I think you have just now exposed the worst trap possible for a lower level party.
"Hey, I'm going to put an Acid Fog trap in, dealing 2d6 points of damage to all creatures and objects within the vicinity! Now you're all going to be naked and have no provisions! And be highly burned and almost dead! Have fun!"
In short? The party's equipment and provisions would all be destroyed and despoiled, and if the party isn't already dead that round, they will be in the next.
Worst. Trap. Ever.
Acid Flasks do not have their stopper dissolve when you hold them upside down, so potions should probably be save. But apart from that, every object would be affected; you'll end up having to assign hitpoints to every item in the PCs' possession. That's a lot of work. Why not just make a Disintegrate trap? It's the same spell level. And it'll probably cause the same sort of player revolt.
It's a Conjuration, the attack isn't magical and so the rules for magical attacks do not apply.
The spell creates the Acid Fog. The Acid Fog then does the (mundane) damage "to each creature and object within it".
Nope. Unless you hit with a torch fog. Ever walked through a fog? Everything gets wet. Every Thing.
As "unrealistic" as it is, sometimes realism has to bow out to making a game be playable. I have been coming to terms with this myself slowly... the game is a little cartoony if you think to hard about it. Its not just acid fog, but any fireball or burning hands spell should really burn off everyone's clothes, leaving a bunch of naked PCs who don't use metal armor... but that's not how the game works.
One way to cope might be to consider that all creatures in the deity infested fantasy setting are pieces of a massive chess game played by deities, so even non-magical beings have some degree of supernatural protection offered to them and their bodies, even if they are atheists, because all physical manifestations in the world are actually coalesced from divine will.
If you are "strong" you are part of the portfolio of all deities who are strong, even ones you don't serve, because you further their ends. I know this is the rules forum, and this is going off topic, but it might help to frame how you should approach rules... don't over-use real world logic when there is something in the RAW that already defines what to do in a given situation to keep the game playable... and add flavor to it like the above if it helps make it more fun.
I agree that having "clothes and equipment burn off" is quite funny from an objective perspective:
The Party walks into the room, the burning stench of fecal matter pervades the dewy, weed-infested walls. In a matter of seconds, a large portion of their equipment and supplies begin to dwindle, coughing from the apparently destructive gas that fumes from the door's opening; the female wizard covering herself with what little garments survive the powerful, the cleric turning red as he is inadvertantly sinning in front of his entire group, the rogue crying over most of his earning turning to mere dust, and the big dumb barbarian feeling a minor breeze toward the lower waist.
Many glares are given toward the big dumb barbarian, the party fearing he had one too many of those insane spicy wine drinks he tries concocting, believing it was him who made such a nasty odor (that is, one that is more nasty than what he usually gives to the senses). Of course, the big dumb barbarian does what he does best, which is play big and dumb about it.
Again, comical.
But from the player's perspective?
"Just great; my super awesome Keen Greatsword +2 is considered Broken, the wizard's Bound Object (Spellbook) is disintegrated, losing so many of his special powers, the Cleric has no armor to help the Barbarian out on the front lines, and now our Rogue is crying because all of our gold got vaporized by some stupid green cloud of doom and sadness.
This DM has got to be the biggest dick in the entire world to torture us like this. What's next, he going to throw a Red Dragon at us?"
I can totally see PC's acting like this, assuming you take the RAW description as it is. And are you sure it's wise to be throwing a 6th level spell against 6th level characters?
Even if it does harm objects, bear in mind that energy damaged is halved before hardness.
I'm also tossing my hat in with it dealing damage to everything in the area, it's how we've always run it in our games. A similar trap almost took out our party of epic level characters (large room, slowed movement, magically sealed/locked door, LOTS of Heals spells used), it was vicious so keep that in mind. If you are worried about precious magical items being destroyed you can rule hardness comes into effect (as it is "real" and the spell doesn't say anything about bypassing hardness). Metal items will fare better obviously, but even non metallic weapons/items should be a bit more safe unless you roll high repeatedly.
My understanding of RAW is the same as Setzer9999's. Without a 1 on a saving throw it is not possible to damage attended objects with a spell unless the spell specifically calls out attended objects. This spell does not.
Now with that aside lets look at what happens during gameplay IF this spell were allowed to hit all of the PCs equipment:
You hit the PCs with this trap. Now for the next hour the players are going over each and every peice of equipment. The players are looking up all of the hardnesses and hitpoints for all of that equipment. After the damage is assigned you spend another 30minutes trying to repair it all and those things that were outright destroyed you have to figure out how to deal with that.
One trap: 90minutes worth of 'how many hitpoints does a pair of boots have?'
It is just not worth it. Attended objects do not take damage unless the spell states they do.
- Gauss
My understanding of RAW is the same as Setzer9999's. Without a 1 on a saving throw it is not possible to damage attended objects with a spell unless the spell specifically calls out attended objects. This spell does not.
Now with that aside lets look at what happens during gameplay IF this spell were allowed to hit all of the PCs equipment:
You hit the PCs with this trap. Now for the next hour the players are going over each and every peice of equipment. The players are looking up all of the hardnesses and hitpoints for all of that equipment. After the damage is assigned you spend another 30minutes trying to repair it all and those things that were outright destroyed you have to figure out how to deal with that.
One trap: 90minutes worth of 'how many hitpoints does a pair of boots have?'
It is just not worth it. Attended objects do not take damage unless the spell states they do.
- Gauss
I think your being generous with your timetable Gauss... lol. RAW or RAI or whatever... this would be a nightmare if ruled this way. In any game I played in or run it would take the rest of the night to clear up what got destroyed and what lasted. We usually have very detailed list of what our characters have(read: long list).
Attended objects should be fine unless the player rolls a one. At least then you would only have one unlucky players figuring it out instead of a game halting nightmare.