How harmful is fireplace smoke

hello guys... In my basement suite I have a wood fireplace and so does my landlord upstairs... when I have fires smoke is never an issue... but my landlord warned me that sometimes it backdrafts.. there are 2 seperate chimmeneys but it just comes down at the top... anyways it hasnt happend ever so i never thought about it.,.. but today i could smell it more then usual..
not like heavy smoke at all you couldnt even see it just a strong smell
my worry is will this kill my birds>? i know it is not good for them but im sure it wont happen often if at all..
but if one day im not home to open all the windows etc will they die?
thanks.. and they need to be in this room! unless they will be alone in my bedroom all the time and i dont want that

 

I don't think this is going to be a problem as i used to breed pigeons and one fell down the chimney when it was it was ot flying with the others and it was down there a good few hours and when we got him out he was fine apart from being covered in soot from the chimney.

So i guess it all depends on the severity of the smoke it can not be that toxic to birds if it does not affect birds living outside.

Mike