Indoor Air Quality (IAQ) refers to the air quality in a space within a building, with particular reference to its potential impact on the health of occupants. There are many factors that can affect IAQ, including volatile compounds from furniture and fittings, microbial contaminants and carbon dioxide (CO₂). 

As carbon dioxide is a by-product of respiration and is exhaled as a waste product, it is a good indicator of occupancy and the level of physical activity within a ventilated space. For that reason, the CO2 level as measured by sensor is often used as the primary measure for Demand Controlled Ventilation, producing a corresponding increase in ventilation rate with rising CO2 levels. 

Raised levels of carbon dioxide have an adverse effect on alertness, whereas very high concentrations can give rise to health problems. 

Effects of CO2 levels :

• 400-1000 ppm – Normal conditions 
• 1200-2000ppm – Fatigue, lack of concentration 
• 2000-5000ppm – Fatigue, headaches, general discomfort 
• >5000ppm – Increased heart rate, nausea, oxygen deprivation