You are correct about the low O2 concentration. One thing to consider with any type of filtration system in heavy smoke/toxic fumes, is the possible lack of O2. While the filtration system can and will filter the smoke and toxic fumes, oxygen may be displaced enough so that the filtered air that is actually being breathed may not have an oxygen concentration sufficient to support life. That is why when we are involved in a structural fire, we wear self-contained-breathing-apparatus (SCBA) or for confined space rescues supplied-air-breathing-apparatus (SABA), which supply's us with breathable air. Due to both heat and low oxygen, the adage of keeping low to the floor in the event of fire/smoke filled room/building, would still apply even if one is wearing a filtration device. The filtration device should not lead to a false sense of security; your main goal should still be to get out as soon as possible. Pete