Protections from CO/CO2 Poisoning in Rooms?
If there is no oil/gas/wood burning/ heating system in the near, the natural air change through house hulls is enough to prevent a dangerous concentration. If the house is built with a very air tight hull (e.g. passive houses) , a ventilation system provides the air exchange. Air exchange via fully opened window every few hours helps also to avoid high CO2/CO levels. In general, not high Carbon(di)oxide levels , but fine dust from candles/smoke or aerosols from cleaning agents/moebels etc. or asbestos from building materials used in the past (radiator wall coatings, cement flooring, pipe insulation, PVC floor or tile glue, Eternit Wall covers etc. if sawed/grinded/broken/drilled) are the biggest threat for the health.