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We don’t often think about the quality of our indoor air. Usually it’s a  mix of various gases, dust, and water vapour. But the one thing that can easily turn a comfortable room unbearable is carbon dioxide (CO2). There are legal limits to the level of carbon dioxide that you can expose people to. A high level of carbon dioxide in a room indicates inadequate ventilation. This can cause headaches, fatigue, eye and throat irritation, increased heart rate, dizziness, rapid breathing, and visual and hearing dysfunctions.

Man yawning

Carbon dioxide (CO2) is actually an indicator of a wider range of indoor pollutants emitted by humans, and correlates with human metabolic activity. Carbon dioxide at levels that are unusually high indoors may cause occupants to grow drowsy, get headaches, or function at lower activity levels. As humans are the main indoor source of carbon dioxide, it’s easy for the levels to increase in a building full of people. Hence indoor CO2 levels are an indicator of the adequacy of outdoor air ventilation relative to indoor occupant density and metabolic activity.

As a general rule of thumb, 1000ppm should be used as an upper limit for all indoor areas. Exposure to higher levels may cause unconsciousness or death within minutes of the exposure.

  • Normal outdoor air typically has about 360 ppm (parts per million) CO2.
  • At 600 ppm people notice the air feels “stuffy”.
  • 1000 ppm is recommended as the upper limit of CO2 for indoor areas, but at this level it really indicates inadequate ventilation. People will complain of fatigue, headaches and eye/throat irritation.
  • At 10,000ppm (1% CO2 concentration) some people will begin to feel shortness of breath, breathing difficulties, rapid pulse rate, headaches, hearing loss, hyperventilation, sweating, and general fatigue. Prolonged exposure can cause drowsiness.

To eliminate most Indoor Air Quality complaints, total indoor carbon dioxide should be reduced to levels recommended by various international bodies:

  • NIOSH considers that indoor air concentrations of carbon dioxide that exceed 1,000 ppm are a marker suggesting inadequate ventilation.
  • ASHRAE recommends that carbon dioxide levels not exceed 700 ppm above outdoor ambient levels.
  • The UK standards for schools say that carbon dioxide in all teaching and learning spaces, when measured at seated head height and averaged over the whole day should not exceed 1,500 ppm. The whole day refers to normal school hours (i.e. 9.00am to 3.30pm) and includes unoccupied periods such as lunch breaks.
  • European standards limit carbon dioxide to 3500 ppm.
  • OSHA limits carbon dioxide concentration in the workplace to 5,000 ppm for prolonged periods, and 35,000 ppm for 15 minutes.

CO2 graphic
So how do you control the CO2 level? The first thing to do is measure it.

Esis offers a range of CO2 instruments and sensors. For simple ease of use indoors, we recommend the KeepAlert range of CO2 instruments, a cost effective range of Carbon Dioxide monitoring and alerting instruments. There are very few CO2 instruments on the market that are as cost effective and convenient as the KeepAlert range.

KeepAlert instruments are designed to measure CO2 levels as well as temperature and humidity. Two kinds of instrument are available:

  • Meters
  • Data Loggers

The KeepAlert Desktop/Wallmount meter simply plugs into a power point and monitors the CO2 level, Temperature and Humidity. The KeepAlert Handheld CO2 Meter measures up to 10% CO2 levels. Ideal for spot checking many locations.

KeepAlert CO2 meter
The Testo 160 IAQ WiFi Data Logger with display is designed to measure CO2 levels as well as temperature and humidity. This WiFi enabled instrument automatically uploads the measurements to the cloud, for easy access via smartphone or web browser.

For permanent installations in buildings, a CO2 sensor can be connected to a BMS (Building Management System), or the sensor can have its own relay to control ventilation fans. For this kind of application we recommend Vaisala’s range of CO2 sensors and transmitters.

You can start monitoring your indoor air quality very easily using the KeepAlert Desktop meter, or to keep tabs on it over a period of time we also have indoor air quality data loggers. For more information please contact us.

(parts courtesy Wikipedia)

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