diff --git a/code/modules/atmospherics/gasmixtures/gas_mixture.dm b/code/modules/atmospherics/gasmixtures/gas_mixture.dm
index 44412a1a6f5..b0fb6f8cb68 100644
--- a/code/modules/atmospherics/gasmixtures/gas_mixture.dm
+++ b/code/modules/atmospherics/gasmixtures/gas_mixture.dm
@@ -373,8 +373,8 @@ GLOBAL_LIST_INIT(gaslist_cache, init_gaslist_cache())
 			sharer_temperature = max(sharer_temperature + heat/sharer_heat_capacity, TCMB)
 			if(sharer)
 				sharer.temperature = sharer_temperature
-				if (initial(sharer.gc_share)) 
-					sharer.garbage_collect() 
+				if (initial(sharer.gc_share))
+					sharer.garbage_collect()
 	return sharer_temperature
 	//thermal energy of the system (self and sharer) is unchanged
 
@@ -410,8 +410,9 @@ GLOBAL_LIST_INIT(gaslist_cache, init_gaslist_cache())
 	if(!length(cached_gases))
 		return
 	var/list/reactions = list()
-	for(var/I in cached_gases)
-		reactions += SSair.gas_reactions[I]
+	for(var/datum/gas_reaction/G in SSair.gas_reactions)
+		if(cached_gases[G.major_gas])
+			reactions += G
 	if(!length(reactions))
 		return
 	reaction_results = new
diff --git a/code/modules/atmospherics/gasmixtures/reactions.dm b/code/modules/atmospherics/gasmixtures/reactions.dm
index 43c9cd95735..185bddc9524 100644
--- a/code/modules/atmospherics/gasmixtures/reactions.dm
+++ b/code/modules/atmospherics/gasmixtures/reactions.dm
@@ -2,8 +2,6 @@
 
 /proc/init_gas_reactions()
 	. = list()
-	for(var/type in subtypesof(/datum/gas))
-		.[type] = list()
 
 	for(var/r in subtypesof(/datum/gas_reaction))
 		var/datum/gas_reaction/reaction = r
@@ -16,26 +14,18 @@
 				var/datum/gas/req_gas = req
 				if (!reaction_key || initial(reaction_key.rarity) > initial(req_gas.rarity))
 					reaction_key = req_gas
-		.[reaction_key] += list(reaction)
-		sortTim(., /proc/cmp_gas_reactions, TRUE)
+		reaction.major_gas = reaction_key
+		. += reaction
+	sortTim(., /proc/cmp_gas_reaction)
 
-/proc/cmp_gas_reactions(list/datum/gas_reaction/a, list/datum/gas_reaction/b) // compares lists of reactions by the maximum priority contained within the list
-	if (!length(a) || !length(b))
-		return length(b) - length(a)
-	var/maxa
-	var/maxb
-	for (var/datum/gas_reaction/R in a)
-		if (R.priority > maxa)
-			maxa = R.priority
-	for (var/datum/gas_reaction/R in b)
-		if (R.priority > maxb)
-			maxb = R.priority
-	return maxb - maxa
+/proc/cmp_gas_reaction(datum/gas_reaction/a, datum/gas_reaction/b) // compares lists of reactions by the maximum priority contained within the list
+	return b.priority - a.priority
 
 /datum/gas_reaction
 	//regarding the requirements lists: the minimum or maximum requirements must be non-zero.
 	//when in doubt, use MINIMUM_MOLE_COUNT.
 	var/list/min_requirements
+	var/major_gas //the highest rarity gas used in the reaction.
 	var/exclude = FALSE //do it this way to allow for addition/removal of reactions midmatch in the future
 	var/priority = 100 //lower numbers are checked/react later than higher numbers. if two reactions have the same priority they may happen in either order
 	var/name = "reaction"