Fun little story though first.
As you know the fort is in an evil jungle with periodic wicked soot clouds that roll in and turn living things into horrible killing machines. For this reason we keep everyone burrowed inside, except for when we go tree harvesting which is very rare and I keep a super close eye on things. It still catches the odd caravan with a cloud or one of the pack animals will step on some of the residue that says "pile of wicked soot". I've stopped cleaning up the messes because it's just too time consuming, and I don't want to risk one of the children changing a sock and then stepping into residue while the cleanup is going on.
So anyways a few years back a caravan gets clouded and kills itself, no big deal. A few dwarf months later a craftsdwarf in the fort turns into a wicked soot husk and has to be killed. Weird thing was, he was way down below in the hell fort, there was no way he could have stepped in anything. Sometimes the weapons will get coated in wicked soot, but it's usually no problem as everyone is in a sqaud and wears armor even if they are not on duty, so gauntlets and boots always prevent any contamination. So I chalked it up to a weird random chance. A few days later another dwarf turns into a wicked soot husk inside the fortress in hell. At this point I'm determined to figure out what is happening so I scour every square of the fortress for residue and I can't find anything. I check all their belongings, all the workshops, still nothing. I've had the game paused for hours looking into it and now it is starting to make my brain hurt. They aren't touching any residue, even if they were they are fully clothed, and they aren't coming anywhere near any clouds, so what could be turning them?
Finally, I spot a pattern. Next to where both of them turned, a seed was on the ground not far away. After looking at them, I found them both to be squash seeds. That's weird because we only farm underground, in hell, so squashes shouldn't exist. At this point I start connecting the dots and remembered the last caravan that died. A small pile of food had made it's way into the fort within the burrow before the carrier was killed, so the dwarves in the fort grabbed it and stored it. Squashes. So I look them up in the stocks menu and sure enough there's a coating of wicked soot on them. The soot was getting past the armor because the dwarves were eating it. So next I zoom to where all the squashes are, and my jaw dropped. At least half the dwarves had a squash in their backpack as "provisions" because they were all in squads. They were all ticking time bombs waiting to go off whenever they got hungry. So, eventually to solve the problem I had take them all out of military service to get them to drop their provisions and backpack and then forbid all of the contaminated squashes.
Just goes to show this game still has some tricks up it's sleeve.