One last ashwalker fix

code/modules/atmospherics/auxgm/breathing_classes.dm

@@ -14,6 +14,12 @@
 	var/high_alert_category = "too_much_oxy"
 	var/high_alert_datum =  /atom/movable/screen/alert/too_much_oxy
 
+/datum/breathing_class/proc/get_effective_pp(datum/gas_mixture/breath)
+	var/mol = 0
+	for(var/gas in gases)
+		mol += breath.get_moles(gas) * gases[gas]
+	return (mol/breath.total_moles()) * breath.return_pressure()
+
 /datum/breathing_class/oxygen
 	gases = list(
 		GAS_O2 = 1,

code/modules/surgery/organs/lungs.dm

@@ -528,7 +528,8 @@
 		BZ_brain_damage_min += bz
 
 	gas_max[GAS_N2] = PP(breath, GAS_N2) + 5
-	var/o2_pp = PP(breath, GAS_O2)
+	var/datum/breathing_class/class = GLOB.gas_data.breathing_classes[breathing_class]
+	var/o2_pp = class.get_effective_pp(breath)
 	safe_breath_min = 0.3 * o2_pp
 	safe_breath_max = 1.3 * o2_pp
 	..()