The NDIR sensor is all solid state so there are no parts to degrade or wear out. The sensor depends on the absorption of light by the CO2 molecules. A light inside the sensor is turned on and off. For a detailed explanation refer to Application Note ITI-037 which discusses this technique in detail. The early symptoms are headache, dizziness and restlessness.
Higher concentrations can cause increased heart rate, pulse pressure and blood pressure.
Occasionally convulsions can occur. Eventually the exposure can lead to coma and asphyxiation. The frequency of measurement depends on the dynamics of the situation. A measurement should be made periodically and whenever the occupants of an area complain of the symptoms associated with over exposure. Measurements should also be made in accordance with OSHA's confined space regulation.