fire smoke inhalation is dangerous in any quantity. Too much smoke inhalation puts too much carbon monoxide into your lungs. Carbon Monoxide prohibits hemoglobin from transferring oxygen into your body and carbon dioxide out of your body. Any time of repeated exposure will cause brain damage. Its usually prevalent that you would pass out before dying of smoke inhalation. If i were to put a number on it, i would say 15 minutes of straight smoke (0% oxygen) would kill you, 5-10 minutes would cause permanent brain damage. If there is more oxygen in the room, then you would have more time (but not much). Fire burns oxygen, so as a fire continues to be active, more oxygen gets removed from the room.