code/modules/atmospherics/environmental/LINDA_fire.dm

/proc/init_hotspot_reactions	Returns reactions which will contribute to a hotspot's size.
/obj/effect/hotspot	Hotspot objects interfaces with the temperature of turf gasmixtures while also providing visual effects. One important thing to note about hotspots are that they can roughly be divided into two categories based on the bypassing variable.
/datum/hot_group	handle the grouping of hotspot and then determining an average center to play sound in