivalence with this calculator

Thanks. I guess the numbers I found weren't so far off after all. But then, there's a reason special forces don't just carry bags of flour with them instead of C4, so (as Anthony said) there has to be more to rating an explosive than just heat of combustion. Perhaps too much detail for this question, though.

Originally Posted by Anders

Won't the djinni be SOL?

The dust won't immediately hit the ground once the djinn stops stirring the pot. A kind mage might let the djinn fly up and away, and only then ignite the explosion. But then, Icelander says that it's disposable, so I'd guess the PCs wouldn't risk the effort to coordinate, and would just sacrifice the elemental.

[Nereidalbel]

Originally Posted by Anaraxes

Thanks. I guess the numbers I found weren't so far off after all. But then, there's a reason special forces don't just carry bags of flour with them instead of C4, so (as Anthony said) there has to be more to rating an explosive than just heat of combustion. Perhaps too much detail for this question, though.

The dust won't immediately hit the ground once the djinn stops stirring the pot. A kind mage might let the djinn fly up and away, and only then ignite the explosion. But then, Icelander says that it's disposable, so I'd guess the PCs wouldn't risk the effort to coordinate, and would just sacrifice the elemental.

C4 explodes when you want it to. Flour does not cooperate well, and requires more volume for the same boom.

[Icelander]

Originally Posted by Anaraxes

The dust won't immediately hit the ground once the djinn stops stirring the pot. A kind mage might let the djinn fly up and away, and only then ignite the explosion. But then, Icelander says that it's disposable, so I'd guess the PCs wouldn't risk the effort to coordinate, and would just sacrifice the elemental.

Given the importance of getting the mix even close to right and the immense influence that a magical, elemental being of air can have on it, given that it can take on a form of a 60' tall whirlwind with a base 30' in diameter and has pretty good control over its body and the stuff it picks up in even in wind form, it's worthwhile to 'sacrifice' the summoned being to ensure a few extra seconds of manipulating conditions within the dust cloud.

Given a quiet environment and constant guidance by the PC using Measurement spells to monitor the dust-to-air ratio of the cloud, the djinni could easily ensure near-perfect conditions for a massive dust conflagration, if not explosion.* It would take him several minutes of uninterrupted work, though. He'd have to stir up all the dust and then use Control Air carefully around himself, responding to data gathered from Measurement spells for individual hexes, working on small parts of the cloud only in each individual second.

As it is, though, he'll most probably have from 20-30 seconds after the bags hit the ground. It might stretch up to a minute, but it's unreasonable to expect that organising and dispatching an effective response of heroes, priest and magicians to a rampaging djinni to take much more than that. It's very probable that the djinni will already be destroyed by the time the PC launches his fire bombing on the cloud.

*The dust cloud is not in a confined space, so even a perfect ratio will result in a more of a huge WHOOSH followed by an implosive CLAP than a huge shockwavy BOOM.

[acrosome]

I apologize- I only read about half the thread. But, if you're mages can haul "a ton or two" into the sky is there a reason you're not using a ton or two of low-TL napalm? Which would then be handily ignited by your fireballs?

See this discussion- even a 500 pound payload is fracking terrifying.

Fire terrifies packed ranks of men. At the very least you will wreak havoc with their unit cohesion.

Also, probably easier than trying to engineer a low-TL FAE.

[Nereidalbel]

Originally Posted by acrosome

I apologize- I only read about half the thread. But, if you're mages can haul "a ton or two" into the sky is there a reason you're not using a ton or two of low-TL napalm? Which would then be handily ignited by your fireballs?

See this discussion- even a 500 pound payload is fracking terrifying.

Fire terrifies packed ranks of men. At the very least you will wreak havoc with their unit cohesion.

Also, probably easier than trying to engineer a low-TL FAE.

They have less than a day of prep time, so, they have to use what's on hand.

[Nereidalbel]

Here, have some more data! Minimum dust/air ratios needed for a boom, as well as ignition temperatures required. Spoiler alert: your fireball wands have this covered.

If somebody can summon a couple very low-level air elementals, you may just be able to introduce enough oxygen to get a small mushroom cloud out of this.

[Icelander]

Originally Posted by Nereidalbel

Here, have some more data! Minimum dust/air ratios needed for a boom, as well as ignition temperatures required. Spoiler alert: your fireball wands have this covered.

Grain dust and corn starch seem the closest to flour, there. There's a lot of difference in the minimum concentration between those, however.

Anecdotally, finely ground flour is supposed to be very dangerous, as potentially explosive dust goes. Would 30-50 grams per cubic meter be a reasonable minimum concentration for the most finely ground flour that can be found among a grain supply in the thousands of tons, probably looted from several bakeries specialising in desserts and delicacies for the officer aristocracy with the occupying army?

Originally Posted by Nereidalbel

If somebody can summon a couple very low-level air elementals, you may just be able to introduce enough oxygen to get a small mushroom cloud out of this.

Good idea. Only one mage that is not otherwise assigned has the power to summon an elemental of any size, but as it happens, there are four summoning wands available to the PC and his men. Anyone with Magery can use them.

Those can be used to summon 4' diameter air elementals for 5 minutes per casting, with each wand having 5-50 charges. And the elementals can take a whirlwind form similar to the djinni, if smaller and less powerful. It takes 10 seconds to perform each summoning, but that will still mean at least 4 small air elementals and maybe 8 or 12 if the enemy is slow to respond.

[Anthony]

Originally Posted by Icelander

Would 30-50 grams per cubic meter be a reasonable minimum concentration

The problem is that safe concentrations are generally "below this density it will never explode", not "above this density it will always explode". 50g/m^3 is otherwise reasonable for flour.

[cptbutton]

Originally Posted by Anthony

The problem is that safe concentrations are generally "below this density it will never explode", not "above this density it will always explode". 50g/m^3 is otherwise reasonable for flour.

Yes, we need to remember this sort of thing is primarily of interest to safety engineers, not weapons designers, who have rather different standards. A 1% chance of exploding is far too high for the former and far too low for the latter.