The following series of experiments were performed in order to determine if a burning creature could set a stockpile of booze on fire, and to determine what effect a burning barrel of booze would have on nearby objects. In particular, I wanted to determine if a burning booze barrel would set adjacent barrels on fire, leading to a chain reaction which would destroy the entire stockpile.
Experiment #1: Setting an elf on fire.
For the first part of the experiment, I captured a large number of elves during an elven siege. (This game was played in a modded world where the elven civilization has diplomats, making it easy to trigger war with them at will). These elves were not stripped of their flammable wooden gear before the test.
I build a device similar to the standard mist generation system, with four pumps to rapidly circulate a single tile of magma through four different locations. A pressure plate linked to two floor hatches was used to force the experimental subject to stand in a specific location, where they would be periodically exposed to magma by the sprayer. I had an unlockable door leading to a stockpile of booze, with the intent that the elf, once set on fire, would be released to run through the room full of booze.
The results:
The experiment was repeated with half a dozen elves. None of the elves or their equipment caught on fire while the elf was still alive. On exposure to magma the elves would instead melt, then die, and only then would the corpse and dropped gear catch on fire.
I am considering other methods for making an elf catch on fire while still being alive for long enough to run through a room full of booze. Traps have been set out around the magma pipe in hopes of catching a fire imp.
As such, the first experiment can't be considered a full success, but I still have to count any experiment involving setting elves on fire as a partial success anyway.
Experiment #2: Burning Booze.
A small stockpile was created, five tiles long. The stockpile was set to only accept alcohol. One of the squares of the tile was located under part of the magma pumping system, permitting a single barrel to be selectively exposed to magma. Once the stockpile was full, the door was locked and the magma pumps switched on.
The results:
Fairly soon after the magma pump was started, the booze in the boiled, creating a cloud of boiling alcohol around the barrel. This did not seem to cause any harm to any of the adjacent barrels. At this stage, the barrel itself was undamaged.
After the alcohol had all boiled, the barrel caught on fire. The stockpile filled with smoke, but no damage was observed to the adjacent barrel.
Once the barrel had completely burned away and the smoke cleared, the only barrel that had been damaged had been the one directly exposed to magma.
Conclusion: it does not appear that fire spreads from barrel to barrel in a booze stockpile. Only those barrels directly set on fire are destroyed. Booze in a burning barrel boils away without causing any apparent damage to adjacent barrels. The effect of boiling booze on nearby creatures has not yet been tested.
I expect that a burning creature can set barrels on fire, but I have yet to manage to test this. I will need a way to reliably set an elf on fire without killing it first.