Update: Experiments with SoF proove to be more difficult than with Frog Demons due to the SoF innate ability to burn to nothing wooden cages set up in cage traps simply by standing one or two tiles away. I will try again after forging many steel cages. Interestingly, placing barrels of booze on top of the section of floor set to come crashing down will result in the fabled booze bomb when it hits the SoF. At least molten dwarven wine and long land beer flew all over the place (causing no harm to the SoF).
That's because the booze bomb is (despite my best efforts) a myth that just won't die.
The booze boils, the steam from it happens to be red and thus look like an explosion, even though it is harmless (like steam). Any injuries from the 'booze bomb' are either caused by whatever lit the thing on fire in the first place, or the burning barrel (I'm fairly sure the heat from the burning barrel can injure creatures standing next to it, not just on top of it). Spirits of fire don't take damage from heat (at least plain old wood fire level heat) so they are uninjured.
As for the spirit of fire falling into the chasm, AFAIK this is a known bug - fliers will sometimes just decide to not fly anymore, and if they are over a chasm they fall in and die. If you modded your dwarves to fly in the 2d version that would happen from time to time, which was kind of funny.