What does "sound_effect" "fire" "ignition" actually hook into? (0.F-3)

Game Talk The Toolbox
1

This is for 0.F-3 Stable, using @'s Soundpack.
I’ve been changing and adding a few sound effects in the pack and wanted to change this one also.
I had assumed it mapped to the ‘Start a fire (quickly)’ action but apparently not. It also doesn’t trigger when fire spreads to an adjacent tile.
The sound files I’m using work fine, as tested by mapping them to “misc” “whistle”. The relevant section in the JSON looks like this:

{
        "type": "sound_effect",
        "id" : "fire",
        "variant" : "ignition",
        "volume" : 90,
        "files" : [
            "effects/misc/light_fire01.ogg",
            "effects/misc/light_fire02.ogg"
        ]
    },

I’ve searched for “sfx::” lines in several source code files that seemed likely candidates but can’t find any mention of this specific trigger. That said, I am not a programmer and may have gone about this the wrong way.
So my question is: Which action or event does “fire” “ignition” actually hook into?

(Also, if I may, is “misc” “cough” a game-wide effect or is it player-specific? I ask because there don’t seem to be m | f variants as there are with other sfx. By the way, it’s listed as “misc” “coughing” in the Soundpacks.md documentation, but @'s uses “cough” and it seems to work?)