Gas mask filters Plasma and N2O.

code/modules/clothing/clothing.dm

@@ -1,6 +1,7 @@
 /obj/item/clothing
 	name = "clothing"
 	var/list/species_restricted = null //Only these species can wear this kit.
+	var/gas_filter_strength = 0			//For gas mask filters
 
 //BS12: Species-restricted clothing check.
 /obj/item/clothing/mob_can_equip(M as mob, slot)

code/modules/clothing/masks/gasmask.dm

@@ -1,6 +1,6 @@
 /obj/item/clothing/mask/gas
 	name = "gas mask"
-	desc = "A face-covering mask that can be connected to an air supply."
+	desc = "A face-covering mask that can be connected to an air supply. Filters harmful gases from the air."
 	icon_state = "gas_alt"
 	flags = FPRINT | TABLEPASS | MASKCOVERSMOUTH | MASKCOVERSEYES | BLOCK_GAS_SMOKE_EFFECT | MASKINTERNALS
 	flags_inv = HIDEEARS|HIDEEYES|HIDEFACE
@@ -9,6 +9,7 @@
 	gas_transfer_coefficient = 0.01
 	permeability_coefficient = 0.01
 	siemens_coefficient = 0.9
+	gas_filter_strength = 1
 
 //Plague Dr suit can be found in clothing/suits/bio.dm
 /obj/item/clothing/mask/gas/plaguedoctor

code/modules/mob/living/carbon/human/life.dm

@@ -97,7 +97,7 @@
 
 		handle_pain()
 
-		handle_medical_side_effects()
+//		handle_medical_side_effects()
 
 	handle_stasis_bag()
 
@@ -322,14 +322,7 @@
 						// Not enough air around, take a percentage of what's there to model this properly
 					breath_moles = environment.total_moles()*BREATH_PERCENTAGE
 
-					breath = loc.remove_air(breath_moles)
-
-					if(!is_lung_ruptured())
-						if(!breath || breath.total_moles < BREATH_MOLES / 5 || breath.total_moles > BREATH_MOLES * 5)
-							if(prob(5))
-								rupture_lung()
-
-					// Handle chem smoke effect  -- Doohl
+					// Handle filtering
 					var/block = 0
 					if(wear_mask)
 						if(wear_mask.flags & BLOCK_GAS_SMOKE_EFFECT)
@@ -341,6 +334,16 @@
 						if(head.flags & BLOCK_GAS_SMOKE_EFFECT)
 							block = 1
 
+					if(!block && !wear_mask)
+						breath = loc.remove_air(breath_moles, 0)
+					else
+						breath = loc.remove_air(breath_moles, wear_mask.gas_filter_strength) //Filters out harmful gases
+
+					if(!is_lung_ruptured())
+						if(!breath || breath.total_moles < BREATH_MOLES / 5 || breath.total_moles > BREATH_MOLES * 5)
+							if(prob(5))
+								rupture_lung()
+
 					if(!block)
 
 						for(var/obj/effect/effect/chem_smoke/smoke in view(1, src))

code/modules/mob/living/carbon/monkey/life.dm

@@ -225,7 +225,6 @@
 					breath = location_as_object.handle_internal_lifeform(src, BREATH_VOLUME)
 				else if(istype(loc, /turf/))
 					var/breath_moles = environment.total_moles()*BREATH_PERCENTAGE
-					breath = loc.remove_air(breath_moles)
 
 					// Handle chem smoke effect  -- Doohl
 					var/block = 0
@@ -233,6 +232,11 @@
 						if(istype(wear_mask, /obj/item/clothing/mask/gas))
 							block = 1
 
+					if(!block)
+						breath = loc.remove_air(breath_moles, 0)
+					else
+						breath = loc.remove_air(breath_moles, wear_mask.gas_filter_strength) //Filters out harmful gases
+
 					if(!block)
 
 						for(var/obj/effect/effect/chem_smoke/smoke in view(1, src))

code/modules/mob/living/living.dm

@@ -262,6 +262,7 @@
 	blinded = 0
 	eye_blind = 0
 	eye_blurry = 0
+	eye_stat = 0
 	ear_deaf = 0
 	ear_damage = 0
 	heal_overall_damage(1000, 1000)