IAQ UK is an independent organisation with the aim of 'raising the agenda of indoor air quality within the home and workplace'

IAQUK Resources - Carbon Dioxide


There can be many sources of carbon within the workplace, but the greatest source of carbon dioxide is humans. The air breathed out of the lungs contains approximately 15% oxygen and 5.6% CO2. A person at rest inhales and exhales approximately 6 litres of air per minute, but in times of stress, this may increase to more than 100 litres per minute.


Carbon Dioxide is essential to human physiology and is important to maintain a ellibum of Carbon Dioxide and other criteria gases.  Carbon Dioxide is often considered a waste gas, but Carbon Dioxide is critical to our respiratory system and cellular metabolism.  Carbon Dioxide is the stimulant for breathing, not enough CO2 in our bodies creating an increase of breathing rate.

Carbon Dioxide with the molecular formula CO2.

Carbon Dioxide has often been used as an indicator as to the acceptability of indoor air quality, the suitability of air flow exchange and whether there is sufficient fresh air within enclosed spaces.  However Carbon Dioxide is an important factor within indoor air quality, with strong evidence to suggest a correlation between carbon dioxide build-up and an individual’s comfort, health and performance, just as significant as humidity and temperature.


Carbon Dioxide has a significant place in history; in the 17th century carbon dioxide was one of the first gases to be recognised as different from air, being denser and not supporting either flame or animal life.  Chemist Jan Baptist van Helmont, the first chemist to determine the different components in the air, coined the phrase ‘spiritus sylvestre’ (wild spirit), now known as Carbon Dioxide.  


Carbon Dioxide is an odourless, colourless atmospheric gas comprising of one carbon and two oxygen atoms.  It is one of the most abundant gasses in the atmosphere and plays a vital role in plant photosynthesis and animal/human respiration.  Carbon Dioxide derives primarily from combustion of organic matters, particularly the burning of fossil fuels.  Furthermore it is used for various processes, from carbonating drinks, to fire extinguishers, artificial fermentation in various food products, refrigeration equipment and compressed products.


Health Effects

It is difficult to provide a direct cause of health effects associated with indoor air quality, but collective research has indicated that Carbon Dioxide exceeding 800ppm will result in a range of health and comfort factors, including headache, fatigue, eye symptoms, nasal symptoms and respiratory tract symptoms.


Productivity has also been shown to reduce by 30% with regards to an individual’s cognitive processes. Carbon Dioxide can affect individuals with sensitivities to changes in air quality and can contribute towards some conditions such as migraines. Even mental health conditions such as stress, anxiety and depression have significant contributing factors.


Raising Carbon Dioxide concentrates within the environment increases blood flow which consequently raises body temperature.  This rise could cause the individual difficulties in accurately predicting the environment temperature and often feel the temperature is warmer than actual.

Technical - Carbon Dioxide - CO 2

  • 2 oxygen atoms bonded with a single carbon atom
  • Colourless gas
  • Odourless
  • CAS Number: 124-38-9
  • LTEL - 5000ppm (9150 mg/m³)
  • STEL - 15000 (27400 mg/m³)
  • IAQ recommended levels 380ppm - 800ppm



Carbon Dioxide is measured in parts per million.  PPM is often used to define a concentration of a substance.  1 ppm is 1 part per 1,000,000.


Carbon Dioxide is intrinsically linked with environmental factors and the increasing concern about climate change.  Typical outdoorconcentrations are between 350ppm – 450ppm.  However Carbon Dioxide has progressively risen in the atmosphere from 280ppm in 1850 to 381ppm in 2005, the 130ppm rise has been contributed by the industrial revolution in the 19th century. Scientists analysing the ancient Antarctic ice have reported no Carbon Dioxide concentrations around 380ppm in the past 650,000 years.    The Intergovernmental Panel on Climate Change (IPCC) projects that atmosphere Carbon Dioxide levels should reach 450-550ppm by 2050, possibly resulting in higher temperatures and rising sea levels.


Typical indoor concentrations can range from 380ppm – 2500ppm, although in poorly ventilated spaces, these levels can be greatly exceded. The Workplace Exposure Limits EH40/2005 supplement the Control of Substances Hazardous to Health Regulations 2002  enforcing 5000 ppm long term exposure (8 hour TWA) to protect against undesirable changes in the acid–base balance of the body. Although CO2 workplace exposure limits are not exceeded, lower concentrates of 1,000ppm have be shown to affect the body physically and psychologically.


CO2 can be monitored in the atmosphere, but also for clinical methods to measure the CO2 within someone.


Colorimetric gas detection pump and tubes


Colourimetric detectors work on a similar principle, a measured volume of air is drawn through a tube which contains chemicals which change in colour in response to the presence of a specific target gas, in this case carbon dioxide.  The chemicals within the tube will change colour according to the amount of carbon dioxide within the sample and is translated into a linear scale to provide an accurate reading of the percentage of carbon dioxide in ppm within the sample. Colourimeteric gas detection tubes are produced by different manufacturers are not necessarily interchangeable among gas detection pumps. Therefore it is important to ensure you have read the manufacturers instructions and recommendatios.


Electronic meter


There are several electronic diagnostic carbon dioxide instruments on the market, with integrated sensors for measuring and monitoring carbon dioxide, evulating average, maximum and minimum statistics.  Such meter can be user friendly for spot measurement orcontinious monitoring.  It is important to ensure the meter has a good concentration range, typically for indoor environment a minimum of 0 – 5,000ppm.  Ensure the analyser is calibrated before sampling and that each recording is made over a minimum of 60 seconds.


To evaluate effectiveness of ventilation and identify sources of carbon dioxide, an external reading should be taken, if possible next to the mechanical intake to evaluate external concentration influences.




A capnograph also takes a measurement of carbon dioxide within an air sample, but is more commonly used within clinical settings to measure CO2 content on human inspired orexpired air from respiratory gases. Capnographs work on the principal of using an infra-red light that beams to a sensor, as gas passes through the beam, high levels of CO2 reduce light directed at the beam, thus indicating concentrations.


Typically such monitoring would be carried out by a competent clinician, however understanding the importance of CO2 on the human physiology will enable practitioners to explore the relationship between the environment and health effects.


The Health and Safety Executive recommend a minimum fresh-air flow of 8 litres per second per person to maintain a satisfactory level of oxygen and Carbon Dioxide.  There are many positive advantages to mechanical ventilation, such as the ability to exercise more precise control over the environment and the make-up of air supply, as opposed to opening a window which is determined by the turbulence of natural wind.  This makes it difficult to assess the requirements of a ventilation system when it is used in conjunction with natural ventilation.    An adequate fresh air supply is required within the working environment to ensure that  occupants receive a satisfactory level of oxygen and carbon dioxide.  In addition, a much higher supply rate of fresh air is required to remove contaminants, pollutions and pollens within the indoor environment.   A higher percentage of recirculated air increases the risk of indoor pollutants.  However, mechanical ventilation and air conditioning systems have components that are susceptible to failure and to poor designer installation.   Failure to maintain and service could result in a reduction in quantity of fresh air drawn in from outside, thereby increasing the proportion of air that is recirculated, thus harboring organic growth and distributing contaminants throughout a building. 


The environment should be assessed against complete mechanical failure, managing alternative means to supplement fresh air, evaluating the necessity for separate mechanical installation systems.  Whilst mechanical ventilation and air conditioning can exercise more precise overall environmental control, they allow little personal choice or local control.  Being unable to open a window could have a psychological impact on occupants due to the lack of perceived control over their environment.  The provision of outdoor air at a rate in compliance with national standards does not guarantee an acceptable quality of inhaled air.   Surveying indoor air quality can be quite challenging, firstly given the fact that indoor air is invisible and secondly as there are many disciplines within, including building structure, work activities, occupancy and technology and most challenging personal comfort.



  • Identify the number of occupants and activities within rooms, identifying periodic variations to the number of inhabitants and tasks.  Is there a correlation between an increased number of occupants and Carbon Dioxide levels?
  • Change in space use, contaminants, or operation may require a reevaluation of the required air supply and consequent implementation of changes.
  • Inspect maintenance and service records of mechanical ventilation systems to ensure compliance with regulatory standards for suitable air supply.  The reuse of return air from, store rooms, photocopying rooms etc should be prohibited.
  • Implement an indoor air quality audit. Select a monitoring point that is representative of general air quality, away from walls, partitions and corners, air supply diffusers, floor fans, heaters or direct solar light and away from local sources of pollutants such as printers and photocopiers.
  • Measure at set times of the day and week and introduce seasonal monitoring, as the air quality may change according to outside temperatures.
  • The level of fresh air intake also affects the level of pollution from internal sources, as often elevated levels of contaminates become apparent in winter when the fresh air supply is cut down in order to make space heating more effective.
  • Current technology now allows easy and relatively inexpensive measurement of Carbon Dioxide. Always ensure your instrument has been calibrated prior to and after use.
  • Ensure other indoor air quality factors such as humidity and temperature are recorded to validate the relationship between air supply and air quality. An increase in Carbon Dioxide can demonstrate a reduction in humidity and increase in temperature. Thus the synergistic effect of Carbon Dioxide is interrelated.
  • Monitor sickness and absence data comparing with indoor air data to identify any trends.
  • Although subjective, an individual’s opinion via a quantifiable questionnaire on quality of indoor air and/or health symptom questionnaire can also assist with proactive monitoring.