Fog Question

You can have multiple env_fog_controllers in a map and change which one the player is using with a trigger_multiple that sends the input SetFogController to !activator with the parameter being the name of the e_f_c you want. Keep in mind though this doesn't make a specific area foggier (looking at the area does nothing, only walking through the trigger makes it change), other methods of make an area smoke filled are generally more resource intensive but you can try playing with them too: func_dustcloud and func_smokevolume.