Fixes issues:

#2632 Fire Issues (Fire doors work, Flamethrower reverted to making a flamethrower liquid fuel subtype, flame grenades now make a puddle of welder fuel that is lit aflame with napalm)
#2630 (The code has been calling (turf).temperature_expose when it was supposed to be hotspot_expose), #1865 (aqain)(Added a check to remove trace gas fuel under a certain point).
Also: added a flashpoint value for plasma, which is the temperature at which it self-ignites (Currently 246C or 519K which is equal to gasoline)
Partial-tile firedoors now default to full-tile firedoors as the part-tile ones were breaking ZAS zones entirely.  Possible cause of #2627 and maybe #2451, but those need tested and I did not have time.

code/ZAS/Fire.dm

@@ -84,11 +84,11 @@ obj
 				var/turf/simulated/floor/S = loc
 				if(!S.zone) del src //Cannot exist where zones are broken.
 
-				if(istype(S,/turf/simulated/floor))
+				if(istype(S))
 					var
 						datum/gas_mixture/air_contents = S.return_air()
 						//Get whatever trace fuels are in the area
-						datum/gas/volatile_fuel/fuel = locate(/datum/gas/volatile_fuel/) in air_contents.trace_gases
+						datum/gas/volatile_fuel/fuel = locate() in air_contents.trace_gases
 						//Also get liquid fuels on the ground.
 						obj/effect/decal/cleanable/liquid_fuel/liquid = locate() in S
 
@@ -115,7 +115,7 @@ obj
 
 									//Spread the fire.
 									if(!(locate(/obj/fire) in enemy_tile))
-										if( prob( firelevel*10 ) )
+										if( prob( firelevel*10 ) && S.CanPass(null, enemy_tile, 0,0) && enemy_tile.CanPass(null, S, 0,0))
 											new/obj/fire(enemy_tile,firelevel)
 
 					if(flow)
@@ -136,6 +136,8 @@ obj
 
 							//Burn the gas mixture.
 							flow.zburn(liquid)
+							if(fuel && fuel.moles <= 0.00001)
+								del fuel
 
 						else
 
@@ -160,14 +162,12 @@ obj
 		New(newLoc,fl)
 			..()
 
-			if(!istype(loc, /turf) || !loc.CanPass(null, loc, 0, 0))
+			if(!istype(loc, /turf))
 				del src
 
 			dir = pick(cardinal)
 			//sd_SetLuminosity(3,2,0)
 			firelevel = fl
-			for(var/mob/living/carbon/human/M in loc)
-				M.FireBurn(min(max(0.1,firelevel / 20),10)) //Burn the humans!
 			air_master.active_hotspots.Add(src)
 
 		Del()
@@ -195,12 +195,8 @@ datum/gas_mixture/proc/zburn(obj/effect/decal/cleanable/liquid_fuel/liquid)
 
 		if(fuel)
 		//Volatile Fuel
-			if(fuel.moles < 0.01)
-				trace_gases.Remove(fuel)
-				fuel = null
-			else
-				total_fuel += fuel.moles
-				fuel_sources++
+			total_fuel += fuel.moles
+			fuel_sources++
 
 		if(liquid)
 		//Liquid Fuel

code/ZAS/ZAS_Zones.dm

@@ -200,7 +200,7 @@ zone/proc/process()
 	progress = "problem with an inbuilt byond function: some conditional checks"
 
 	//Only run through the individual turfs if there's reason to.
-	if(air.graphic != air.graphic_archived || air.temperature > FIRE_MINIMUM_TEMPERATURE_TO_EXIST)
+	if(air.graphic != air.graphic_archived || air.temperature > PLASMA_FLASHPOINT)
 
 		progress = "problem with: turf/simulated/update_visuals()"
 
@@ -215,10 +215,10 @@ zone/proc/process()
 			progress = "problem with: item or turf temperature_expose()"
 
 			//Expose stuff to extreme heat.
-			if(air.temperature > FIRE_MINIMUM_TEMPERATURE_TO_EXIST)
+			if(air.temperature > PLASMA_FLASHPOINT)
 				for(var/atom/movable/item in S)
 					item.temperature_expose(air, air.temperature, CELL_VOLUME)
-				S.temperature_expose(air, air.temperature, CELL_VOLUME)
+				S.hotspot_expose(air, air.temperature, CELL_VOLUME)
 
 	progress = "problem with: calculating air graphic"
 

code/game/machinery/doors/firedoor.dm

@@ -223,6 +223,8 @@
 
 
 /obj/machinery/door/firedoor/border_only
+//These are playing merry hell on ZAS.  Sorry fellas :(
+/*
 	icon = 'icons/obj/doors/edge_Doorfire.dmi'
 	glass = 1 //There is a glass window so you can see through the door
 			  //This is needed due to BYOND limitations in controlling visibility
@@ -257,3 +259,4 @@
 		if(istype(source)) air_master.tiles_to_update += source
 		if(istype(destination)) air_master.tiles_to_update += destination
 		return 1
+*/

code/game/objects/items/weapons/flamethrower.dm

@@ -209,15 +209,17 @@
 /obj/item/weapon/flamethrower/proc/ignite_turf(turf/target)
 	//TODO: DEFERRED Consider checking to make sure tank pressure is high enough before doing this...
 	//Transfer 5% of current tank air contents to turf
-	var/datum/gas_mixture/air_transfer = ptank.air_contents.remove_ratio(0.05)
-	air_transfer.toxins = air_transfer.toxins * 5 // This is me not comprehending the air system. I realize this is retarded and I could probably make it work without fucking it up like this, but there you have it. -- TLE
+	var/datum/gas_mixture/air_transfer = ptank.air_contents.remove_ratio(0.02*(throw_amount/100))
+	//air_transfer.toxins = air_transfer.toxins * 5 // This is me not comprehending the air system. I realize this is retarded and I could probably make it work without fucking it up like this, but there you have it. -- TLE
+	new/obj/effect/decal/cleanable/liquid_fuel/flamethrower_fuel(target,air_transfer.toxins,get_dir(loc,target))
+	air_transfer.toxins = 0
 	target.assume_air(air_transfer)
 	//Burn it based on transfered gas
+	//target.hotspot_expose(part4.air_contents.temperature*2,300)
 	target.hotspot_expose((ptank.air_contents.temperature*2) + 380,500) // -- More of my "how do I shot fire?" dickery. -- TLE
 	//location.hotspot_expose(1000,500,1)
 	return
 
-
 /obj/item/weapon/flamethrower/full/New(var/loc)
 	..()
 	weldtool = new /obj/item/weapon/weldingtool(src)

code/game/objects/items/weapons/grenades/chem_grenade.dm

@@ -114,7 +114,7 @@
 
 	activate(mob/user as mob)
 		if(active) return
-	
+
 		if(detonator)
 			if(!isigniter(detonator.a_left))
 				detonator.a_left.activate()
@@ -216,9 +216,11 @@
 		var/obj/item/weapon/reagent_containers/glass/beaker/B1 = new(src)
 		var/obj/item/weapon/reagent_containers/glass/beaker/B2 = new(src)
 
-		B1.reagents.add_reagent("aluminum", 25)
-		B2.reagents.add_reagent("plasma", 25)
-		B2.reagents.add_reagent("sacid", 25)
+		B1.reagents.add_reagent("aluminum", 15)
+		B1.reagents.add_reagent("fuel",20)
+		B2.reagents.add_reagent("plasma", 15)
+		B2.reagents.add_reagent("sacid", 15)
+		B1.reagents.add_reagent("fuel",20)
 
 		detonator = new/obj/item/device/assembly_holder/timer_igniter(src)
 

code/modules/reagents/Chemistry-Reagents.dm

@@ -1121,26 +1121,15 @@ datum
 			reagent_state = LIQUID
 			color = "#660000" // rgb: 102, 0, 0
 
-//Commenting this out as it's horribly broken. It's a neat effect though, so it might be worth making a new reagent (that is less common) with similar effects.	-Pete
-/*
+
 			reaction_obj(var/obj/O, var/volume)
-				src = null
 				var/turf/the_turf = get_turf(O)
 				if(!the_turf)
 					return //No sense trying to start a fire if you don't have a turf to set on fire. --NEO
-				var/datum/gas_mixture/napalm = new
-				var/datum/gas/volatile_fuel/fuel = new
-				fuel.moles = 15
-				napalm.trace_gases += fuel
-				the_turf.assume_air(napalm)
+				new /obj/effect/decal/cleanable/liquid_fuel(the_turf, volume)
 			reaction_turf(var/turf/T, var/volume)
-				src = null
-				var/datum/gas_mixture/napalm = new
-				var/datum/gas/volatile_fuel/fuel = new
-				fuel.moles = 15
-				napalm.trace_gases += fuel
-				T.assume_air(napalm)
-				return*/
+				new /obj/effect/decal/cleanable/liquid_fuel(T, volume)
+				return
 			on_mob_life(var/mob/living/M as mob)
 				if(!M) M = holder.my_atom
 				M.adjustToxLoss(1)

code/setup.dm

@@ -122,6 +122,7 @@
 
 //Plasma fire properties
 #define PLASMA_MINIMUM_BURN_TEMPERATURE		100+T0C
+#define PLASMA_FLASHPOINT 					246+T0C
 #define PLASMA_UPPER_TEMPERATURE			1370+T0C
 #define PLASMA_MINIMUM_OXYGEN_NEEDED		2
 #define PLASMA_MINIMUM_OXYGEN_PLASMA_RATIO	20