Carbon Dioxide, (CO2)

CO2 is a gas that occurs naturally in Earth's atmosphere. It is a product of the burning or corrosion of any carbonic compound. It is 60% heavier than dry air, making it an asphyxiant in confined spaces. It has a distinct odour that is only apparent at hazardous concentrations of over 3.9% by volume. CO2 is absorbed by plants to form carbohydrates through photosynthesis, releasing oxygen into the atmosphere. It is one of the greenhouse gases. CO2, although not toxic per se, is still considered a hazardous substance because of its propensity to replace ambient air, lowering oxygen levels. Lower oxygen levels are associated with concentration problems, headaches and general feelings of discomfort, even at concentrations below 1% by volume. This makes it important to monitor CO2 levels in places where people gather in poorly ventilated rooms, such as class rooms. CO2 is measurable through colorimetric detection tubes and specialized infrared sensors. Special models for class room use exist to alert occupants of the need to ventilate the room.