Booby trap flour explosion

[Pursuivant]

Originally Posted by Anaraxes

Air College mages could do the same thing, without being restricted to using only grain dust and alcohol.

True. It also occurs to me that the Food college is the wrong place for a dust explosion spell. It should be in the Technology (Energy) College. At TL3 and below you can only create flour or wood dust explosions. At TL4, you get coal dust. At TL5+, you get proper FAE effects. Of course, functionally, it's the same as a purely magical Fire college spell.

An Air College mage could use a number of spells to get flammable dust, etc. into suspension and keep it there, but a dedicated Tech spell would produce a reliable blast. Technomancer-style military enchanters could create MOAB-style munitions which are small enough to mount on fighter jets rather than requiring a cargo plane or bomber.

[Donny Brook]

I'm planning the room trap to look like a normal disused institutional kitchen with flour scattered around, apparently from a large busted open bag of flour coincidentally laying under a large fan-hood. Total weight of flour will be about double the needed LFL for the space. Triggering the trap turns the fan on. Alert players will be warned by the fact the fan blows very strongly and inward rather than evacuating. Two or three seconds later ignition will occur. I've settled on a reduced REF of 1 to account for imperfect dispersion.

[Fred Brackin]

Originally Posted by Pursuivant

. At TL3 and below you can only create flour or wood dust explosions. r.

There's also finely ground charcoal (i.e. the "fuel" segment of black powder).

It occurs to me to wonder if mixing sulfur dust in with your powdered charcoal might not let the sulfur acts a s a catalyst as it does in black powder.

[Anthony]

Originally Posted by Fred Brackin

It occurs to me to wonder if mixing sulfur dust in with your powdered charcoal might not let the sulfur acts a s a catalyst as it does in black powder.

It's not a catalyst, it's a fuel (catalysts are not consumed).

In general the problem for fuel-air explosives is that you're limited by the oxygen content of air, which is about 0.25 kg/m^3 or 0.42 lb/cubic yard, and you need about 3x as much oxygen as fuel; thus, if you want a substantial explosion, you need to disperse your fuel over an extremely large volume. Adding your own oxidizer lets you have a larger explosion in a given volume and increases the explosive range, but also adds a lot of weight and quickly turns into "why not just fill the trap with gunpowder and forget about the complexities of a fuel-air explosive".

[The Colonel]

Also, if it helps, dust explosions tend to catenate - you'll get one blast, that stirs up dust cloud for the next one, potentially increasing in size each time - the Bosley Mill explosions in 2015 were a "good" example.

[RGTraynor]

Originally Posted by Anthony

Adding your own oxidizer lets you have a larger explosion in a given volume and increases the explosive range, but also adds a lot of weight and quickly turns into "why not just fill the trap with gunpowder and forget about the complexities of a fuel-air explosive".

Eh, or just have a dozen crossbowmen to hand with instructions to whack interlopers in the head ...

[Pursuivant]

Originally Posted by Donny Brook

Alert players will be warned by the fact the fan blows very strongly and inward rather than evacuating. Two or three seconds later ignition will occur. I've settled on a reduced REF of 1 to account for imperfect dispersion.

REF 1 might be a bit too generous. 0.9 or less might be more like it.

It's also one of those traps where Traps skill should get a healthy bonus for complementary skills like PS (Firefighter, Miller or Miner). If any of the PCs has Explosives or Hazardous Materials (Chemical) skill, it should be able to substitute for the usual Traps skill to recognize the danger.

If you want to be really vicious, have the explosion bring the roof down or otherwise crush or trap victims. The big killers in a building explosion aren't so much the explosion itself as the resulting structural collapse and fire.

[Anthony]

The other issue with flour explosions is that they really come under the category of "safety hazards", not "weapons". There's a big difference between "explodes often enough that you should take safety measures to prevent it" and "explodes often enough to be useful as a weapon".

[Varyon]

Originally Posted by Pursuivant

REF 1 might be a bit too generous. 0.9 or less might be more like it.

Given the GURPS damage scales with the square root of REF, 0.9 isn't really substantially different enough from 1 to worry about (it's right around 95% of the damage). Lower can be, of course; your previous suggestion of 0.5+(1d*0.1) would probably work out alright, ranging from ~75% to ~105% of REF 1's damage. But if OP doesn't want to bother with that, REF 1 is probably fine.

Originally Posted by Anthony

The other issue with flour explosions is that they really come under the category of "safety hazards", not "weapons". There's a big difference between "explodes often enough that you should take safety measures to prevent it" and "explodes often enough to be useful as a weapon".

Of course, how much that matters depends heavily on how cinematic your campaign is - or, potentially, how fantastical it is (the thread I linked earlier had a wind-controlling Djinn suspending the flour in the air at the direction of a mage using IIRC the Calculation spell to work out the optimal mixture for a detonation). A fume hood running in reverse implies fantastical probably isn't on the table, but the setting may well still be a rather cinematic one.

[Donny Brook]

Something I'm just now wondering about -- how do you handle concussive damage for targets that are inside the origination envelope of the blast?